Assessing SARS-CoV-2 Vaccine Effectiveness in Health Workers: A Cohort Study in Five Al-Azhar University Hospitals, Egypt

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El Shazly, and 42 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5754076/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 26 Sep, 2025 Read the published version in BMC Infectious Diseases → Version 1 posted 10 You are reading this latest preprint version Abstract Objective: A cohort study was conducted with the support of the WHO, where a standardized WHO protocol was followed to measure vaccine effectiveness (VE) against symptomatic RT‒PCR confirmed SARS‒CoV-2 infection among hospital health workers (HWs) eligible for vaccination at Al-Azhar University hospitals. Methods: A WHO-supported cohort study was conducted from July 2022 through September 2023 and included 1249 HWs who were randomly selected and followed up biweekly for one year. At enrollment, nasopharyngeal (NP) and blood samples were collected from each participant and evaluated to detect SARS-CoV-2 RNA via a real-time PCR assay (QIAGEN) and for the quantitative detection of SARS-CoV-2-binding antibodies via the Roche Elecsys Anti-SARS-CoV-2 S immunoassay (Roche Diagnostics, GmbH, Germany). During follow-up, NP samples were collected from anyone who developed symptoms consistent with the WHO definition of suspected cases of SARS-CoV-2 infection. Results: At enrollment, SARS-CoV-2 RNA was detected in 119/1235 (9.6%) HWs and 89% of the participants with positive RNA were asymptomatic. COVID-19-binding antibodies were detected among 1245/1248 HWs (99.8%), and 53.2% had titers > 2500, regardless of vaccination status. During follow-up, 232 participants had COVID-19 symptoms, but only 109 provided NP samples, and 18 of them were positive for SARS-CoV-2 RNA. No hospitalization or mortality was recorded at enrollment or during the follow-up period. The cumulative incidence of COVID-19 infection was higher among HWs with incomplete vaccination compared to unvaccinated, fully vaccinated, or those who received booster doses (P =0.025). There was no significant difference in VE among HWs who were fully vaccinated or had booster doses compared with unvaccinated HWs, with adjusted VE values of 68% (95% CI -28% to 92%) and 64% (95% CI -170% to 95%), respectively (P = 0.106 and 0.318 respectively). The adjusted VE increased to 89% (95% CI -33% to 99%) among HWs with hybrid immunity compared with those who were unvaccinated with a previous COVID-19 infection (P =0.082). Conclusion: This study indicates that VE was higher among HWs with hybrid immunity compared to unvaccinated HWs with previous COVID-19 infection. The findingsalso highlight the importance of completing the primary vaccination series against COVID-19. This study reveals a high rate of asymptomatic COVID-19, a lower rate of confirmed cases, and a marked decrease in hospitalization and fatality rates at enrollment and during follow-up. Real-world VE studies are in need to address many unanswered questions, including the appropriate number of booster doses, duration of protection, and incidence of vaccine adverse events. COVID-19 vaccine effectiveness binding antibodies RT‒PCR health workers cohort study Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 INTRODUCTION The worldwide emergence of severe acute respiratory syndrome (SARS) caused by SARS-CoV-2, which is commonly known as coronavirus disease 2019 (COVID-19), has presented a significant challenge and a global public health concern. The severity of COVID-19 spans from asymptomatic infection to critical illness, resulting in fatalities, as reported by the World Health Organization (WHO). In September 2023, there were 770,875,433 confirmed cases of SARS-CoV-2, including 6,959,316 deaths globally, 23,394,122 confirmed cases in the Eastern Mediterranean and 9,569,874 in Africa, with cumulative cases of 516,023 and 24,830 deaths in Egypt (1) . Egypt reported its first case on 14/3/2020; then experienced five waves of COVID-19 until the end of May 2022, the fifth wave starting in the first week of 2022 and lasting for 16 weeks (2,3). By the beginning of the fifth wave, Omicron was the dominant SARS-CoV-2 variant in Egypt (4). Since the WHO declaration of the global pandemic of COVID-19 in March 2020(5), several types of vaccines against COVID-19 have been rapidly developed worldwide and recent studies have confirmed safety and effectiveness of these vaccines(6,7). As of May 2023, a total of 13,505,262,477 vaccine doses were administered(8) . Vaccination against SARS-CoV-2 is a leading strategy to change the course of the COVID-19 pandemic, as different types of COVID-19 vaccines are available worldwide. Each vaccine exhibits a different potency and duration of efficacy, as determined by the antigen design, adjuvant molecules, vaccine delivery platforms, and immunization method(9). The CDC assesses vaccine effectiveness through multiple observational studies that utilize various methods and uses data gathered from surveillance platforms, electronic health records, and prospective studies. These studies have demonstrated that VE is influenced by several factors including host-related factors (age, chronic illness, and history of previous infection), viral factors like circulating variant(s), vaccine related factors such as vaccine type and time since vaccination, the total number of doses received, and the duration since the most recent dose (10). A systematic literature review and meta-analysis on the effectiveness of COVID-19 vaccination against post-COVID conditions (long COVID) among fully vaccinated individuals showed that completed COVID-19 vaccination prior to being infected resulted in a significant decrease in long COVID throughout the study period. Vaccine effectiveness demonstrated an increase when booster doses were administered (11) Egypt introduced different types of vaccines, including inactivated vaccines such as CoronaVac® (Sinovac) and Covilo® (Sinopharm), Beijing; adenovirus vector vaccines such as Vaxzevria® (Oxford/AstraZeneca), Sputnik V® (Gamaleya Institute) and Jcovden® (Janssen); and mRNA vaccines such as Comirnaty® (Pfizer/BioNTech) and Spikevax® (Moderna) (12). Additionally, the Egyptian Holding Company for Biological Products and Vaccines (VACSERA) started producing doses of China's Sinovac SARS-CoV-2 vaccine. Stability studies on this vaccine were conducted, and it was administered to Egyptian citizens starting in August 2021 (13). Egypt started its COVID-19 vaccination rollout campaign on 24 January 2021 for medical personnel and began targeting individuals with chronic diseases and elderly individuals in March 2021. By the end of December 2023, 56% of the Egyptian population had been vaccinated with at least one dose, 41% had completed the primary vaccination series, and 15% had received at least one booster dose (14). A large-scale national survey of 18000 subjects was conducted by the Ministry of Health and Population from March–May 2022 in Egypt to determine COVID-19 vaccine coverage, which was low (48%) compared with the WHO 70% target (15).Thus, it is crucial to continuously evaluate and obtain updated effectiveness estimates of available vaccines against the prevalent strains of SARS-CoV-2. Real-world vaccine effectiveness (VE) studies can answer questions about effectiveness against transmission or disease outcomes by age group and risk factors, the duration of vaccine protection relative effectiveness of different vaccines, the relative effectiveness of one dose vs. two doses or more, as well as the effectiveness of the vaccine against new viral strains. Healthcare workers (HCWs) are at increased risk of SARS-CoV-2 exposure due to frequent contact with infected patients (16). A WHO sponsored multi-country case-control study conducted between August 2019 and November 2021 across 62 health facilities in 16 countries (1213 cases and 1844 controls) found prolonged patient contact (15 mins) significantly increased the likelihood of SARS-CoV-2 infection (OR 1.4; 95% CI 1.0–1.8)(17). Notably, following the COVID-19 pandemic, there were fewer VE studies from the Eastern Mediterranean Region (EMR) due to limited research infrastructure, expertise, and financial constraints. In response, from 2021 to 2023, the Eastern Mediterranean Regional Office of the World Health Organization (WHO-EMRO) provided technical, organizational, and financial support to enhance local research capacities and inform vaccine policies for the region. Four EMR countries – Egypt, Jordan, Iran, and Pakistan – were selected to participate, utilizing two WHO protocols: a cohort study among healthcare workers and a test-negative design at severe acute respiratory infection surveillance sites(18). WHO-EMRO conducted both general and country-specific workshops to build capacity in participating countries, developed tailored questionnaires uploaded to a centralized data platform (REDCap) to streamline data collection, and offered ongoing technical assistance for data quality checks and analysis to investigators. This approach enabled countries to independently analyze national VE data while facilitating pooling of data across countries and reporting regional VE estimates to inform vaccine policies. Thus, the aim of this study was to measure SARS-CoV-2 vaccine effectiveness (VE ) among HWs eligible for vaccination at Al-Azhar University hospitals against symptomatic RT‒PCR confirmed SARS-CoV-2 infection. SUBJECTS AND METHODS III-1-1 Study Setting A hospital-based prospective cohort study was carried out with support from the WHO at five university hospitals affiliated with Al-Azhar University, Egypt, focusing on HWs. Three of these hospitals are located in the Cairo governorate (representing the capital), one in the Damietta governorate (representing Lower Egypt), and one in Assuit governorate (representing Upper Egypt). The WHO’s protocol, design, and methodology for assessing COVID-19 vaccine effectiveness were customized to suit the specific context and settings of the country. II-1-2 Study Participants HWs affiliated with Al-Azhar University Hospitals were randomly selected, regardless of their COVID-19 vaccination status. All categories of health workers at these hospitals were eligible for inclusion in the study, provided informed consent was obtained. The study participants included all health workers who interact with patients, handle their body specimens, or manage potentially infectious waste. This included physicians, nurses, emergency medical personnel, laboratory technicians, and administrative staff. To participate, health workers had to be eligible for vaccination and have no contraindications to receiving the COVID-19 vaccine. The number of participants from each facility was estimated according to its total workforce size at each hospital: 300 participants from each hospital in Cairo, 200 from the hospital in Damietta, and 150 from the hospital in Assuit, with the total work force being 13260 HWs in the five hospitals. II-1-3 Sampling Criteria Stratified Random Sampling: Healthcare workers at each university hospital who consented to participate in the study, regardless of their COVID-19 vaccination status, were categorized into strata based on factors such as age group, gender, and job type. Inclusion criteria comprised all HWs affiliated with Al-Azhar University Hospitals irrespective of their vaccination status or prior infection. HWs who had already been vaccinated against COVID-19 as part of the routine COVID-19 vaccine rollout could be included, if detailed information about their vaccination was available. Exclusion criteria included HWs who were not eligible for COVID-19 vaccination (sever allergy, pregnancy, etc.), or those who refused to sign the informed consent. II-1-4 Participant enrollment and follow-up procedures The study objectives were communicated to HWs at the participating hospitals. The research team informed them about the importance of the study and the benefits of participation, including receiving their lab results. Participation was voluntary, with informed consent required, and participants could withdraw at any time without penalties, though they were asked to notify the team if they chose to do so. Enrollment took place from July to August 2022, and HWs who were ineligible for vaccination (due to factors like severe allergies or pregnancy) or who did not provide informed consent were excluded. Participants completed a face-to-face interview to complete a questionnaire after signing informed consent. All participants were interviewed and filled out an enrollment questionnaire that includes demographic, clinical, and epidemiological information, vaccination history, as well as occupation- and community-related behaviors. Regular ZOOM meetings were held to ensure proper study implementation at each hospital and monitor adherence to the study protocol by the team . Participants’ self-reported vaccination status was verified through sources such as occupational health records, vaccination cards, or vaccine registries. The Ministry of Health and Population (MOH&P) provided each vaccine recipient with a card detailing their vaccine information, and vaccines were distributed to the university hospitals through a cold chain system. Participants were registered online [ http://www.egcovac.mohp.gov.eg ], and each participant who consented to take the vaccine had to fill out an application form. Participation was voluntary, the vaccine was free of charge, and vaccination was postponed for 3 months for those who had a recent COVID-19 infection. Participation was encouraged through a national advertising campaign. Samples were transported to the Virology Laboratory, Microbiology Department, faculty of Medicine-Al-Azhar University and stored at -80°C for evaluation of the presence of SARS-CoV-2 RNA via real-time RT‒PCR, whereas the serum samples were transported to clinical pathology laboratories and stored at -20°C at Al-Zahraa, Al-Hussein and Bab-AlSharia hospitals for SARS-CoV-2-binding antibody quantitation. Follow-up phase: participants in each hospital were grouped (20-25) for each investigator, who had a list of his or her assigned participants’ phone numbers. Participants were monitored biweekly by investigators, who contacted them via phone calls or WhatsApp to complete follow-up questionnaires. Regular reminders were sent before follow-up appointments. In case of COVID 19 symptoms, the investigator examined the participant in the hospital and took a nasopharyngeal swab if indicated. The objective of the follow-up was to: Identify among the cohort of participant HWs new cases, Track changes in vaccination status, Monitor changes in potential exposures. If participants exhibited COVID-19 symptoms, a nasopharyngeal swab was taken, and those who failed to respond within 48 hours were contacted again via an alternative method of communication (phone call or WhatsApp message) or visiting them at their workplaces, if they declined to continue, their reasons were documented. Nasopharyngeal swabs were taken within 24–48 hours from participants suspected of infection who had a history of contact with COVID 19 patients and met the following WHO COVID 19 case definition; acute onset of fever and cough OR acute onset of any three or more of the following symptoms in the previous 7 days: fever, cough, general weakness/fatigue, headache, myalgia, sore throat, coryza, dyspnea, anorexia/nausea/vomiting, diarrhea, altered mental status, anosmia, or ageusia (19). The investigator in each group was responsible for taking the nasopharyngeal swab. Samples were sent directly or stored at -20°C for a few days and then transferred to the virology lab in Cairo for analysis. Those who refused testing were considered dropouts, and their data were recorded as missing. All follow-up interactions were documented using standardized written records to ensure consistency in data collection. The follow-up questionnaire was completed, and the data was collected in Excel sheet, with a copy delivered to the project manager. At the end of the study, 1230 HWs completed the biweekly follow-up, with 14 excluded due to dropout after enrollment (death, retirement, or a change of workplace). “Breakthrough infections” is a term used to describe infections in fully vaccinated people, while “non-breakthrough infections” refers to infections in unvaccinated people, who, apart from their vaccination status, are similar to the vaccinated (20). III-1-5 Data Collection Procedures The WHO provided financial and technical support for methodology, data management, report development and statistical analysis of the data (21,22) The data collection forms were based on the WHO protocol and relevant questionnaires (23). Five questionnaire forms were included, each customized to fit the study requirements. The enrollment questionnaire captured data on demographics; clinical and epidemiological information; comorbidities; working conditions; social activities; community-related behaviors; COVID-19 prevention; and previous history of SARS-CoV-2 infection and COVID-19 vaccination. The laboratory questionnaires (serology/virology) included dates, types of specimens, tests and results, while pre-enrollment and follow-up questionnaires were also included. III-2 Sample size calculation: The sample size was calculated based on Table 2 in the WHO protocol (24) Assuming a vaccine effectiveness of 60% and that 20% of unvaccinated HWs would be infected with SARS-CoV-2 over a period of 12 months and vaccination coverage among HWs of 90%, the required minimum sample size of 1006 participants was calculated. Accounting for an expected 20% loss to follow-up during the one-year follow-up period, 1250 participants ultimately needed to be included. III-3 Ethical considerations: Each participant was allocated a unique study ID number with a barcode at enrollment which was scanned at all subsequent steps to identify each respective individual’s documents and test. Name and national ID number were included in study databases. Personal identifying information was maintained only by the person responsible (s) in each study site in accordance with regulatory agencies requirements. To ensure confidentiality, anonymization techniques were implemented by removing sensitive data including personally identifiable information, implementing safeguards against participant identification during data entry. III-4 Laboratory Investigations: III-4-1 Detection of SARS-CoV-2 binding: Total antibodies against the receptor binding domain (RBD) of the S protein were detected in serum samples collected at enrollment via the Roche Elecsys Anti-SARS-CoV-2 S immunoassay on a Roche Cobas e 411 (Roche Diagnostics, GmbH, Germany). The limits of the blank (LoB) and limit of detection (LoD) were 0.30 U/mL and 0.40 U/mL, respectively. Test results <0.8 U/mL were classified as nonreactive, whereas those ≥0.8 U/mL were classified as reactive. The upper limit of the kit was 250 U/ml, and due to a high number of positive samples that were out of range, all samples were diluted 1:10 to obtain values ≤2500. III-4-2 Real-time RT‒PCR: Reverse-transcriptase polymerase chain reaction (RT‒PCR) for SARS-CoV-2 was performed using real-time RT‒PCR for samples collected at enrollment and for all symptomatic participants who met the WHO suspected case definition. The detection of SARS-CoV-2 RNA was performed via real-time PCR via a qualitative real-time RT‒PCR kit (the artus® SARS-CoV-2 Prep and Amp UM Kit -QIAGEN-Germany) targeting 2 viral genes (N1 and N2 of the N gene were detected through the same fluorescence channel). The two targets were not differentiated, and amplification of either or both targets led to the generation of fluorescence signal genes. The sample preparation and detection steps were integrated into a single kit with a limit of detection of 950 cp/ml. A sampling control (RNase P) and internal RNA control, together with positive and negative external controls, were included. Invalid results were obtained for a noticeable number of samples. Thus, RNA extraction (QIAamp DSP Virus spin kit) was performed for invalid samples, where a larger sample volume was tested (200 µl instead of 10 µl), adequate extraction and purification of viral RNA by enzymatic lysis and mixing (protease +buffer AL with carrier RNA), and then RT‒PCR steps with the artus® SARS-CoV-2 Prep and Amp UM Kit were conducted (bypassing its extraction step). The results were conclusive. III-5 Statistical Analysis: Data entry into the REDCAP program occurred under the guidance and support of the WHO-EMRO technical team. Participant’s name, address, phone, and mobile number were excluded, as this information was kept only with the follow-up team. Statistical analysis was carried out using SPSS for Windows, version 23. Categorical variables were presented as numbers and percentages, and continuous variables as medians and IQRs. Different statistical methods were used to assess the significance level for the differences between the study groups according to their vaccination status. Chi-square was used to detect the significant difference between categorical variables, and Fisher’s exact test was used if the expected number was below 5 in any cell. For continuous variables, one-way ANOVA was used for parametric data and the Kruskal-Wallis test for non-parametric data. Survival analysis was carried out using the Kaplan-Meier test, and a curve was generated to inspect the cumulative incidence according to vaccination status. The primary outcome, primary series vaccine effectiveness (VE) was estimated against COVID-19. COVID-19 case was defined as a positive PCR result in a symptomatic participant with symptom onset within 14 days prior to the follow up interview. Vaccine effectiveness percent (VE%) was estimated using Cox regression proportional hazards models; hazard ratios comparing vaccinated and unvaccinated were estimated with vaccination as a time-varying exposure. VE% = 1 – hazard ratio [HR]* 100, where the HR = Exp (B) in the Cox regression model. Follow-up time was from baseline to the time of symptomatic SARS-CoV-2 confirmed with positive PCR or study exit. The 95% CI of VE was computed based on the 95% CI of the HR in the Cox regression. Subgroup analyses by vaccination doses (partial, fully vaccinated, and booster dose vs unvaccinated; different vaccine type vs unvaccinated; then fully vaccinated vs unvaccinated and vaccine type regarding the prior infection) were performed. For VE calculation, prior infection depends on RT-PCR positivity, either before or at enrollment, or positive serology at enrollment for unvaccinated participants. However, for prior infection, 15 participants were excluded when calculating the VEs, as 14 of them had missing RT-PCR results at enrollment (7 sample results were inconclusive / invalid and 7 were dried samples) and one missing a serology sample. These missing PCR results were at random, from different hospitals. An additional analysis was planned to stratify VE% estimates by time since vaccination, e.g., 14-89 days, 90-179 days, and >=180 days. Follow-up was identified from the start of being at risk to the earliest of outcome or study exit. However, the median duration from receiving the 2nd dose till the end of follow-up was 631 days (IQR: 557-730 days), and between the booster dose and the end of follow-up was 394 days (IQR: 319-491 days). Thus, we only stratified the duration into 365 days. Confounding factors and effect modifiers Both unadjusted and adjusted estimates of VE were presented. Adjustment was made in the Cox regression model for potential confounders (age, sex, chronic comorbidities, and health facility). Hospitals were categorized in two: Cairo hospitals (Al-Zahraa, Al-Hussein, and Bab-Alsharia) and peripheral (Damiatta and Assuit). Adjustment was made in the multivariable cox regression model for all potential confounders. None of these variables were significant when multivariate Cox regression backwards Wald analysis was done. Sensitivity analysis Sensitivity analyses were performed to estimate the robustness of the VE estimates produced in the main analysis against different assumptions (e.g., assumptions made on missing data) and/or sources of bias (e.g., the effect of unmeasured confounding factors). Based on the assumptions made and on the different sources of bias identified, different sensitivity analyses were performed: ● Excluding participants with shorter than expected vaccination intervals between the 1st and 2nd dose and including those with <21 days between the first and second dose of vaccine. ● Consider being at risk after 60 days after previous infection detected by PCR versus 90 days. ● Exclusion of symptomatic patients who refused to give nasopharyngeal swabs versus including them in the VE% estimation. RESULTS Out of the 13260 HWs, 1249 were recruited into the study and agreed to be followed up biweekly for a period of one year. At enrollment, most of the included HWs, 911/1249 (72.9%), had completed the primary vaccination series (one dose of Johnson and Johnson vaccine or two doses of any other vaccine), 179 had received a booster dose (14.3%), 52 were partially vaccinated (4.2%) with one dose, and 107 (8.6%) were unvaccinated. At enrollment, COVID-19 RT‒PCR was performed for 1235 (98.8) participants, with 14 samples excluded (missed, dried or inconclusive results). There were 148 (11.95) symptomatic cases among the 1235 HWs at enrollment, 13 (8.8%) of whom had COVID-19-positive results. COVID-19-binding antibody titters were measured in 1248 HWs with one missing value. A total of 1230 HWs were followed up for 1 year, while 14 (1.1%) participants dropped out just after enrollment and 5 (0.4%) dropped out before contribution as person-time at risk (within 90 days from the date of PCR positive at enrollment). Out of 1230 participants, 232 (18.9%) experienced symptoms, but only 108 (46.4%) agreed to provide nasopharyngeal samples. Out of them, 18 had PCR positive (16.7%), figure (1). IV-1 Baseline characteristics: The cumulative COVID-19 vaccine coverage among the study participants is shown in Figure (2). Their vaccination started in January 2021 and continued until August 2022. Notably, all vaccinated participants completed their primary vaccination series (full doses) before enrollment, except one, who received his / her booster dose one month after enrollment and during the follow-up period. Demographic and clinical characteristics by vaccination status at enrollment are presented in Table (1). More than half of the recruited HWs were females (697, 55.8%), and the median age was 40.0 (30.0--49.0) years, with half of the partially vaccinated HWs between 17 and 30 years old and 43.9% of the unvaccinated HWs in the age group 31–40 years. Those who had completed a primary vaccination series or had a booster dose showed nearly equal age group distributions. Most of the participants were nurses, 536 (42.9%), with other HW categories, including physicians, technicians, admins and workers. Overall, most HWs were healthy, with 927 (74.2%) not reporting any chronic disease. Among those with chronic disease, hypertension and diabetes were the most common medical conditions (12.1% and 10.5%, respectively). Sinopharm followed by AstraZenca were the most used vaccines among the studied HWs ,481 (38.5%) and 391 (31.3%), respectively. The median and IQR between completion of the primary vaccination series and the start of follow-up was 298 days (235–388), whereas the median time between the booster dose and the start of follow-up was 157 days (IQR: 77–201). A total of 308 (25.0%) HWs had a history of previous infection, as shown by RT‒PCR positive before/ at enrollment and/or serology positive, representing 164 (18.2%) of those who had completed their primary vaccination series, and 106 (100%) of the unvaccinated participants, with significant differences between groups (P < 0.001). IV-2 Follow-Up (FU): The total follow-up period was 1148.6 person-years, and the average follow-up period was 0.94 years. Participant demographics and clinical characteristics of 1230 participants by vaccination status at the end of follow-up are presented in Table (2), where 19 participants dropped out after enrollment. Participants were followed up biweekly for one year, with 232 (18.9%) HWs developing symptoms and only 108 (46.4%) of them provided NP swabs, Fig (1). Five participants dropped out before contributing as person-time at risk (they were RT‒PCR positive at enrollment but dropped out within 90 days from enrollment. Partial loss to follow up was recorded for 179 participants. All those who were lost to follow up were assessed at their next visit regarding vaccination or symptoms during the missed period. The median duration from receiving the 2nd dose until the end of follow-up was 631 days (IQR: 557–730 days), while the booster dose to the end of follow-up was 394 days (IQR: 319–491 days). The cumulative incidence of COVID-19 breakthrough infections was higher among HWs partially vaccinated than among those who were unvaccinated or those who received two or three doses of vaccine ( p =0.025) (Figure 3). Table (1): Participant Demographics and Clinical Characteristics by Vaccination Status at Enrollment Variable © All Participants Unvaccinated Partially Vaccinated * Fully Vaccinated** Booster Dose P value Total No. (%) 1249 (100%) 107 (8.6%) 52 (4.2%) 911 (72.9%) 179 (14.3%) Age Group (years) 17-30 315 (25.2%) 26 (24.3%) 26 (50.0%) 226 (24.8%) 37 (20.7%) 50 261 (20.9%) 17 (15.9%) 3 (5.8%) 192 (21.1%) 49 (27.4%) Median (IQR) 40.0 (30.0-49.0) 36.0 (31.0-44.0) 30.50 (27.0-37.0) 41.0 (31.0-49.0) 43.0 (35.0-51.0) Sex Male 552 (44.2%) 44 (41.1%) 29 (55.8%) 396 (43.5%) 83 (46.4%) 0.287 Female 697 (55.8%) 63 (58.9%) 23 (44.2%) 515 (56.5%) 96 (53.6%) Job Physician 156 (12.5%) 18 (16.8%) 15 (28.8%) 101 (11.1%) 22 (12.3%) <0.001 Nurse 536 (42.9%) 60 (56.1%) 19 (36.5%) 370 (40.6%) 87 (48.6%) Technician 73 (5.8%) 4 (3.7%) 1 (1.9%) 61 (6.7%) 7 (3.9%) Administration 270 (21.6%) 11 (10.3%) 7 (13.5%) 224 (24.6%) 28 (15.6%) Workers 196 (15.7%) 12 (11.2%) 10 (19.2%) 143 (15.7%) 31 (17.3%) Others 18 (1.4%) 2 (1.9%) 0 (0.0%) 12 (1.3%) 4 (2.2%) Chronic Illness No 927 (74.2%) 83 (77.6%) 45 (86.5%) 670 (73.5%) 129 (72.1%) 0.145 Yes 322 (25.8%) 24 (22.4%) 7 (13.5%) 241 (26.5%) 50 (27.9%) Vaccine Brand Sinovac 85 (6.8%) 0 6 (11.5%) 66 (7.2%) 13 (7.3%) <0.001 Sinopharm 481 (38.5%) 0 12 (23.1%) 419 (46.0%) 50 (27.9%) AstraZeneca 391 (31.3%) 0 26 (50.0%) 325 (35.7%) 40 (22.3%) Moderna 22 (1.8%) 0 3 (5.8%) 7 (0.8%) 12 (6.7%) Johnson and Johnson (Janssen) 12 (1.0%) 0 0 (0.0%) 10 (1.1%) 2 (1.1%) Pfizer 140 (11.2%) 0 5 (9.6%) 74 (8.1%) 61 (34.1%) Heterologous 11(0.9%) 0 0 (0.0%) 10 (1.1%) 1 (0.6%) SARS-CoV-2 spike binding antibodies No 3 (0.2%) 0 (1 missing) 0 3 (0.3%) 0 0.151 Yes 1245 (99.8%) 107 (100.0%) 52 (100.0%) 908 (99.7%) 179 (100.0%) Evidence of previous infection Ω No 926 (75.0%) 0 (0.0%) (1 missing) 45 (88.2%) (1 missing) 735 (81.8%) (12 missing) 146 (82.0%) (1 missing) <0.001 Yes 308 (25.0%) 106 (100.0%) 6 (11.8%) 164 (18.2%) 32 (18.0%) © The percentages reported by column * Partially vaccinated : 1 dose of any vaccine (Johnson & Johnson is not included). **Fully Vaccinated: one dose of Johnson & Johnson or 2 doses of any other vaccine. € Chronic Conditions includes Diabetes - heart disease – Hypertension - Immunodeficiency/organ transplant - lung disease – Asthma – Cancer - renal disease - Liver disease - Rheumatological disease Ω Evidence of previous infection mean the presence of either PCR positive before or at enrollment or Serology positive at enrollment Sinovac: CoronaVac, Sinopharm: BBIB-CorV or WIBP-CorV, AstraZeneca: ChAdOx1 nCoV-19, Moderna: mRNA-1273, Janssen: Ad26.COV2. S, Pfizer: BNT162b2 mRNA. Table (2): Participant Demographics and Clinical Characteristics by Vaccination Status at the Start of Follow-Up Variable © All Participants* Unvaccinated (any vaccine) Partially vaccinated** Fully Vaccinated*** Booster dose P value n= 1230 n= 103 (8.4%) n= 52 (4.2%) n= 900 (73.2%) n= 175 (14.2%) Age Group (Years) 17-30 309 (25.1) 25 (24.3) 26 (50.0) 222 (24.7) 36 (20.6) 50 258 (21.0) 16(5.5) 3 (5.8) 189 (21.0) 50 (28.6) Median IQR 40.0 (30.0-49.0) 36.0 (31.0-44.0) 30.5 (27.0-37.0) 41.0 (31.0-49.0) 43.0 (34.5-51.5) Sex Males 545 (44.3) 44 (42.7) 29 (55.8) 390 (43.3) 82 (46.9) 0.298 Females 685 (55.7) 59 (57.3) 23 (44.2) 510 (56.7) 93 (55.1) Chronic illness No 914 (74.3) 80 (77.7) 45 (86.5) 662 (73.6) 127 (72.6) 0.156 Yes 316 (25.7) 23 (22.3) 7 (13.5) 238 (26.4) 48 (27.4) Vaccine Brand Sinovac 85 (6.8%) 0 (0.0) 6 (11.5) 66 (7.3) 13 (7.4) <0.001 Sinopharm 474 (38.5%) 0 (0.0) 12 (23.1) 414 (46.0) 48 (27.4) AstraZeneca 388 (31.5%) 0 (0.0) 26 (50.0) 322 (35.8) 40 (22.9) Sputnik 1 (0.1) 0 0 (0.0%) 0 (0.0%) 1 (0.6) Moderna 22 (1.8%) 0 (0.0) 3 (5.8) 7 (0.8) 12 (6.9) Johnson and Johnson (Janssen) 11 (0.9%) 0 (0.0) 0 (0.0) 10 (1.1) 1 (0.6) Pfizer 136 (11.1%) 0 (0.0) 5 (9.6) 71 (7.9) 60 (34.3) Heterologous 10 (0.8%) 0 (0.0) 0 (0.0) 10 (1.1) 0 (0.0%) © The percentages reported by column * There are 19 missing participants (14 participants were dropped out just after enrollment (death, retiring, or change of workplace) and 5 dropped out before contribution as person-time at risk (PCR positive at enrollment). ** Partially vaccinated: 1 dose any vaccine (Johnson & Johnson is not included) *** Fully Vaccinated: 2 doses any vaccine, except for Johnson & Johnson (Janssen) only one dose considered fully vaccinated € Chronic Conditions includes Diabetes - Heart disease – Hypertension - Immunodeficiency/organ transplant - Lung disease – Asthma – Cancer - Renal disease - Liver disease - Rheumatological disease Sinovac: CoronaVac, Sinopharm: BBIB-CorV or WIBP-CorV, AstraZeneca: ChAdOx1 nCoV-19, Moderna: mRNA-1273, Janssen: Ad26.COV2.S, Pfizer: BNT162b2 mRNA, Sputnik: Gam-COVID-Vac. IV-3 Laboratory results: At enrollment, SARS-CoV-2 spike-binding antibodies were detected in 1245/1248 (99.8%) of the recruited participants (figure (1) and table (1)). The level was >2500 U/ml in 664/1245 (53.3%) of the recruited HWs, and three samples were negative for SARS-CoV-2 spike-binding antibodies, all of which were from HWs who had completed their primary vaccination series. All unvaccinated HWs (106, 100%) were seropositive. At enrollment, SARS-CoV-2 RNA positivity was detected among 119/1235 (9.5%) HWs. Among the 148 symptomatic HWs, only 13 (8.8%) were SARS-CoV-2 RNA positive, while most SARS-CoV-2 RNA-positive HWs were asymptomatic (106/119–89%). Neither hospitalizations nor deaths were recorded among the recruited participants, table (3). During biweekly follow-up visits within a one-year period, 232 HWs developed symptoms compatible with the COVID-19 case definition, 108 (46.4%) of whom provided nasopharyngeal samples. Among these samples, 18 (16.6%) were SARS-CoV-2 RNA positive, and the peak infection rate was recorded in March 2023. The symptomatic RT‒PCR-confirmed COVID-19 infection, which corresponded to an incidence of 0.44 cases per 10,000 person-days. There were 10(1.1) cases among the fully vaccinated participants, 3(5.8%) among the partially vaccinated participants, 2(1.1) among those who had received a booster dose, and 3(2.9%) among unvaccinated participants (Table 3). Table (3) Description of the Clinical Endpoints of COVID-19 RNA-Positive Participants Total Cohort Vaccination Status at the Time of Onset At Enrollment Total n (%) Unvaccinated n (%) Partially vaccinated* n (%) Fully Vaccinated** n (%) Booster n (%) Total cohort with PCR swab results (14 excluded) 1235 107 51 899 178 All positive PCR 119/1235 (9.6%) 12/107 (11.2%) 4/51 (7.8%) 79/899 (8.8%) 24/178 (13.5%) Symptomatic HWs with positive PCR 13/148 (8.8%) 1/12 (8.3%) 1/5 (20%) 8/110 (7.3%) 3/21 (14.3%) Asymptomatic HWs with positive PCR 106/1087 (9.7%) 11/95 (11.6%) 3/46 (6.5%) 71/789 (9.0%) 21/157 (13.4%) Symptomatic cases with positive PCR required medical care 8/13 (61.5%) 1/1 (100%) 0 4/8 (50%) 3/3 (100%) Symptomatic cases with positive PCR required hospitalization 0 0 0 0 0 Symptomatic cases with positive PCR died 0 0 0 0 0 At End of the Follow Up (Total Cohort 1230 as 19 dropped out before being at risk) Total Followed Up Participants 1230 103 52 900 175 Symptomatic HWs with Positive PCR 18/1230 (1.5%) 3/103(2.9%) 3/52 (5.8%) 10/900 (1.1%) 2/175 (1.5%) Symptomatic HWs with Positive PCR (18) Requiring Medical Care 12 (66.7%) 0 3 (100%) 7 (70.0%) 2 (100%) Symptomatic with Positive PCR Requiring Hospitalization 0 0 0 0 0 Symptomatic HWs with Positive PCR died 0 0 0 0 0 * Partially vaccinated : 1 dose of any vaccine except for Johnson and Johnson. **Fully Vaccinated: one dose of Johnson and Johnson or 2 doses of any other vaccines. IV-4 Vaccine effectiveness IV-4-1 Vaccine effectiveness per number of doses: Full vaccination or booster dose VE against symptomatic PCR-confirmed COVID-19 was not significantly different compared with unvaccinated HWs, with adjusted VE values of 68% (95%CI -28% to 92%) and 64% (95%CI -170% to 95%), respectively, P =0.106 and 0.318 respectively, table (4-A) and figures (4-5). IV.4.2 Vaccine effectiveness per type of vaccine: Thirteen symptomatic HWs had RT‒PCR-confirmed SARS‒CoV-2 infection, three of them being unvaccinated. One, five, and four HWs with RT-PCR confirmed COVID-19 infection were vaccinated with Sinovac, Sinopharm and AstraZeneca, respectively, with adjusted VE% of 65% (95%CI -59% to 92%) and 85% (95%CI: -19% to 98%) for Sinopharm and AstraZeneca, respectively compared to unvaccinated group, P =0.176, and P=0.073 respectively. For Sinovac, as there was only one symptomatic case, so VE could not be calculated, table (4-A) and figures (4-5). Because of the limited number of events, VE was not fully calculated; however, those who had received Pfizer, Moderna, or Johnson and Johnson (Janssen) did not show any breakthrough infections. IV .4 .3 Vaccine effectiveness by prior infection: Among participants with prior infection (total 263), the combined effect of previous infection and vaccination had an adjusted VE of 89% (95% CI: -33% to 99%), with no significant difference detected for unadjusted/adjusted VE among fully vaccination compared to the unvaccinated, P=0.163 and P=0.082 respectively, table (4-B), figures (4-5). IV .4 .4 Vaccine effectiveness by time since vaccination: Among two-dose vaccinated participants, 10/900 developed breakthrough infection, all of whom were detected among those with a duration >365 days from the 2nd dose with an adjusted VE of 68% (95%CI: -25% to 92%) compared with unvaccinated participants, P = 0.113, table (4-C) and figures (4-5). Unadjusted and adjusted VE among participants who had received a booster dose compared with those who had received 2 vaccine doses were not significantly different (P = 0.0875, figure (4-5). Because of limited events, the VE in HWs receiving booster doses against RT‒PCR confirmed that COVID‒19 infection stratified by previous infection status and vaccine type could not be evaluated. IV .4 .5 Sensitivity analysis of vaccine effectiveness The sensitivity analysis revealed nearly similar results for VE after the exclusion of participants with a decrease in the post-infection period at risk for 60 days instead of 90 days, with unadjusted VE values of 65% (95%CI: -27% to 90%), and adjusted VE 68% (95%CL: -29% to 92%), with P value for both =0.111. The unadjusted VE after excluding symptomatic patients who refused to provide nasopharyngeal swabs was 67% (95%CI: -19% to 91%), and the adjusted VE was 69% (95%CL -24% to 92%) with P value for both =0.116. When HWs who had a duration of less than 21 days between receiving the first and second doses of the vaccine were excluded, the unadjusted VE was 64% (95%CI -30% to 90%) and the adjusted VE 67% (95%CL -33% to 92%), with P value for both =0.121, figures (6-7). Table (4): A- Vaccine Effectiveness against Symptomatic PCR Confirmed SARS-CoV-2 Infection according to number of vaccine doses and Vaccine Type Two Doses (All Vaccines) * N Total Person-Time (Days) Symptomatic COVID-19 PCR-Confirmed Infections Incidence /10,000 person-days Unadjusted VE ( 95% CI) P Value Adjusted VE (95% CI) P Value Total cohort 1230 406382 18* 0.44 Unvaccinated 103 29604 3 1.01 Reference ≥14days from 2nd dose 900 305164 10 0.33 65% (-26% - 90%) 0.107 68% (-28% - 92%) 0.106 ≥14days from Booster dose 175 54035 2 0.37 60% (-143% - 93%) 0.323 64% (-170% - 95%) 0.318 By Brand of Vaccine for Total Cohort Total cohort* 1003 334768 13 0.39 - - - - Unvaccinated 103 29604 3 1.01 Reference - - - SINOVAC 66 22343 1 0.45 ISD SINOPHARM 414 138825 5 0.36 60% (-66% - 91%) 0.205 65% (-59% - 92%) 0.176 AstraZeneca 322 110324 4 0.36 63% (-67% - 92%) 0.196 85% (-19% - 98%) 0.073 Total cohort of the unvaccinated were 103 and fully vaccinated were 900 CI: confidence Interval VE: Vaccine Effectiveness ISD: insufficient data to calculate VE *Three symptomatic COVID-19 PCR-confirmed infections were detected among partially vaccinated group and were excluded from the analysis of VE Sinovac: CoronaVac, Sinopharm: BBIB-CorV or WIBP-CorV, AstraZeneca: ChAdOx1 nCoV-19. Table (4): B- Combined Effect of Previous Infection + Vaccination on VE against SARS-CoV-2 Infection (Hybrid Immunity) Two Doses (All Vaccines) N Total Person-Time (Days) Symptomatic COVID-19 PCR-Confirmed Infections Incidence /10,000 person-days Unadjusted VE ( 95% CI) P Value Adjusted VE (95% CI) P Value Total Cohort 263 78825 4 0.51 - - - - Unvaccinated with past infection 102 29268 3 1.03 Reference - - - - ≥14Days from 2nd Dose among fully vaccinated with past infection 161 49909 1 0.20 80% (-92% - 98%) 0.163 89% (-33% - 99%) 0.082 Table (4): C-Two doses Vaccine Effectiveness Against Symptomatic COVID-19 Infection, Incorporating Time Since Vaccination Two Doses (All Vaccines) N Total person-time (days) Symptom. COVID-19 PCR-Confirmed Infections Incidence /10,000 person-days Unadjusted VE ( 95% CI) P Value Adjusted VE (95% CI) P Value Total Cohort 1003 331068 13 0.39 Unvaccinated 103 29604 3 1.01 Reference - - - 14days-≤365Days from 2nd dose 7 486 0 0.00 ISD >365Days from 2nd dose 893 300978 10 0.33 64% (-27% - 90%) 0.113 68% (-25% - 92%) 0.11 CI: confidence Interval VE: Vaccine Effectiveness- ISD: insufficient data to calculate VE DISCUSSION Recognizing the critical importance of leveraging local data to inform national and regional vaccine policies, the WHO-EMRO) provided technical and financial support to four regional countries to conduct SARS-CoV-2 vaccine effectiveness studies(18). Healthcare workers (HWs) faced a significant risk of exposure to SARS-CoV-2 infection, as well as increased morbidity and mortality, while also being at a high risk of transmitting the virus to hospitalized patients, who are often more vulnerable to severe COVID-19 outcomes (25).Thus, the current study was conducted to measure SARS-CoV-2 VE against symptomatic RT‒PCR-confirmed SARS‒CoV-2 infection among HWs eligible for vaccination at Al-Azhar University hospitals. A total of 1249 out of 13260 HWs were recruited from the workforce in the five hospitals distributed among three main governorates in Egypt. Enrollment was conducted between July and August 2022, when almost all HWs were vaccinated with primary vaccination series or by a booster (87.3%), and different types of COVID-19 vaccines were available. Only one participant received the booster dose during the follow-up period. For the overall cohort, vaccinated participants had received their second dose long before enrollment (median of 294.0 days (IQR: 232--387)). Different vaccine brands were introduced in Egypt, and most of them were provided to the studied participants within the study cohort, with high vaccination coverage of 1142/1249 (91.4%). Several online surveys have been conducted in Egypt to study COVID-19 vaccination coverage and population perceptions, and different acceptance rates have been reported among the Egyptian population, ranging from 31.1% to 71.1%(3,14,15,26). An earlier questionnaire-based cross-sectional Egyptian study conducted in 2021 reported 21% vaccine coverage among HWs (27), which increased to 70.5% in a more recent similar study (28). To study VE, unvaccinated participants were used as a reference group. VE against symptomatic RNA-confirmed cases was estimated via Cox proportional hazards regressions adjusted for age, sex, and comorbidities. To avoid bias due to insufficient data for some vaccines or subgroups, VE estimates were not calculated when the total number of HWs with COVID-19 was less than five. In addition, because of the small number of events, VE estimates were often inconclusive after adjustment, likely due to the reduced statistical power. The limited number of events also resulted in significant variability in the outcomes, as evidenced by the broad confidence intervals observed for the VE estimates (25) . According to the FDA-issued guidance, the COVID-19 vaccine efficacy rate should be at least 50% to be considered successful, although the lower bound of the confidence interval can be as low as 30% (29). In the current study, the adjusted VE among the whole study cohort was 68% (95% CI -28% to 92%) for those who completed their primary vaccination series. Similarly, the adjusted VE for participants who completed their primary vaccination series 68% (95% CI -28% to 92%) and those who received a booster dose 64% (95% CI -170% to 95%) showed no significant difference (P>0.05). This is in line with previous studies (30). However, it was previously shown that the booster dose remained effective for four months following vaccination and then declined substantially thereafter (30–32) Inconclusive results with wide confidence intervals were also reported in three other VE studies conducted in three different countries within the region, and this was explained by the increasing challenge of obtaining reliable VE estimates late during the COVID-19 pandemic in the Omicron dominant period. Real-time RT‒PCR has been employed worldwide to detect SARS-CoV-2 due to the minimal likelihood of false positive results (33); however, negative real-time RT‒PCR results do not exclude possible infection. Clerici et al (2021) reported that in 233 patients, the sensitivity of RT‒PCR for the detection of COVID‒19 RNA from NP swabs was 77% (95% CI, 73--81%) (34). Although the analytical performance of RT‒PCR is well accepted, pre-analytical factors cannot be excluded. At enrollment, SARS-CoV-2 RNA was detected among 119/1230 (9.6%) HWs; of those HWs, only 13 (10.9%) were symptomatic. These findings indicate that most COVID-19-positive patients are asymptomatic. However, neither hospitalization nor death was recorded among the recruited participants. This can likely be explained by occurring during the Omicron era, where the Omicron variant and its subvariants had mainly driven infections worldwide, as reported by the WHO (8). It accounted for more than 98% of the publicly available sequences since February 2022 and constituted the genetic background from which new SARS-CoV-2 variants are likely to emerge (35) It is notable that all unvaccinated HWs (107,100%) were seropositive, and 83 (77.6%) did not have RT‒PCR results indicating COVID-19+ infection at enrollment or before enrollment, indicating the presence of asymptomatic infection. According to the CDC, some respiratory viruses, mainly influenza and RSV, share very similar symptoms with COVID-19, which may also explain the negative RNA results for COVID-19 despite symptoms (36). A total of 232 participants developed COVID-19 symptoms during follow up, and only 108 (46.4%) provided a nasopharyngeal sample, of whom 18/108 (16.7%) individuals were SARS-CoV-2 RNA positive, with an incidence of 0.44 cases per 10000 person-days. Among these 18 positive cases, 15/18 (83.3) were vaccinated. A total of 12/18 (66.7%) HWs required medical treatment, but neither hospitalization nor death was recorded among HWs. This was in accordance with the WHO which stated that people can still develop COVID-19 after vaccination but are more likely to have mild or no symptoms (8). Moreover, enrollment of participants occurred during the fifth wave of the COVID-19 pandemic (July and August 2022), which showed a high prevalence of Omicron variants. Compared with the early variants, Omicron variant is associated with a greater rate of transmission, a lower hospitalization rate and case fatality rate (4). A recent Egyptian study revealed that symptoms were reported less often in the omicron cohort than in patients with other variants (15). Importantly, at enrollment, a total of 1245/1248 (99.8%) of the studied participants were seropositive for COVID-19 anti-spike-binding antibodies with levels > 2500 U/ml in 664/1245 (53.3%) of participants. Notably, only three participants (0.3%) had negative binding antibodies despite completing the vaccine doses . Moreover, all unvaccinated participants (107) were seropositive, indicating that they had previously contracted COVID-19 infection. Anti-S and overall SARS-CoV-2-specific IgG remain detectable in approximately 90% of persons who seroconvert up to 10 months to one-year post-infection (37,38). Previous studies have revealed that antibody titers peak within 3–5 weeks following infection and then begin to wane in a manner that varies by individual, target antigen, antibody isotype, and assay used (37,39). A growing body of evidence confirms that the COVID-19 vaccine is important for preventing severe infection, hospitalization and mortality. This is in accordance with the current study, where most HWs were vaccinated and none of the HWs who experienced breakthrough infection needed hospitalization or died. Additionally, the CDC has confirmed that higher antibody titters are associated with a decreased risk of subsequent symptomatic SARS-CoV-2 infection (40). When the binding antibody titers were evaluated in breakthrough infection, with SARS-CoV-2 after two or more doses of the vaccine, it was shown that those with breakthrough infection already had antibody titers of tens of thousands of U/mL. This can be related to “hybrid immunity” after spontaneous infection following two or more doses of the vaccine (4). Most people with COVID-19 infection develop detectable anti-SARS-CoV-2 antibodies, with seroconversion rates of 90% or higher (41,42). CDC reported that the immunity provided by vaccines and prior infection is high but incomplete (40). Post-infection antibodies target the spike (S) protein, receptor binding domain (RBD) of the spike protein and nucleocapsid (N) core protein; meanwhile, vaccination induces the production of (S) and anti-RBD binding and neutralizing antibodies in the blood but not anti-N antibodies (40).If breakthrough infections are frequent, severe, or highly transmissible, there may be a need for additional vaccine doses, adjustments to vaccine formulations, or non-pharmaceutical interventions (or a combination of these strategies) to decrease the rate of infection(X8). When the full cohort was stratified by previous infection status for full dose(s) vaccinated participants who had RT‒PCR- SARS-CoV-2 confirmed infection prior to or at enrollment (hybrid immunity), the adjusted two-dose VE vs the unvaccinated increased to 89% CI (-33%-99%) (P>0.05). Notably, the cumulative incidence of COVID-19 breakthrough infections was significantly higher among those who were partially vaccinated compared to those who were unvaccinated or those who received two or three doses of the vaccine ( p <0.05). This may be due to natural immunity, where all unvaccinated HWs reported previous SARS-CoV-2 infection either before or at enrollment, as detected by RT‒PCR, whereas the rates of previous SARS-CoV-2 infection among HWs with partial vaccination, those who received a full primary series or a booster dose were 11.8%, 18.2% and 18%, respectively. Previous studies have shown that the immune response following infection continues to provide at least 50% protection against reinfection for 1–2 years following initial infection with SARS-CoV-2 (43,44). Additionally, in a study among HWs vaccinated 7–11 months after infection with COVID-19, the antibody titers measured 6 days after their first dose were twice as high as the antibody titers measured one month after their initial infection. Moreover, they were able to neutralize different COVID-19 variants, irrespective of vaccine type, number of doses, or pre-vaccination antibody titers (45). A recent systematic review on measuring the magnitude and duration of hybrid immunity against severe disease and infection caused by the Omicron variant revealed that individuals with hybrid immunity had greater magnitude and durability of protection than individuals who had no history of previous infection (46). It is worth noting that prior SARS-CoV-2 infection lowered the risk of re-infection, even without vaccination. The current findings, which show the protective effect of infection alone during the pre-Omicron period, have also been observed in other studies(25). In the studied cohort, only seven HWs were 14–365 days from the 2nd dose; none of them developed COVID-19 symptoms during follow-up, whereas all other HWs were >365 days from their completion of the primary vaccination series. The adjusted VE was 68% (CI -25%-92%) among HWs vaccinated vs the unvaccinated, P > 0.05. A recent study indicated rapid waning of the booster dose with increased time from vaccination (47). A model linking immunity levels and protection to VE data from England for three vaccines (Oxford/AstraZenecaAZD1222, Pfizer-BioNTech BNT162b2, Moderna mRNA-1273) and two variants (Delta, Omicron) projected gradual waning to moderate protection after 1 year(48). The current study could not show a significant effect of a booster dose. A recent European study showed that VE waned 12 weeks after vaccine administration and decreased even further after 24 weeks (30). It has also been shown that the time since the last booster dose is more important than the total number of doses administered for protection against severe COVID-19 (49). On the other hand, when VE is evaluated in relation to the vaccine brand, limited infection events did not allow VE estimation among HWs in the study cohort. However, there was no significant difference between each vaccine type and the unvaccinated group (P > 0.05). The VE of all the vaccines decreased over time, implying that, to reach herd immunity, booster shots are needed. VE was higher in mRNA vaccines than in the other vaccines, as no breakthrough infection was recorded among HWs receiving the Pfizer or Moderna vaccines, whereas the adjusted VE for AstraZeneca was 85%, 95% CI (-19% - 98%), and that of Sinopharm was 65%, 95% CI (-59% - 92%), indicating a lower VE for inactivated vaccines than for the mRNA vaccines; however, because there were few or no events, VE for Sinovac could not be calculated. This finding is in line with other studies (50). Of note, the relative VE of the 3rd dose against RT‒PCR-confirmed COVID‒19 infection, stratified by previous infection status and vaccine type, could not be calculated due to insufficient data and limited events. Sensitivity analysis revealed similar results, with the exclusion of participants who had durations < 21 days, durations between the 1 st and 2 nd doses, or symptomatic patients who refused to have their nasopharyngeal swabs taken or whose disease duration decreased to 60 days instead of 90 days. With respect to the 8% of unvaccinated HWs, it is well known that despite worldwide measures to ensure that COVID-19 vaccine use was affordable, accessible, and beneficial to the community, vaccine hesitancy among Egyptians was / is an issue of concern (15). COVID-19 vaccine refusal was multifactorial in these studies and was attributed mainly to doubts about vaccine effectiveness, a lack of trust due to rapid vaccine production, inadequate information, and a fear of vaccine side effects. As emphasized by Kandeel et al. (2023), Egypt being a low- and middle-income countries (LMIC), still faces considerable obstacles in receiving, distributing, and accepting vaccinations at the community level (4). Limitations: Some limitations were encountered, such as starting the study in the pandemic declining phase, during which too few infections occurred and that may have affected VE estimates. Low-event VE estimates emphasize the importance of sample size, and the small number of cases often yielded inconclusive results. Only 109/232 nasopharyngeal swab samples were available from the follow up for evaluation. Excluding follow up of asymptomatic participants, who presented the main COVID-19 infection status at that time of Omicron dominance, is also a limitation that must be considered. The use of up to six vaccine brands, together with a small sample size, provided insufficient data that did not allow calculation of vaccine-specific VEs. The lack of viral genetic sequence data for the study of circulating virus variants and the lack of detection of anti-N antibodies to differentiate between immunity due to vaccination only or infection-induced immunity are issues of concern. Conclusions This is the first HW cohort multicenter study conducted in Egypt to estimate VE among HWs. While the overall VEs demonstrated protection against symptomatic disease, the few events reported during follow-up limit the study’s statistical power, and most estimates were inconclusive. However, the point estimates and crude VE estimates may support the importance of completing the primary vaccination series against COVID-19. This study’s results could provide a platform for conducting and evaluating COVID-19 VE studies in the future that will help decision makers in devising / formulating vaccine policies at the national and regional levels and better understand the disease burden and effects of adopted vaccination policies. It could also provide evidence on implementation challenges and feasibility, underscoring how future immunization agenda must be driven. Many inquiries still need answers, such as the optimal number of booster doses, duration of protection, and vaccine adverse events. The study of COVID-19 variants is still essential for evaluating vaccine effectiveness, as mutations in the spike protein of variant(s) of interest could impair the binding ability of the antibodies. DECLARATIONS Ethics approval and consent to participate: The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of Al-Azhar University on 5/12/2021 (AU-REC-2021-0002). Informed written consent was provided by each participant. Clinical trial number : Not applicable. Consent for publication: No individual person’s data in any form is included, where each participant was allocated a unique study ID number- using a barcode-at enrollment. Informed written consent was provided by each participant. Availability of data and material The data presented in the manuscript is shared with WHO regional office. Requests to access any datasets or codes/scripts used for data analysis should be directed to the corresponding author, whenever reasonable. Competing interests No competing or conflicting interest are declared. This study received full technical and financial support from the WHO Regional Office for the Eastern Mediterranean. WHO registries file number: 2022/1276447- Funding: This research received funding/financial support from the World Health Organization (WHO) for the duration of the study (September 2021–April 2024). WHO Regional Office for Eastern Mediterranean Region (EMRO) Authors' contributions: SZN and SII are the PI and Co PI of the project, both responsible for designing research idea and developing the research question and rationale, conceptualization and methodology. They conducted literature review, results interpretation and manuscript editing. KZ, KM, FK and RA are the WHO partners, who shared in conceptualization, methodology, validation, supervised the project implementation and provided technical support. They also critically revised the final manuscript draft. ZS, EAA, ESS, EF, and EAK are the leaders of the five University hospitals’ team, who were responsible for HWs recruitment and monitoring their follow up. Sumaya H. ESH, EE, ENA, EA, AN, MS, AAA, AEA, KAS, SMA, EAM, BIM, HMM, GAM, AWO, EAW, HMA, Amro M. HAM, AE, MAQ, AOM, SSS were responsible for HWs’ sampling, data collection and follow up. RA, GA, KA, and EAM are responsible for conducting molecular techniques for detection of SARS COV-2 RNA, communication with the hospitals’ team, preparing participants ’files’ for NRC team and manuscript draft writing. MS, AA, ABW, SMA and BIM are engaged in SARS-CoV-2 antibody detection. SSI, EGA, ADE, HHM, ESE, SR and ED were responsible for data entry, data management and statistical analysis.SM, as the University vice president supervised the project implementation and facilitated any administration constrains. All the authors have seen and agreed to the submission of the manuscript and their inclusion of name(s) as co-author(s). Acknowledgements : Thanks, and appreciation to the WHO Regional Office for Eastern Mediterranean and the WHO country office in Egypt for the resources provided that enabled the successful execution of this project. We acknowledge the WHO knowledge and expertise that contributed significantly to the project’s success. The extraordinary contributions of the WHO and continuous support greatly improved the quality of this study. The authors are also grateful to Giulio Borghi, Manuela Runge, and Carsten Mantel, MMGH Consulting, Zurich, Switzerland, for helpful input during the initial analysis and presentation of the results. REFERENCES Egypt COVID - Coronavirus Statistics - Worldometer [Internet]. [cited 2024 Aug 19]. Available from: https://www.worldometers.info/coronavirus/country/egypt/ Beginning of the end of coronavirus? - Egypt - Al-Ahram Weekly - Ahram Online [Internet]. [cited 2024 Aug 19]. 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COVID-19 Living Evidence Synthesis 10.14 - What is the long-term effectiveness of available COVID-19 vaccines for adults, including for variants of concern and over time frames beyond 112 days in those with a primary series and beyond 84 days in those with a primary series and an additional dose? [Internet]. Available from: https://www.mcmasterforum.org/docs/default-source/product-documents/living- Hogan AB, Doohan P, Wu SL, Mesa DO, Toor J, Watson OJ, et al. Estimating long-term vaccine effectiveness against SARS-CoV-2 variants: a model-based approach. Nat Commun. 2023 Dec 1;14(1). Interim analysis of COVID-19 vaccine effectiveness against hospitalisation and death using electronic health records in six European countries [Internet]. [cited 2024 Aug 19]. Available from: https://www.ecdc.europa.eu/en/publications-data/interim-analysis-covid-19-vaccine-effectiveness-against-hospitalisation-and-death Robles-Fontán MM, Nieves EG, Cardona-Gerena I, Irizarry RA. Effectiveness estimates of three COVID-19 vaccines based on observational data from Puerto Rico. The Lancet Regional Health – Americas [Internet]. 2022 May 1;9. Available from: https://doi.org/10.1016/j.lana.2022.100212 Additional Declarations Competing interest reported. This study received full technical and financial support from the WHO Regional Office for the Eastern Mediterranean. WHO registries file number: 2022/1276447. 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06:31:44","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":209159,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCumulative COVID-19 vaccine coverage among study participants by epidemiological month and year\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5754076/v1/9a7cd76311378ae97804f1bb.jpeg"},{"id":79550356,"identity":"9a7039bc-55a5-4056-9458-d33dc8039472","added_by":"auto","created_at":"2025-03-31 06:31:44","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":185414,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSurvival Curve and Person-Time at Risk\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5754076/v1/2768e6f762842cc09edf7544.jpeg"},{"id":79550351,"identity":"6da0e057-3bf9-491f-8bf8-f3608f09b0e1","added_by":"auto","created_at":"2025-03-31 06:31:44","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":17886,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eUnadjusted VE (%) against RT‒PCR-confirmed symptomatic infection\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-5754076/v1/5f9cb32584d7eca01f9c79c9.png"},{"id":79551442,"identity":"13e4198f-aa32-4bfa-97f0-e1c30e4299f6","added_by":"auto","created_at":"2025-03-31 06:39:44","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":16914,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAdjusted VE (%) against RT‒PCR-confirmed symptomatic infection\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-5754076/v1/54ab993b109466be19eb5ce6.png"},{"id":79550365,"identity":"f2f30cd8-e195-403a-af88-d422c54fe73c","added_by":"auto","created_at":"2025-03-31 06:31:45","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":14469,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eUnadjusted VE (%) against RT‒PCR-confirmed symptomatic infection (sensitivity analysis)\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-5754076/v1/5352aecf16a0f209fd20c211.png"},{"id":79550362,"identity":"e3ba3139-d675-4877-be41-073f4cfe9177","added_by":"auto","created_at":"2025-03-31 06:31:44","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":14600,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAdjusted VE (%) against RT‒PCR-confirmed symptomatic infection (sensitivity analysis)\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-5754076/v1/a23adcd768953db89453af89.png"},{"id":92430642,"identity":"395cccf4-70b1-4d6a-adba-b053777a0eec","added_by":"auto","created_at":"2025-09-29 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This study received full technical and financial support from the WHO Regional Office for the Eastern Mediterranean. WHO registries file number: 2022/1276447.","formattedTitle":"Assessing SARS-CoV-2 Vaccine Effectiveness in Health Workers: A Cohort Study in Five Al-Azhar University Hospitals, Egypt","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eThe worldwide emergence of severe acute respiratory syndrome (SARS) caused by SARS-CoV-2, which is commonly known as coronavirus disease 2019 (COVID-19), has presented a significant challenge and a global public health concern. The severity of COVID-19 spans from asymptomatic infection to critical illness, resulting in fatalities, as reported by the World Health Organization (WHO). In September 2023, there were 770,875,433 confirmed cases of SARS-CoV-2, including 6,959,316 deaths globally, 23,394,122 confirmed cases in the Eastern Mediterranean and 9,569,874 in Africa, with cumulative cases of 516,023 and 24,830 deaths in Egypt (1) . Egypt reported its first case on 14/3/2020; then experienced five waves of COVID-19 until the end of May 2022, the fifth wave starting in the first week of 2022 and lasting for 16 weeks (2,3). By the beginning of the fifth wave, Omicron was the dominant SARS-CoV-2 variant in Egypt (4).\u003c/p\u003e\n\u003cp\u003eSince the\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eWHO declaration of the global pandemic of COVID-19 in March 2020(5), several types of vaccines against COVID-19 have been rapidly developed worldwide and recent studies have confirmed safety and effectiveness of these vaccines(6,7). As of May 2023, a total of 13,505,262,477 vaccine doses\u0026nbsp;were administered(8) . Vaccination against SARS-CoV-2 is a leading strategy to change the course of the COVID-19 pandemic, as different types of COVID-19 vaccines are available worldwide. Each vaccine exhibits a different potency and duration of efficacy, as determined by the antigen design, adjuvant molecules, vaccine delivery platforms, and immunization method(9). The CDC assesses vaccine effectiveness through multiple observational studies that utilize various methods and uses data gathered from surveillance platforms, electronic health records, and prospective studies. These studies have demonstrated that VE is influenced by several factors including host-related factors (age, chronic illness, and history of previous infection), viral factors like circulating variant(s), vaccine related factors such as vaccine type and time since vaccination, the total number of doses received, and the duration since the most recent dose (10). A systematic literature review and meta-analysis on the effectiveness of COVID-19 vaccination against post-COVID conditions (long COVID) among fully vaccinated individuals showed that completed COVID-19 vaccination prior to being infected resulted in a significant decrease in long COVID throughout the study period. Vaccine effectiveness demonstrated an increase when booster doses were administered (11)\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eEgypt introduced different types of vaccines, including inactivated vaccines such as CoronaVac\u0026reg; (Sinovac) and Covilo\u0026reg; (Sinopharm), Beijing; adenovirus vector vaccines such as Vaxzevria\u0026reg; (Oxford/AstraZeneca), Sputnik V\u0026reg; (Gamaleya Institute) and Jcovden\u0026reg; (Janssen); and mRNA vaccines such as Comirnaty\u0026reg; (Pfizer/BioNTech) and Spikevax\u0026reg; (Moderna) (12). Additionally, the Egyptian Holding Company for Biological Products and Vaccines (VACSERA) started producing doses of China\u0026apos;s Sinovac SARS-CoV-2 vaccine. Stability studies on this vaccine were conducted, and it was administered to Egyptian citizens starting in August 2021\u0026nbsp;(13). Egypt started its COVID-19 vaccination rollout campaign on 24 January 2021 for medical personnel and began targeting individuals with chronic diseases and elderly individuals in March 2021. By the end of December 2023, 56% of the Egyptian population had been vaccinated with at least one dose, 41% had completed the primary vaccination series, and 15% had received at least one booster dose\u0026nbsp;(14).\u0026nbsp;A large-scale national survey of 18000 subjects was conducted by the Ministry of Health and Population from March\u0026ndash;May 2022 in Egypt to determine COVID-19 vaccine coverage, which was low (48%) compared with the WHO 70% target (15).Thus, it is crucial to continuously evaluate and obtain updated effectiveness estimates of available vaccines against the prevalent strains of SARS-CoV-2. Real-world\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003evaccine effectiveness (VE) studies can answer questions about effectiveness against transmission or disease outcomes by age group and risk factors, the duration of vaccine protection relative effectiveness of different vaccines, the relative effectiveness of one dose \u003cem\u003evs.\u003c/em\u003e two doses or more, as well as the effectiveness of the vaccine against new viral strains. Healthcare workers (HCWs) are at increased risk of SARS-CoV-2 exposure due to frequent contact with infected patients (16). A\u003cspan dir=\"RTL\"\u003e\u0026nbsp;\u003c/span\u003eWHO sponsored multi-country case-control study conducted between August 2019 and November 2021 across 62 health facilities in 16 countries (1213 cases and 1844 controls) found prolonged patient contact (\u0026lt;\u0026nbsp;1 meter distance for \u0026gt;15\u0026nbsp;mins) significantly increased the likelihood of SARS-CoV-2 infection (OR 1.4; 95% CI 1.0\u0026ndash;1.8)(17). Notably, following the COVID-19 pandemic, there were fewer VE studies from the Eastern Mediterranean Region (EMR) due to limited research infrastructure, expertise, and financial constraints. In response, from 2021 to 2023, the Eastern Mediterranean Regional Office of the World Health Organization (WHO-EMRO) provided technical, organizational, and financial support to enhance local research capacities and inform vaccine policies for the region. Four EMR countries \u0026ndash; Egypt, Jordan, Iran, and Pakistan \u0026ndash; were selected to participate, utilizing two WHO protocols: a cohort study among healthcare workers and a test-negative design at severe acute respiratory infection surveillance sites(18). WHO-EMRO conducted both general and country-specific workshops to build capacity in participating countries, developed tailored questionnaires uploaded to a centralized data platform (REDCap) to streamline data collection, and offered ongoing technical assistance for data quality checks and analysis to investigators. This approach enabled countries to independently analyze national VE data while facilitating pooling of data across countries and reporting regional VE estimates to inform vaccine policies. Thus, the aim of this study was to measure SARS-CoV-2 vaccine effectiveness (VE\u003cs\u003e)\u003c/s\u003e among HWs eligible for vaccination at Al-Azhar University hospitals against symptomatic RT‒PCR confirmed SARS-CoV-2 infection.\u003c/p\u003e"},{"header":"SUBJECTS AND METHODS","content":"\u003cp\u003e\u003cstrong\u003eIII-1-1\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eStudy Setting\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA hospital-based prospective cohort study was carried out with support from the WHO at five university hospitals affiliated with Al-Azhar University, Egypt, focusing on HWs. Three of these hospitals are located in the Cairo governorate (representing the capital), one in the Damietta governorate (representing Lower Egypt), and one in Assuit governorate (representing Upper Egypt). The WHO\u0026rsquo;s protocol, design, and methodology for assessing COVID-19 vaccine effectiveness were customized to suit the specific context and settings of the country.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eII-1-2 Study Participants\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHWs affiliated with Al-Azhar University Hospitals were randomly selected, regardless of their COVID-19 vaccination status. All categories of health workers at these hospitals were eligible for inclusion in the study, provided informed consent was obtained. The study participants included all health workers who interact with patients, handle their body specimens, or manage potentially infectious waste. This included physicians, nurses, emergency medical personnel, laboratory technicians, and administrative staff. To participate, health workers had to be eligible for vaccination and have no contraindications to receiving the COVID-19 vaccine. \u0026nbsp;The number of participants from each facility was estimated according to its total workforce size at each hospital: 300 participants from each hospital in Cairo, 200 from the hospital in Damietta, and 150 from the hospital in Assuit, with the total work force being 13260 HWs in the five hospitals.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eII-1-3 Sampling Criteria\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eStratified Random Sampling: Healthcare workers at each university hospital who consented to participate in the study, regardless of their COVID-19 vaccination status, were categorized into strata based on factors such as age group, gender, and job type. Inclusion criteria comprised all HWs affiliated with Al-Azhar University Hospitals irrespective of their vaccination status or prior infection. HWs who had already been vaccinated against COVID-19 as part of the routine COVID-19 vaccine rollout could be included, if detailed information about their vaccination was available. Exclusion criteria included HWs who were not eligible for COVID-19 vaccination (sever allergy, pregnancy, etc.), or those who refused to sign the informed consent.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eII-1-4 Participant enrollment and follow-up procedures\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study objectives were communicated to HWs at the participating hospitals. The research team informed them about the importance of the study and the benefits of participation, including receiving their lab results. Participation was voluntary, with informed consent required, and participants could withdraw at any time without penalties, though they were asked to notify the team if they chose to do so. Enrollment took place from July to August 2022, and HWs who were ineligible for vaccination (due to factors like severe allergies or pregnancy) or who did not provide informed consent were excluded.\u003c/p\u003e\n\u003cp\u003eParticipants completed a face-to-face interview to complete a questionnaire after signing informed consent. All participants were interviewed and filled out an enrollment questionnaire that includes demographic, clinical, and epidemiological information, vaccination history, as well as occupation- and community-related behaviors.\u0026nbsp;Regular ZOOM meetings were held to ensure proper study implementation at each hospital and monitor adherence to the study protocol by the team\u003cstrong\u003e.\u0026nbsp;\u003c/strong\u003eParticipants\u0026rsquo; self-reported vaccination status was verified through sources such as occupational health records, vaccination cards, or vaccine registries. The Ministry of Health and Population (MOH\u0026amp;P) provided each vaccine recipient with a card detailing their vaccine information, and vaccines were distributed to the university hospitals through a cold chain system. Participants were registered online [\u003cu\u003ehttp://www.egcovac.mohp.gov.eg\u003c/u\u003e], and each participant who consented to take the vaccine had to fill out an application form. Participation was voluntary, the vaccine was free of charge, and vaccination was postponed for 3 months for those who had a recent COVID-19 infection. Participation was encouraged through a national advertising campaign. Samples were transported to the Virology Laboratory, Microbiology Department, faculty of Medicine-Al-Azhar University and stored at -80\u0026deg;C for evaluation of the presence of SARS-CoV-2 RNA via real-time RT‒PCR, whereas the serum samples were transported to clinical pathology laboratories and stored at -20\u0026deg;C \u0026nbsp;at Al-Zahraa, Al-Hussein and Bab-AlSharia hospitals for SARS-CoV-2-binding antibody quantitation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFollow-up phase: participants in each hospital were grouped (20-25) for each investigator, who had a list of his or her assigned participants\u0026rsquo; phone numbers. Participants were monitored biweekly by investigators, who contacted them via phone calls or WhatsApp to complete follow-up questionnaires. Regular reminders were sent before follow-up appointments. In case of COVID 19 symptoms, the investigator examined the participant in the hospital and took a nasopharyngeal swab if indicated. The objective of the follow-up was to:\u0026nbsp;\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003e\u0026nbsp;Identify among the cohort of participant HWs new cases,\u003c/li\u003e\n \u003cli\u003e\u0026nbsp;Track changes in vaccination status,\u003c/li\u003e\n \u003cli\u003e\u0026nbsp;Monitor changes in potential exposures.\u0026nbsp;\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eIf participants exhibited COVID-19 symptoms, a nasopharyngeal swab was taken, and those who failed to respond within 48 hours were contacted again via an alternative method of communication (phone call or WhatsApp message) or visiting them at their workplaces, if they declined to continue, their reasons were documented. Nasopharyngeal swabs were taken within 24\u0026ndash;48 hours from participants suspected of infection who had a history of contact with COVID 19 patients and met the following WHO COVID 19 case definition; acute onset of fever and cough OR acute onset of any three or more of the following symptoms in the previous 7 days: fever, cough, general weakness/fatigue, headache, myalgia, sore throat, coryza, dyspnea, anorexia/nausea/vomiting, diarrhea, altered mental status, anosmia, or ageusia (19). The investigator in each group was responsible for taking the nasopharyngeal swab. Samples were sent directly or stored at -20\u0026deg;C for a few days and then transferred to the virology lab in Cairo for analysis. \u0026nbsp;Those who refused testing were considered dropouts, and their data were recorded as missing. All follow-up interactions were documented using standardized written records to ensure consistency in data collection. The follow-up questionnaire was completed, and the data was collected in Excel sheet, with a copy delivered to the project manager. At the end of the study, 1230 HWs completed the biweekly follow-up, with 14 excluded due to dropout after enrollment (death, retirement, or a change of workplace). \u0026ldquo;Breakthrough infections\u0026rdquo; is a term used to describe infections in fully vaccinated people, while \u0026ldquo;non-breakthrough infections\u0026rdquo; refers to infections in unvaccinated people, who, apart from their vaccination status, are similar to the vaccinated (20).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII-1-5 Data Collection Procedures\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe WHO provided financial and technical support for methodology, data management, report development and statistical analysis of the data (21,22)\u003c/p\u003e\n\u003cp\u003eThe data collection forms were based on the WHO protocol and relevant questionnaires (23). Five questionnaire forms were included, each customized to fit the study requirements. The enrollment questionnaire captured data on demographics; clinical and epidemiological information; comorbidities; working conditions; social activities; community-related behaviors; COVID-19 prevention; and previous history of SARS-CoV-2 infection and COVID-19 vaccination. The laboratory questionnaires (serology/virology) included dates, types of specimens, tests and results, while pre-enrollment and follow-up questionnaires were also included.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIII-2 \u003cem\u003eSample size calculation:\u003c/em\u003e\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe sample size was calculated based on Table 2 in the WHO protocol (24) Assuming a vaccine effectiveness of 60% and that 20% of unvaccinated HWs would be infected with SARS-CoV-2 over a period of 12 months and vaccination coverage among HWs of 90%, the required minimum sample size of 1006 participants was calculated. Accounting for an expected 20% loss to follow-up during the one-year follow-up period, 1250 participants ultimately needed to be included.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIII-3 Ethical considerations:\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEach participant was allocated a unique study ID number with a barcode at enrollment which was scanned at all subsequent steps to identify each respective individual\u0026rsquo;s documents and test. Name and national ID number were included in study databases. Personal identifying information was maintained only by the person responsible (s) in each study site in accordance with regulatory agencies requirements. To ensure confidentiality,\u0026nbsp;anonymization techniques were implemented by removing sensitive data including personally identifiable information, implementing safeguards against participant identification during data entry.\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIII-4 Laboratory Investigations:\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIII-4-1 Detection of SARS-CoV-2 binding:\u003c/em\u003e\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTotal antibodies against the receptor binding domain (RBD) of the S protein were detected in serum samples collected at enrollment via the Roche Elecsys Anti-SARS-CoV-2 S immunoassay on a Roche Cobas e 411 (Roche Diagnostics, GmbH, Germany). The limits of the blank (LoB) and limit of detection (LoD) were 0.30 U/mL and 0.40 U/mL, respectively. Test results \u0026lt;0.8 U/mL were classified as nonreactive, whereas those \u0026ge;0.8 U/mL were classified as reactive. The upper limit of the kit was 250 U/ml, and due to a high number of positive samples that were out of range, all samples were diluted 1:10 to obtain values \u0026le;2500.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIII-4-2 Real-time RT‒PCR:\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eReverse-transcriptase polymerase chain reaction (RT‒PCR) for SARS-CoV-2 was performed using real-time RT‒PCR for samples collected at enrollment and for all symptomatic participants who met the WHO suspected case definition. The detection of SARS-CoV-2 RNA was performed via real-time PCR via a qualitative real-time RT‒PCR kit (the\u0026nbsp;artus\u0026reg;\u0026nbsp;SARS-CoV-2 Prep and Amp UM Kit -QIAGEN-Germany) targeting 2 viral genes (N1 and N2 of the N gene were detected through the same fluorescence channel). The two targets were not differentiated, and amplification of either or both targets led to the generation of fluorescence signal genes. The sample preparation and detection steps were integrated into a single kit\u003cspan dir=\"RTL\"\u003e\u0026nbsp;\u003c/span\u003ewith a limit of detection of 950 cp/ml. A sampling control (RNase P) and internal RNA control, together with positive and negative external controls, were included. Invalid results were obtained for a noticeable number of samples. Thus, RNA extraction (QIAamp DSP Virus spin kit) was performed for invalid samples, where a larger sample volume was tested (200 \u0026micro;l instead of 10 \u0026micro;l), adequate extraction and purification of viral RNA by enzymatic lysis and mixing (protease +buffer AL with carrier RNA), and then RT‒PCR steps with the\u0026nbsp;artus\u0026reg;\u0026nbsp;SARS-CoV-2 Prep and Amp UM Kit were conducted (bypassing its extraction step). The results were conclusive.\u003cstrong\u003e\u003cem\u003e\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIII-5 Statistical Analysis:\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData entry into the REDCAP program occurred under the guidance and support of the WHO-EMRO technical team. Participant\u0026rsquo;s name, address, phone, and mobile number were excluded, as this information was kept only with the follow-up team.\u003c/p\u003e\n\u003cp\u003eStatistical analysis was carried out using SPSS for Windows, version 23. Categorical variables were presented as numbers and percentages, and continuous variables as medians and IQRs. Different statistical methods were used to assess the significance level for the differences between the study groups according to their vaccination status. Chi-square was used to detect the significant difference between categorical variables, and Fisher\u0026rsquo;s exact test was used if the expected number was below 5 in any cell. For continuous variables, one-way ANOVA was used for parametric data and the Kruskal-Wallis test for non-parametric data. Survival analysis was carried out using the Kaplan-Meier test, and a curve was generated to inspect the cumulative incidence according to vaccination status.\u003c/p\u003e\n\u003cp\u003eThe primary outcome, primary series vaccine effectiveness (VE) was estimated against COVID-19. COVID-19 case was defined as a positive PCR result in a symptomatic participant with symptom onset within 14 days prior to the follow up interview. Vaccine effectiveness percent (VE%) was estimated using Cox regression proportional hazards models; hazard ratios comparing vaccinated and unvaccinated were estimated with vaccination as a time-varying exposure. VE% = 1 \u0026ndash; hazard ratio [HR]* 100, where the HR = Exp (B) in the Cox regression model. Follow-up time was from baseline to the time of symptomatic SARS-CoV-2 confirmed with positive PCR or study exit. \u003cstrong\u003eThe 95% CI of VE was computed based on the 95% CI of the HR in the Cox regression.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSubgroup analyses by vaccination doses (partial, fully vaccinated, and booster dose \u003cem\u003evs\u0026nbsp;\u003c/em\u003eunvaccinated; different vaccine type \u003cem\u003evs\u003c/em\u003e unvaccinated; then fully vaccinated \u003cem\u003evs\u003c/em\u003e unvaccinated and vaccine type regarding the prior infection) were performed. For VE calculation, prior infection depends on RT-PCR positivity, either before or at enrollment, or positive serology at enrollment for unvaccinated participants. However, for prior infection, 15 participants were excluded when calculating the VEs, as 14 of them had missing RT-PCR results at enrollment (7 sample results were inconclusive / invalid and 7 were dried samples) and one missing a serology sample. These missing PCR results were at random, from different\u003cem\u003e\u0026nbsp;\u003c/em\u003ehospitals.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAn additional analysis was planned to stratify VE% estimates by time since vaccination, e.g., 14-89 days, 90-179 days, and \u0026gt;=180 days. Follow-up was identified from the start of being at risk to the earliest of outcome or study exit. However, the median duration from receiving the 2nd dose till the end of follow-up was 631 days (IQR: 557-730 days), and between the booster dose and the end of follow-up was 394 days (IQR: 319-491 days). Thus, we only stratified the duration into \u0026lt;=365 days and \u0026gt;365 days.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConfounding factors and effect modifiers\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBoth unadjusted and adjusted estimates of VE were presented. Adjustment was made in the Cox regression model for potential confounders (age, sex, chronic comorbidities, and health facility). Hospitals were categorized in two: Cairo hospitals (Al-Zahraa, Al-Hussein, and Bab-Alsharia) and peripheral (Damiatta and Assuit). Adjustment was made in the multivariable cox regression model for all potential confounders. None of these variables were significant when multivariate Cox regression backwards Wald analysis was done. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSensitivity analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSensitivity analyses were performed to estimate the robustness of the VE estimates produced in the main analysis against different assumptions (e.g., assumptions made on missing data) and/or sources of bias (e.g., the effect of unmeasured confounding factors).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBased on the assumptions made and on the different sources of bias identified, different sensitivity analyses were performed:\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e● Excluding participants with shorter than expected vaccination intervals between the 1st and 2nd dose and including those with \u0026lt;21 days between the first and second dose of vaccine.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e● Consider being at risk after 60 days after previous infection detected by PCR \u003cem\u003eversus\u003c/em\u003e 90 days.\u003c/p\u003e\n\u003cp\u003e● Exclusion of symptomatic patients who refused to give nasopharyngeal swabs \u003cem\u003eversus\u0026nbsp;\u003c/em\u003eincluding them in the VE% estimation.\u003c/p\u003e"},{"header":"RESULTS","content":"\u003cp\u003eOut of the 13260 HWs, 1249 were recruited into the study and agreed to be followed up biweekly for a period of one year. At enrollment, most of the included HWs, 911/1249 (72.9%), had completed the primary vaccination series (one dose of Johnson and Johnson vaccine or two doses of any other vaccine), 179 had received a booster dose (14.3%), 52 were partially vaccinated (4.2%) with one dose, and 107 (8.6%) were unvaccinated. At enrollment, COVID-19 RT‒PCR was performed for 1235 (98.8) participants, with 14 samples excluded (missed, dried or inconclusive results). There were 148 (11.95) symptomatic cases among the 1235 HWs at enrollment, 13 (8.8%) of whom had COVID-19-positive results. COVID-19-binding antibody titters were measured in 1248 HWs with one missing value. A total of 1230 HWs were followed up for 1 year, while 14 (1.1%) participants dropped out just after enrollment and 5 (0.4%) dropped out before contribution as person-time at risk (within 90 days from the date of PCR positive at enrollment). Out of 1230 participants, 232 (18.9%) experienced symptoms, but only 108 (46.4%) agreed to provide nasopharyngeal samples. Out of them, 18 had PCR positive (16.7%), figure (1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIV-1 Baseline characteristics:\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;The cumulative COVID-19 vaccine coverage among the study participants is shown in Figure (2).\u003c/p\u003e\n\u003cp\u003eTheir vaccination started in January 2021 and continued until August 2022. Notably, all vaccinated participants completed their primary vaccination series (full doses) before enrollment, except one, who received his / her booster dose one month after enrollment and during the follow-up period. Demographic and clinical characteristics by vaccination status at enrollment are presented in Table (1). More than half of the recruited HWs were females (697, 55.8%), and the median age was 40.0 (30.0--49.0) years, with half of the partially vaccinated HWs between 17 and 30 years old and 43.9% of the unvaccinated HWs in the age group 31\u0026ndash;40 years. Those who had completed a primary vaccination series or had a booster dose showed nearly equal age group distributions. Most of the participants were nurses, 536 (42.9%), with other HW categories, including physicians, technicians, admins and workers. Overall, most HWs were healthy, with 927 (74.2%) not reporting any chronic disease. Among those with chronic disease, hypertension and diabetes were the most common medical conditions (12.1% and 10.5%, respectively).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSinopharm followed by AstraZenca were the most used vaccines among the studied HWs\u0026nbsp;,481\u003cs\u003e\u0026nbsp;\u003c/s\u003e(38.5%) and 391 (31.3%), respectively. The median and IQR between completion of the primary vaccination series and the start of follow-up was 298 days (235\u0026ndash;388), whereas the median time between the booster dose and the start of follow-up was 157 days (IQR: 77\u0026ndash;201). A total of 308 (25.0%) HWs had a history of previous infection, as shown by RT‒PCR positive before/ at enrollment and/or serology positive, representing 164 (18.2%) of those who had completed their primary vaccination series, and 106 (100%) of the unvaccinated participants, with significant differences between groups (P \u0026lt; 0.001).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIV-2 Follow-Up (FU):\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe total follow-up period was 1148.6 person-years, and the average follow-up period was 0.94 years. Participant demographics and clinical characteristics of 1230 participants by vaccination status at the end of follow-up are presented in Table (2), where 19 participants dropped out after enrollment. Participants were followed up biweekly for one year, with 232 (18.9%) HWs developing symptoms and only 108 (46.4%) of them provided NP swabs, Fig (1). Five participants dropped out before contributing as person-time at risk (they were RT‒PCR positive at enrollment but dropped out within 90 days from enrollment. Partial loss to follow up was recorded for 179 participants. All those who were lost to follow up were assessed at their next visit regarding vaccination or symptoms during the missed period. The median duration from receiving the 2nd dose until the end of follow-up was 631 days (IQR: 557\u0026ndash;730 days), while the booster dose to the end of follow-up was 394 days (IQR: 319\u0026ndash;491 days). The cumulative incidence of COVID-19 breakthrough infections was higher among HWs partially vaccinated than among those who were unvaccinated or those who received two or three doses of vaccine (\u003cem\u003ep\u003c/em\u003e =0.025) (Figure 3).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable (1): Participant Demographics and Clinical Characteristics by Vaccination Status at Enrollment\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"707\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVariable\u0026nbsp;\u003c/strong\u003e\u0026copy;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAll Participants\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eUnvaccinated\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePartially Vaccinated *\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFully\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;Vaccinated**\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eBooster Dose\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 59px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eP value\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTotal No. (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e1249 (100%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e107 (8.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e52 (4.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e911 (72.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e179 (14.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAge Group (years)\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e17-30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e315 (25.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e26 (24.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e26 (50.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e226 (24.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e37 (20.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"4\" style=\"width: 59px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e31-40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e329 (26.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e47 (43.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e18 (34.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e227 (24.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e37 (20.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e41-50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e344 (27.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e17 (15.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e5 (9.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e266 (29.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e56 (31.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e\u0026gt; 50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e261 (20.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e17 (15.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e3 (5.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e192 (21.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e49 (27.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMedian (IQR)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e40.0 (30.0-49.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e36.0 (31.0-44.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e30.50 (27.0-37.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e41.0 (31.0-49.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e43.0 (35.0-51.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 59px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSex\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003eMale\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e552 (44.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e44 (41.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e29 (55.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e396 (43.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e83 (46.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 59px;\"\u003e\n \u003cp\u003e0.287\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eFemale\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e697 (55.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e63 (58.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e23 (44.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e515 (56.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e96 (53.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eJob\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 109px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 96px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003ePhysician\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 109px;\"\u003e\n \u003cp\u003e156 (12.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e18 (16.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 108px;\"\u003e\n \u003cp\u003e15 (28.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e101 (11.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 96px;\"\u003e\n \u003cp\u003e22 (12.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"6\" style=\"width: 59px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eNurse\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e536 (42.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e60 (56.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e19 (36.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e370 (40.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e87 (48.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eTechnician\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e73 (5.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e4 (3.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e1 (1.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e61 (6.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e7 (3.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eAdministration\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e270 (21.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e11 (10.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e7 (13.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e224 (24.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e28 (15.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eWorkers\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e196 (15.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e12 (11.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e10 (19.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e143 (15.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e31 (17.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eOthers\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e18 (1.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e2 (1.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e0 (0.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e12 (1.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e4 (2.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eChronic Illness\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 59px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 109px;\"\u003e\n \u003cp\u003e927 (74.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e83 (77.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 108px;\"\u003e\n \u003cp\u003e45 (86.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e670 (73.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 96px;\"\u003e\n \u003cp\u003e129 (72.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 59px;\"\u003e\n \u003cp\u003e0.145\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e322 (25.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e24 (22.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e7 (13.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e241 (26.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e50 (27.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVaccine Brand\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 109px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 96px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eSinovac\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 109px;\"\u003e\n \u003cp\u003e85 (6.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 108px;\"\u003e\n \u003cp\u003e6 (11.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e66 (7.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 96px;\"\u003e\n \u003cp\u003e13 (7.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"7\" style=\"width: 59px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eSinopharm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e481 (38.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e12 (23.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e419 (46.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e50 (27.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eAstraZeneca\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e391 (31.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e26 (50.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e325 (35.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e40 (22.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eModerna\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e22 (1.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e3 (5.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e7 (0.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e12 (6.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eJohnson and Johnson (Janssen)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e12 (1.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e0 (0.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e10 (1.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e2 (1.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003ePfizer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e140 (11.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e5 (9.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e74 (8.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e61 (34.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eHeterologous\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e11(0.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e0 (0.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e10 (1.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e1 (0.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\" style=\"width: 707px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSARS-CoV-2 spike binding antibodies\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNo\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e3 (0.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0 (1 missing)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e3 (0.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 59px;\"\u003e\n \u003cp\u003e0.151\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eYes\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e1245 (99.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e107 (100.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e52 (100.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e908 (99.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e179 (100.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\" style=\"width: 707px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;Evidence of previous infection\u0026nbsp;\u003c/strong\u003eΩ\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e926 (75.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0 (0.0%)\u003c/p\u003e\n \u003cp\u003e(1 missing)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e45 (88.2%)\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e(1 missing)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e735 (81.8%)\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e(12 missing)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e146 (82.0%)\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e(1 missing)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 59px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 131px;\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e308 (25.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e106 (100.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e6 (11.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e164 (18.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e32 (18.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\" style=\"width: 707px;\"\u003e\n \u003cp\u003e\u0026copy; The percentages reported by column\u003c/p\u003e\n \u003cp\u003e*\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ePartially vaccinated\u003cstrong\u003e:\u0026nbsp;\u003c/strong\u003e1 dose of any vaccine (Johnson \u0026amp; Johnson is not included).\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;**Fully Vaccinated: one dose of Johnson \u0026amp; Johnson or 2 doses of any other vaccine.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026euro;\u003c/strong\u003e Chronic Conditions includes Diabetes - heart disease \u0026ndash; Hypertension - Immunodeficiency/organ transplant - lung disease \u0026ndash; Asthma \u0026ndash; Cancer - renal disease - Liver disease - Rheumatological disease\u003c/p\u003e\n \u003cp\u003eΩ Evidence of previous infection mean the presence of either PCR positive before or at enrollment or Serology \u0026nbsp;positive at enrollment\u003c/p\u003e\n \u003cp\u003eSinovac: CoronaVac,\u0026nbsp;Sinopharm:\u0026nbsp;BBIB-CorV or\u0026nbsp;WIBP-CorV, AstraZeneca:\u0026nbsp;ChAdOx1 nCoV-19, Moderna:\u0026nbsp;mRNA-1273,\u003c/p\u003e\n \u003cp\u003eJanssen:\u0026nbsp;Ad26.COV2. S, Pfizer:\u0026nbsp;BNT162b2 mRNA.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable (2): Participant Demographics and Clinical Characteristics by Vaccination Status at the Start of Follow-Up\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"696\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVariable\u003c/strong\u003e\u0026copy;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAll Participants*\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eUnvaccinated (any vaccine)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePartially vaccinated**\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFully\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;Vaccinated***\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eBooster dose\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eP value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u003cstrong\u003en= 1230\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u003cstrong\u003en= 103 (8.4%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e\u003cstrong\u003en= 52 (4.2%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e\u003cstrong\u003en= 900 (73.2%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u003cstrong\u003en= 175 (14.2%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003eAge Group (Years)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 103px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e17-30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e309 (25.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e25 (24.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 103px;\"\u003e\n \u003cp\u003e26 (50.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 108px;\"\u003e\n \u003cp\u003e222 (24.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e36 (20.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"4\" valign=\"top\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003e31-40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e326 (26.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e45 (43.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 103px;\"\u003e\n \u003cp\u003e18 (34.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 108px;\"\u003e\n \u003cp\u003e226 (25.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e37 (21.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003e41-50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e337 (27.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e17 (16.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 103px;\"\u003e\n \u003cp\u003e5 (9.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 108px;\"\u003e\n \u003cp\u003e263 (29.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e52 (29.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003e\u0026gt; 50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e258 (21.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e16(5.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 103px;\"\u003e\n \u003cp\u003e3 (5.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 108px;\"\u003e\n \u003cp\u003e189 (21.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e50 (28.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMedian IQR\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e40.0 (30.0-49.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e36.0 (31.0-44.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e30.5 (27.0-37.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e41.0 (31.0-49.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e43.0 (34.5-51.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSex\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003eMales\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e545 (44.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e44 (42.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e29 (55.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e390 (43.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e82 (46.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" valign=\"top\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e0.298\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003eFemales\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e685 (55.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e59 (57.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 103px;\"\u003e\n \u003cp\u003e23 (44.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 108px;\"\u003e\n \u003cp\u003e510 (56.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e93 (55.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eChronic illness\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 103px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e914 (74.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e80 (77.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 103px;\"\u003e\n \u003cp\u003e45 (86.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 108px;\"\u003e\n \u003cp\u003e662 (73.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e127 (72.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" valign=\"top\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e0.156\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e316 (25.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e23 (22.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e7 (13.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e238 (26.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e48 (27.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;Vaccine Brand\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 103px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003eSinovac\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e85 (6.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e0 (0.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 103px;\"\u003e\n \u003cp\u003e6 (11.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 108px;\"\u003e\n \u003cp\u003e66 (7.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\" style=\"width: 102px;\"\u003e\n \u003cp\u003e13 (7.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"8\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003eSinopharm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e474 (38.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0 (0.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e12 (23.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e414 (46.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e48 (27.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003eAstraZeneca\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e388 (31.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0 (0.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e26 (50.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e322 (35.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e40 (22.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003eSputnik\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e1 (0.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e0 (0.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e0 (0.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e1 (0.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003eModerna\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e22 (1.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0 (0.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e3 (5.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e7 (0.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e12 (6.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003eJohnson and Johnson (Janssen)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e11 (0.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0 (0.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e0 (0.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e10 (1.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e1 (0.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003ePfizer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e136 (11.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0 (0.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e5 (9.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e71 (7.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e60 (34.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\" style=\"width: 114px;\"\u003e\n \u003cp\u003eHeterologous\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e10 (0.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0 (0.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 103px;\"\u003e\n \u003cp\u003e0 (0.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e10 (1.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e0 (0.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"7\" valign=\"bottom\" style=\"width: 696px;\"\u003e\n \u003cp\u003e\u0026copy; The percentages reported by column\u003c/p\u003e\n \u003cp\u003e* There are 19 missing\u0026nbsp;participants (14 participants were dropped out just after enrollment (death, retiring, or change of workplace)\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eand 5 dropped out before contribution as person-time at risk (PCR positive at enrollment). \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e**\u003cstrong\u003e\u0026nbsp;Partially vaccinated:\u0026nbsp;\u003c/strong\u003e1 dose any vaccine (Johnson \u0026amp; Johnson is not included)\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;***\u003cstrong\u003eFully\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eVaccinated:\u0026nbsp;\u003c/strong\u003e2 doses\u0026nbsp;any vaccine, except for\u0026nbsp;Johnson \u0026amp; Johnson (Janssen) only one dose considered fully vaccinated\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026euro;\u003c/strong\u003e Chronic Conditions includes\u0026nbsp;Diabetes - Heart disease \u0026ndash; Hypertension - Immunodeficiency/organ transplant - Lung disease \u0026ndash; Asthma \u0026ndash; Cancer - Renal disease - Liver disease - Rheumatological disease\u003c/p\u003e\n \u003cp\u003eSinovac: CoronaVac,\u0026nbsp;Sinopharm:\u0026nbsp;BBIB-CorV or\u0026nbsp;WIBP-CorV, AstraZeneca:\u0026nbsp;ChAdOx1 nCoV-19, Moderna:\u0026nbsp;mRNA-1273,\u003c/p\u003e\n \u003cp\u003eJanssen:\u0026nbsp;Ad26.COV2.S, Pfizer:\u0026nbsp;BNT162b2 mRNA, Sputnik: Gam-COVID-Vac.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIV-3 Laboratory results:\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAt enrollment, SARS-CoV-2 spike-binding antibodies were detected in 1245/1248 (99.8%) of the recruited participants (figure (1) and table (1)). The level was \u0026gt;2500 U/ml in 664/1245 (53.3%) of the recruited HWs, and three samples were negative for SARS-CoV-2 spike-binding antibodies, all of which were from HWs who had completed their primary vaccination series. All unvaccinated HWs (106, 100%) were seropositive. At enrollment, SARS-CoV-2 RNA positivity was detected among 119/1235 (9.5%) HWs. Among the 148 symptomatic HWs, only 13 (8.8%) were SARS-CoV-2 RNA positive, while most SARS-CoV-2 RNA-positive HWs were asymptomatic (106/119\u0026ndash;89%). Neither hospitalizations nor deaths were recorded among the recruited participants, table (3). During biweekly follow-up visits within a one-year period, 232 HWs developed symptoms compatible with the COVID-19 case definition, 108 (46.4%) of whom provided nasopharyngeal samples. Among these samples, 18 (16.6%) were SARS-CoV-2 RNA positive, and the peak infection rate was recorded in March 2023. The symptomatic RT‒PCR-confirmed COVID-19 infection, which corresponded to an incidence of 0.44 cases per 10,000 person-days. There were 10(1.1) cases among the fully vaccinated participants, 3(5.8%) among the partially vaccinated participants, 2(1.1) among those who had received a booster dose, and 3(2.9%) among unvaccinated participants (Table 3).\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable (3)\u003cspan dir=\"RTL\"\u003e\u0026nbsp;\u003c/span\u003eDescription of the Clinical Endpoints of COVID-19 RNA-Positive Participants\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"690\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTotal Cohort\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"5\" style=\"width: 534px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eVaccination Status at the Time of Onset\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAt Enrollment\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTotal\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003en (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eUnvaccinated\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003en (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePartially vaccinated*\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003en (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFully\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eVaccinated**\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003en (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eBooster\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003en (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003eTotal cohort with PCR swab results\u003c/p\u003e\n \u003cp\u003e(14 excluded)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e1235\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003e107\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e899\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e178\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003eAll positive PCR\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e119/1235 (9.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003e12/107 (11.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e4/51 (7.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e79/899 (8.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e24/178 (13.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003eSymptomatic HWs with positive PCR\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e13/148 (8.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003e1/12 (8.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e1/5 (20%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e8/110 (7.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e3/21 (14.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003eAsymptomatic HWs with positive PCR\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e106/1087 (9.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003e11/95 (11.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e3/46 (6.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e71/789 (9.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e21/157 (13.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003eSymptomatic cases with positive PCR required medical care\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e8/13 (61.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003e1/1 (100%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e4/8 (50%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e3/3 (100%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003eSymptomatic cases with positive PCR required hospitalization\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003eSymptomatic cases with positive PCR died\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\" style=\"width: 690px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAt End of the Follow Up (Total Cohort 1230 as 19 dropped out before being at risk)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003eTotal Followed Up Participants\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e1230\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003e103\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e900\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e175\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003eSymptomatic HWs with Positive PCR\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e18/1230 (1.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003e3/103(2.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e3/52 (5.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e10/900 (1.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e2/175 (1.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003eSymptomatic HWs with Positive PCR (18) Requiring Medical Care\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e12 (66.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e3 (100%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e7 (70.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e2 (100%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003eSymptomatic with Positive PCR Requiring Hospitalization\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 156px;\"\u003e\n \u003cp\u003eSymptomatic HWs with Positive PCR died\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 107px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 91px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 114px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e*\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ePartially vaccinated\u003cstrong\u003e:\u0026nbsp;\u003c/strong\u003e1 dose of any vaccine except for Johnson and Johnson.\u003c/p\u003e\n\u003cp\u003e**Fully Vaccinated: one dose of Johnson and Johnson or 2 doses of any other vaccines.\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIV-4 Vaccine effectiveness\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIV-4-1 Vaccine effectiveness per number of doses:\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFull vaccination or booster dose VE against symptomatic PCR-confirmed COVID-19 was not significantly different compared with unvaccinated HWs, with adjusted VE values of 68% (95%CI -28% to 92%) and 64% (95%CI -170% to 95%), respectively, P =0.106 and 0.318 respectively, table (4-A) and figures (4-5).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIV.4.2\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;Vaccine effectiveness per type of vaccine:\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThirteen symptomatic HWs had RT‒PCR-confirmed SARS‒CoV-2 infection, three of them being unvaccinated. One, five, and four HWs with RT-PCR confirmed COVID-19 infection were vaccinated with Sinovac, Sinopharm and AstraZeneca, respectively, with adjusted VE% of 65% (95%CI -59% to 92%) and 85% (95%CI: -19% to 98%) for Sinopharm and AstraZeneca, respectively compared to unvaccinated group, P =0.176, and P=0.073 respectively. For Sinovac, as there was only one symptomatic case, so VE could not be calculated, table (4-A) and figures (4-5). \u003cstrong\u003eBecause of the limited number of events, VE was not fully calculated; however, those who had received Pfizer, Moderna, or Johnson and Johnson (Janssen) did not show any breakthrough infections.\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIV\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e.4\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e.3 Vaccine effectiveness by prior infection:\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAmong participants with prior infection (total 263), the\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ecombined effect of previous infection and vaccination had an adjusted VE of 89% (95% CI: -33% to 99%), with no significant difference detected for unadjusted/adjusted VE among fully vaccination compared to the unvaccinated, P=0.163 and P=0.082 respectively, table (4-B), figures (4-5). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIV\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e.4\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e.4\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003eVaccine effectiveness by time since vaccination:\u003c/em\u003e\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAmong two-dose vaccinated participants, 10/900 developed breakthrough infection, all of whom were detected among those with a duration \u0026gt;365 days from the 2nd dose with an adjusted VE of 68% (95%CI: -25% to 92%) compared with unvaccinated participants, P = 0.113, table (4-C) and figures (4-5). Unadjusted and adjusted VE among participants who had received a booster dose compared with those who had received 2 vaccine doses were not significantly different (P = 0.0875, figure (4-5).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBecause of limited events, the VE in HWs receiving booster doses against RT‒PCR confirmed that COVID‒19 infection stratified by previous infection status and vaccine type could not be evaluated.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIV\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e.4\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e.5 Sensitivity analysis of vaccine effectiveness\u003c/em\u003e\u003c/strong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe sensitivity analysis revealed nearly similar results for VE after the exclusion of participants with a decrease in the post-infection period at risk for 60 days instead of 90 days, with unadjusted VE values of 65% (95%CI: -27% to 90%), and adjusted VE 68% (95%CL: -29% to 92%), with P value for both =0.111. The unadjusted VE after excluding symptomatic patients who refused to provide nasopharyngeal swabs was 67% (95%CI: -19% to 91%), and the\u003cem\u003e\u0026nbsp;\u003c/em\u003eadjusted VE was 69% (95%CL -24% to 92%) with P value for both =0.116. When HWs who had a duration of less than 21 days between receiving the first and second doses of the vaccine were excluded, the unadjusted VE was 64% (95%CI -30% to 90%) and the adjusted VE 67% (95%CL -33% to 92%), with P value for both =0.121, figures (6-7).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable (4): A- Vaccine Effectiveness against Symptomatic PCR Confirmed SARS-CoV-2 Infection according to number of vaccine doses and Vaccine Type\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"744\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eTwo Doses\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(All Vaccines) *\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;N\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTotal Person-Time (Days)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 90px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSymptomatic COVID-19 PCR-Confirmed Infections\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eIncidence /10,000 person-days\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eUnadjusted\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eVE\u0026nbsp;\u003c/strong\u003e(\u003cstrong\u003e95% CI)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eP\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eValue\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAdjusted VE\u003c/strong\u003e \u003cstrong\u003e(95% CI)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 72px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eP\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eValue\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003eTotal cohort\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 56px;\"\u003e\n \u003cp\u003e1230\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e406382\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 90px;\"\u003e\n \u003cp\u003e18*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e0.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 96px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 48px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003eUnvaccinated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 56px;\"\u003e\n \u003cp\u003e103\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e29604\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 90px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e1.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003eReference\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 96px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 48px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u0026ge;14days from 2nd dose\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 56px;\"\u003e\n \u003cp\u003e900\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e305164\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 90px;\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e0.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e65% (-26% - 90%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e0.107\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 96px;\"\u003e\n \u003cp\u003e68% (-28% - 92%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 48px;\"\u003e\n \u003cp\u003e0.106\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u0026ge;14days from Booster dose\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 56px;\"\u003e\n \u003cp\u003e175\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e54035\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 90px;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e0.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e60% (-143% - 93%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e0.323\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 96px;\"\u003e\n \u003cp\u003e64% (-170% - 95%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 48px;\"\u003e\n \u003cp\u003e0.318\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"13\" style=\"width: 720px;\"\u003e\n \u003cp\u003eBy Brand\u0026nbsp;of Vaccine\u0026nbsp;for Total Cohort\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003eTotal cohort*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 56px;\"\u003e\n \u003cp\u003e1003\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e334768\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 90px;\"\u003e\n \u003cp\u003e13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e0.39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 48px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003eUnvaccinated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 56px;\"\u003e\n \u003cp\u003e103\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e29604\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 90px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e1.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003eReference\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 48px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003eSINOVAC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 56px;\"\u003e\n \u003cp\u003e66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e22343\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 90px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e0.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"5\" style=\"width: 306px;\"\u003e\n \u003cp\u003eISD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003eSINOPHARM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 56px;\"\u003e\n \u003cp\u003e414\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e138825\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 90px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e0.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e60% (-66% - 91%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e0.205\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 96px;\"\u003e\n \u003cp\u003e65% (-59% - 92%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 48px;\"\u003e\n \u003cp\u003e0.176\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003eAstraZeneca\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 56px;\"\u003e\n \u003cp\u003e322\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e110324\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 90px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e0.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e63% (-67% - 92%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e0.196\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 96px;\"\u003e\n \u003cp\u003e85% (-19% - 98%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 48px;\"\u003e\n \u003cp\u003e0.073\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"13\" style=\"width: 720px;\"\u003e\n \u003cp\u003eTotal cohort of the unvaccinated were 103 and fully vaccinated were 900\u003c/p\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; CI: confidence Interval \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; VE: Vaccine Effectiveness \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; ISD: insufficient data to calculate VE\u003c/p\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; *Three symptomatic COVID-19 PCR-confirmed infections were detected among partially vaccinated group and were excluded from the analysis of VE\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eSinovac: CoronaVac, Sinopharm: BBIB-CorV or WIBP-CorV, AstraZeneca: ChAdOx1 nCoV-19.\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"13\" valign=\"top\" style=\"width: 720px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTable (4): B- Combined Effect of Previous Infection + Vaccination on VE against SARS-CoV-2 Infection (Hybrid Immunity)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 108px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eTwo Doses\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(All Vaccines)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;N\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTotal Person-Time (Days)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 90px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSymptomatic COVID-19 PCR-Confirmed Infections\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003eIncidence\u003cstrong\u003e\u0026nbsp;/10,000 person-days\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eUnadjusted\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eVE\u0026nbsp;\u003c/strong\u003e(\u003cstrong\u003e95% CI)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eP Value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAdjusted VE\u003c/strong\u003e \u003cstrong\u003e(95% CI)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 48px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eP Value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003eTotal Cohort\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 56px;\"\u003e\n \u003cp\u003e263\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e78825\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 90px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e0.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 48px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003eUnvaccinated with past infection\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 56px;\"\u003e\n \u003cp\u003e102\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e29268\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 90px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e1.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003eReference -\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 48px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 108px;\"\u003e\n \u003cp\u003e\u0026ge;14Days from 2nd Dose among fully vaccinated with past infection\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 56px;\"\u003e\n \u003cp\u003e161\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e49909\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 90px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e0.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e80% (-92% - 98%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e0.163\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 96px;\"\u003e\n \u003cp\u003e89% (-33% - 99%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 48px;\"\u003e\n \u003cp\u003e0.082\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"13\" valign=\"top\" style=\"width: 720px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eTable (4): C-Two doses Vaccine Effectiveness Against Symptomatic COVID-19 Infection, Incorporating Time Since Vaccination\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eTwo Doses\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(All Vaccines)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 44px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;N\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 82px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTotal person-time (days)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003eSymptom. COVID-19 PCR-Confirmed Infections\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 86px;\"\u003e\n \u003cp\u003eIncidence\u003cstrong\u003e\u0026nbsp;/10,000 person-days\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eUnadjusted\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eVE\u0026nbsp;\u003c/strong\u003e(\u003cstrong\u003e95% CI)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eP Value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 93px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAdjusted VE\u003c/strong\u003e \u003cstrong\u003e(95% CI)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 51px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eP Value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003eTotal Cohort\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 44px;\"\u003e\n \u003cp\u003e1003\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 82px;\"\u003e\n \u003cp\u003e331068\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003e13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 86px;\"\u003e\n \u003cp\u003e0.39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 93px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 51px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003eUnvaccinated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 44px;\"\u003e\n \u003cp\u003e103\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 82px;\"\u003e\n \u003cp\u003e29604\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 86px;\"\u003e\n \u003cp\u003e1.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003eReference\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e\u0026nbsp;-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 93px;\"\u003e\n \u003cp\u003e\u0026nbsp;-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 51px;\"\u003e\n \u003cp\u003e\u0026nbsp;-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e14days-\u0026le;365Days from 2nd dose\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 44px;\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 82px;\"\u003e\n \u003cp\u003e486\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 86px;\"\u003e\n \u003cp\u003e0.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"5\" style=\"width: 306px;\"\u003e\n \u003cp\u003eISD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 120px;\"\u003e\n \u003cp\u003e\u0026gt;365Days from 2nd dose\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 44px;\"\u003e\n \u003cp\u003e893\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 82px;\"\u003e\n \u003cp\u003e300978\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 82px;\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 86px;\"\u003e\n \u003cp\u003e0.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 102px;\"\u003e\n \u003cp\u003e64% (-27% - 90%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e0.113\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 93px;\"\u003e\n \u003cp\u003e68% (-25% - 92%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 51px;\"\u003e\n \u003cp\u003e0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"13\" valign=\"top\" style=\"width: 720px;\"\u003e\n \u003cp\u003e\u0026nbsp;CI: confidence Interval\u003c/p\u003e\n \u003cp\u003eVE: Vaccine Effectiveness-\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eISD: insufficient data to calculate VE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 24px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eRecognizing the critical importance of leveraging local data to inform national and regional vaccine policies, the WHO-EMRO) provided technical and financial support to four regional countries to conduct SARS-CoV-2 vaccine effectiveness studies(18). Healthcare workers (HWs) faced a significant risk of exposure to SARS-CoV-2 infection, as well as increased morbidity and mortality, while also being at a high risk of transmitting the virus to hospitalized patients, who are often more vulnerable to severe COVID-19 outcomes (25).Thus, the current study was conducted to measure SARS-CoV-2 VE against symptomatic RT‒PCR-confirmed SARS‒CoV-2 infection among HWs eligible for vaccination at Al-Azhar University hospitals. A total of 1249 out of 13260 HWs were recruited from the workforce in the five hospitals distributed among three main governorates in Egypt. Enrollment\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ewas conducted between July and August 2022, when almost all HWs were vaccinated with primary vaccination series or by a booster (87.3%), and different types of COVID-19 vaccines were available. Only one participant received the booster dose during the follow-up period. For the overall cohort, vaccinated participants had received their second dose long before enrollment (median of 294.0 days (IQR: 232--387)). Different vaccine brands were introduced in Egypt, and most of them were provided to the studied participants within the study cohort, with high vaccination coverage of 1142/1249 (91.4%). Several online surveys have been conducted in Egypt to study COVID-19 vaccination coverage and population perceptions, and different acceptance rates have been reported among the Egyptian population, ranging from 31.1% to 71.1%(3,14,15,26). An earlier questionnaire-based cross-sectional Egyptian study conducted in 2021 reported 21% vaccine coverage among HWs (27), which increased to 70.5% in a more recent similar study (28).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo study VE, unvaccinated participants were used as a reference group. VE against symptomatic RNA-confirmed cases was estimated via Cox proportional hazards regressions adjusted for age, sex, and comorbidities. To avoid bias due to insufficient data for some vaccines or subgroups, VE estimates were not calculated when the total number of HWs with COVID-19 was less than five. In addition, because of the small number of events, VE estimates were often inconclusive after adjustment, likely due to the reduced statistical power. The limited number of events also resulted in significant variability in the outcomes, as evidenced by the broad confidence intervals observed for the VE estimates (25) . According to the FDA-issued guidance, the COVID-19 vaccine efficacy rate should be at least 50% to be considered successful, although the lower bound of the confidence interval can be as low as 30% (29). In the current study, the adjusted VE among the whole study cohort was 68% (95% CI -28% to 92%) for those who completed their primary vaccination series. \u0026nbsp;\u003cstrong\u003eSimilarly, the adjusted VE for participants who completed their primary vaccination series 68% (95% CI -28% to 92%) and those who received a booster dose 64% (95% CI -170% to 95%) showed no significant difference (P\u0026gt;0.05).\u0026nbsp;\u003c/strong\u003eThis is in line with previous studies (30). However, it\u0026nbsp;was previously shown that the booster dose remained effective for four months following vaccination and then declined substantially thereafter (30\u0026ndash;32)\u0026nbsp;Inconclusive results with wide confidence intervals were also reported in three other VE studies conducted in three different countries within the region, and this was explained by the increasing challenge of obtaining reliable VE estimates late during the COVID-19 pandemic in the Omicron dominant period.\u003c/p\u003e\n\u003cp\u003eReal-time RT‒PCR has been employed worldwide to detect SARS-CoV-2 due to the minimal likelihood of false positive results (33); however, negative real-time RT‒PCR results do not exclude possible infection. Clerici et al (2021) reported that in 233 patients, the sensitivity of RT‒PCR for the detection of COVID‒19 RNA from NP swabs was 77% (95% CI, 73--81%) (34). Although the analytical performance of RT‒PCR is well accepted, pre-analytical factors cannot be excluded. At enrollment, SARS-CoV-2 RNA was detected among 119/1230 (9.6%) HWs; of those HWs, only 13 (10.9%) were symptomatic. These findings indicate that most COVID-19-positive patients are asymptomatic. However, neither hospitalization nor death was recorded among the recruited participants. This can likely be explained by occurring during the Omicron era, where the Omicron variant and its subvariants had mainly driven infections worldwide, as reported by the WHO (8). It accounted for more than 98% of the publicly available sequences since February 2022 and constituted the genetic background from which new SARS-CoV-2 variants are likely to emerge (35) It is notable that all unvaccinated HWs (107,100%) were seropositive, and 83 (77.6%) did not have RT‒PCR results indicating COVID-19+ infection at enrollment or before enrollment, indicating the presence of asymptomatic infection. According to the CDC, some respiratory viruses, mainly influenza and RSV, share very similar symptoms with COVID-19, which may also explain the negative RNA results for COVID-19 despite symptoms (36). A total of 232 participants developed COVID-19 symptoms during follow up, and only 108 (46.4%) provided a nasopharyngeal sample, of whom 18/108 (16.7%) individuals were SARS-CoV-2 RNA positive, with an incidence of 0.44 cases per 10000 person-days. Among these 18 positive cases, 15/18 (83.3) were vaccinated. A total of 12/18 (66.7%) HWs required medical treatment, but neither hospitalization nor death was recorded among HWs. This was in accordance with the WHO which stated that people can still develop COVID-19 after vaccination but are more likely to have mild or no symptoms (8). Moreover, enrollment of participants occurred during the fifth wave of the COVID-19 pandemic (July and August 2022), which showed a high prevalence of Omicron variants. Compared with the early variants, Omicron variant is associated with a greater rate of transmission, a lower hospitalization rate and case fatality rate (4). A recent Egyptian study revealed that symptoms were reported less often in the omicron cohort than in patients with other variants (15).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eImportantly, at enrollment, a total of 1245/1248 (99.8%) of the studied participants were seropositive for COVID-19 anti-spike-binding antibodies with levels \u0026gt; 2500 U/ml in 664/1245 (53.3%) of participants. Notably, \u003cstrong\u003eonly three participants (0.3%) had negative binding antibodies despite completing the vaccine doses\u003c/strong\u003e\u003cstrong\u003e.\u003c/strong\u003e Moreover, all unvaccinated participants (107) were seropositive, indicating that they had previously contracted COVID-19 infection. Anti-S and overall SARS-CoV-2-specific IgG remain detectable in approximately 90% of persons who seroconvert up to 10 months to one-year post-infection (37,38). Previous studies have revealed that antibody titers peak within 3\u0026ndash;5 weeks following infection and then begin to wane in a manner that varies by individual, target antigen, antibody isotype, and assay used (37,39). A growing body of evidence confirms that the COVID-19 vaccine is important for preventing severe infection, hospitalization and mortality. This is in accordance with the current study, where most HWs were vaccinated and none of the HWs who experienced breakthrough infection needed hospitalization or died. Additionally, the CDC has confirmed that higher antibody titters are associated with a decreased risk of subsequent symptomatic SARS-CoV-2 infection (40).\u003c/p\u003e\n\u003cp\u003eWhen the binding antibody titers\u0026nbsp;were evaluated in breakthrough infection, with SARS-CoV-2 after two or more doses of the vaccine, it was shown that those with breakthrough infection already had antibody titers of tens of thousands of U/mL. This can be related to \u0026ldquo;hybrid immunity\u0026rdquo; after spontaneous infection following two or more doses of the vaccine (4).\u0026nbsp;Most people with COVID-19 infection develop detectable anti-SARS-CoV-2 antibodies, with\u003cs\u003e\u0026nbsp;\u003c/s\u003eseroconversion rates of 90% or higher (41,42). CDC reported that the immunity provided by vaccines and prior infection is high but incomplete (40). Post-infection antibodies target the spike (S) protein, receptor binding domain (RBD) of the spike protein and nucleocapsid (N) core protein; meanwhile, vaccination induces the production of (S) and anti-RBD binding and neutralizing antibodies in the blood but not anti-N antibodies (40).If breakthrough infections are frequent, severe, or highly transmissible, there may be a need for additional vaccine doses, adjustments to vaccine formulations, or non-pharmaceutical interventions (or a combination of these strategies) to decrease the rate of infection(X8).\u003c/p\u003e\n\u003cp\u003eWhen the full cohort was stratified by previous infection status for full dose(s) vaccinated participants who had RT‒PCR- SARS-CoV-2 confirmed infection prior to or at enrollment (hybrid immunity), the adjusted two-dose VE \u003cem\u003evs\u003c/em\u003e the unvaccinated\u0026nbsp;increased to\u0026nbsp;89% CI (-33%-99%) (P\u0026gt;0.05).\u0026nbsp;Notably, the cumulative incidence of COVID-19 breakthrough infections was significantly higher among those who were partially vaccinated compared to those who were unvaccinated or those who received two or three doses of the vaccine (\u003cem\u003ep\u003c/em\u003e \u0026lt;0.05). This may be due to natural immunity, where all unvaccinated HWs reported previous\u0026nbsp;\u003cbr\u003e\u0026nbsp;SARS-CoV-2 infection either before or at enrollment, as detected by RT‒PCR, whereas the rates of previous SARS-CoV-2 infection among HWs with partial vaccination, those who received a full primary series or a booster dose were 11.8%, 18.2% and 18%, respectively.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePrevious studies have shown that the immune response following infection continues to provide at least 50% protection against reinfection for 1\u0026ndash;2 years following initial infection with SARS-CoV-2 (43,44). Additionally, in a study among HWs vaccinated 7\u0026ndash;11 months after infection with COVID-19, the antibody titers measured 6 days after their first dose were twice as high as the antibody titers measured one month after their initial infection. Moreover, they were able to neutralize different COVID-19 variants, irrespective of vaccine type, number of doses, or pre-vaccination antibody titers (45). A recent systematic review on measuring the magnitude and duration of hybrid immunity against severe disease and infection caused by the Omicron variant revealed that individuals with hybrid immunity had greater magnitude and durability of protection than individuals who had no history of previous infection (46). It is worth noting that prior SARS-CoV-2 infection lowered the risk of re-infection, even without vaccination. The current findings, which show the protective effect of infection alone during the pre-Omicron period, have also been observed in other studies(25).\u003c/p\u003e\n\u003cp\u003eIn the studied cohort, only seven HWs were 14\u0026ndash;365 days from the 2nd dose; none of them developed COVID-19 symptoms during follow-up, whereas all other HWs were \u0026gt;365 days from their completion of the primary vaccination series. The adjusted VE was 68% (CI -25%-92%) among HWs vaccinated \u003cem\u003evs\u003c/em\u003e the\u003cem\u003e\u0026nbsp;\u003c/em\u003eunvaccinated, P \u0026gt; 0.05. A recent study indicated rapid waning of the booster dose with increased time from vaccination (47). A model linking immunity levels and protection to VE data from England for three vaccines (Oxford/AstraZenecaAZD1222, Pfizer-BioNTech BNT162b2, Moderna mRNA-1273) and two variants (Delta, Omicron) projected gradual waning to moderate protection after 1 year(48). The current study could not show a significant effect of a booster dose.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA recent European study showed that VE waned 12 weeks after vaccine administration and decreased even further after 24 weeks (30). It has also been shown that the time since the last booster dose is more important than the total number of doses administered for protection against severe COVID-19 (49). On the other hand, when VE is evaluated in relation to the vaccine brand, limited infection events did not allow VE estimation among HWs in the study cohort. However, there was no significant difference between each vaccine type \u003cem\u003eand the\u003c/em\u003e unvaccinated group (P \u0026gt; 0.05). The VE of all the vaccines decreased over time, implying that, to reach herd immunity, booster shots are needed. VE was higher in mRNA vaccines than in the other vaccines, as no breakthrough infection was recorded among HWs receiving the Pfizer or Moderna vaccines, whereas the adjusted VE for AstraZeneca was 85%, 95% CI (-19% - 98%), and that of Sinopharm was 65%, 95% CI (-59% - 92%), indicating a lower VE for inactivated vaccines than for the mRNA vaccines; however, because there were few or no events, VE for Sinovac could not be calculated. This finding is in line with other studies (50). Of note, the relative VE of the 3rd dose against RT‒PCR-confirmed COVID‒19 infection, stratified by previous infection status and vaccine type, could not be calculated due to insufficient data and limited events. Sensitivity analysis revealed similar results, with the exclusion of participants who had durations \u0026lt; 21 days, durations between the 1\u003csup\u003est\u003c/sup\u003e and 2\u003csup\u003end\u003c/sup\u003e doses, or symptomatic patients who refused to have their nasopharyngeal swabs taken or whose disease duration decreased to 60 days instead of 90 days.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWith respect to the 8% of unvaccinated HWs, it is well known that despite worldwide measures to ensure that COVID-19 vaccine use was affordable, accessible, and beneficial to the community, vaccine hesitancy among Egyptians was / is an issue of concern (15). COVID-19 vaccine refusal was multifactorial in these studies and was attributed mainly to doubts about vaccine effectiveness, a lack of trust due to rapid vaccine production, inadequate information, and a fear of vaccine side effects. As emphasized by Kandeel et al. (2023), Egypt being a low- and middle-income countries (LMIC), still faces considerable obstacles in receiving, distributing, and accepting vaccinations at the community level (4).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLimitations:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSome limitations\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ewere encountered, such as starting the study in the pandemic declining phase, during which too few infections occurred and that may have affected VE estimates. \u003cstrong\u003eLow-event VE estimates emphasize the importance of sample size, and the small number of cases often yielded inconclusive results.\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u0026nbsp;\u003c/strong\u003eOnly 109/232 nasopharyngeal swab samples were available from the follow up for evaluation. Excluding follow up of asymptomatic participants, who presented the main COVID-19 infection status at that time of Omicron dominance, is also a limitation that must be considered. The use of up to six vaccine brands, together with a small sample size, provided insufficient data that did not allow calculation of vaccine-specific VEs. The lack of viral genetic sequence data for the study of circulating virus variants and the lack of detection of anti-N antibodies to differentiate between immunity due to vaccination only or \u003cstrong\u003einfection-induced immunity\u003c/strong\u003e are issues of concern.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThis is the first HW cohort multicenter study conducted in Egypt to estimate VE among HWs. While the overall VEs demonstrated protection against symptomatic disease, the few events reported during follow-up limit the study\u0026rsquo;s statistical power, and most estimates were inconclusive. However, the point estimates and crude VE estimates may support the importance of completing the primary vaccination series against COVID-19. This study\u0026rsquo;s\u003cs\u003e\u0026nbsp;\u003c/s\u003eresults could provide a platform for conducting and evaluating COVID-19 VE studies in the future that will help decision makers in devising / formulating vaccine policies at the national and regional levels and better understand the disease burden and effects of adopted vaccination policies. It could also provide evidence on implementation challenges and feasibility, underscoring how future immunization agenda must be driven. Many inquiries still need answers, such as the optimal number of booster doses, duration of protection, and vaccine adverse events. The study of COVID-19 variants is still essential for evaluating vaccine effectiveness, as mutations in the spike protein of variant(s) of interest could impair the binding ability of the antibodies.\u003c/p\u003e"},{"header":"DECLARATIONS","content":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eEthics approval and consent to participate:\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of Al-Azhar University on 5/12/2021 (AU-REC-2021-0002). Informed written consent was provided by each participant.\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eClinical trial\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;number\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e:\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eConsent for publication:\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo individual person\u0026rsquo;s data in any form is included, where\u0026nbsp;each participant was allocated a unique study ID number- using a barcode-at enrollment. Informed written consent was provided by each participant.\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAvailability of data and material\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data presented in the manuscript is shared with WHO regional office. Requests to access any datasets or codes/scripts used for data analysis should be directed to the corresponding author, whenever reasonable.\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eCompeting interests\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo competing or conflicting interest are declared.\u003c/p\u003e\n\u003cp\u003eThis study received full technical and financial support from the WHO Regional Office for the Eastern Mediterranean. WHO registries file number: 2022/1276447-\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFunding:\u003c/em\u003e\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis research received funding/financial support from the World Health Organization (WHO) for the duration of the study (September 2021\u0026ndash;April 2024). WHO Regional Office for Eastern Mediterranean Region (EMRO)\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAuthors\u0026apos; contributions:\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;SZN and SII are the PI and Co PI of the project, both responsible for designing research idea and developing the research question and rationale, conceptualization and methodology. They conducted literature review, results interpretation and manuscript editing. KZ, KM, FK and RA are the WHO partners, who shared in conceptualization, methodology, validation, supervised the project implementation and provided technical support. They also critically revised the final manuscript draft. ZS, EAA, ESS, EF, and EAK are the leaders of the five University hospitals\u0026rsquo; team, who were responsible for HWs recruitment and monitoring their follow up. Sumaya H. ESH, EE, ENA, EA, AN, MS, AAA, AEA, KAS, SMA, EAM, BIM, HMM, GAM, AWO, EAW, HMA, Amro M. HAM, AE, MAQ, AOM, SSS were responsible for HWs\u0026rsquo; sampling, data collection and follow up. RA, GA, KA, and EAM are responsible for conducting molecular techniques for detection of SARS COV-2 RNA, communication with the hospitals\u0026rsquo; team, preparing participants \u0026rsquo;files\u0026rsquo; for NRC team and manuscript draft writing. MS, AA, ABW, SMA and BIM are engaged in SARS-CoV-2 antibody detection. SSI, EGA, ADE, HHM, ESE, SR and ED were responsible for data entry, data management and statistical analysis.SM, as the University vice president supervised the project implementation and facilitated any administration constrains. All the authors have seen and agreed to the submission of the manuscript and their inclusion of name(s) as co-author(s).\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAcknowledgements\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;Thanks,\u003c/strong\u003e and appreciation to the WHO Regional Office for Eastern Mediterranean and the WHO country office in Egypt\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003efor the resources provided that enabled the successful execution of this project. We acknowledge the WHO knowledge and expertise that contributed significantly to the project\u0026rsquo;s success. The extraordinary contributions of the WHO and continuous support greatly improved the quality of this study. The authors are also grateful to Giulio Borghi, Manuela Runge, and Carsten Mantel, MMGH Consulting, Zurich, Switzerland, for helpful input during the initial analysis and presentation of the results.\u003c/p\u003e"},{"header":"REFERENCES","content":"\u003col\u003e\n\u003cli\u003eEgypt COVID - Coronavirus Statistics - Worldometer [Internet]. [cited 2024 Aug 19]. Available from: https://www.worldometers.info/coronavirus/country/egypt/\u003c/li\u003e\n\u003cli\u003eBeginning of the end of coronavirus? - Egypt - Al-Ahram Weekly - Ahram Online [Internet]. [cited 2024 Aug 19]. 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Available from: https://www.who.int/publications/i/item/WHO-2019-nCoV-Surveillance_Case_Definition-2022.1\u003c/li\u003e\n\u003cli\u003eLipsitch M, Krammer F, Regev-Yochay G, Lustig Y, Balicer RD. SARS-CoV-2 breakthrough infections in vaccinated individuals: measurement, causes and impact. Nature Reviews Immunology 2021 22:1 [Internet]. 2021;22(1):57\u0026ndash;65. Available from: https://www.nature.com/articles/s41577-021-00662-4\u003c/li\u003e\n\u003cli\u003eKheirandish M, Karimian Z, Fahmy K, Rashidian A, Hajjeh R. Capacity-building for conducting COVID-19 vaccine effectiveness studies to enhance evidence-informed vaccination policymaking in the Eastern Mediterranean Region. East Mediterr Health J [Internet]. 2023;29(7):562\u0026ndash;9. Available from: https://pubmed.ncbi.nlm.nih.gov/37553744/\u003c/li\u003e\n\u003cli\u003eKarimian Z, Bellizzi S, Sirous S, Lukwiya M, Ahmed A, Fahmy K, et al. 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Available from: https://pubmed.ncbi.nlm.nih.gov/37317681/\u003c/li\u003e\n\u003cli\u003eSalem GM, Said RM, Abdelsalam AE. Acceptance rate of COVID-19 vaccination and its predictors in Egypt: An online survey. The Journal of Infection in Developing Countries [Internet]. 2022 Jun 30;16(06):993\u0026ndash;1000. Available from: https://jidc.org/index.php/journal/article/view/35797293\u003c/li\u003e\n\u003cli\u003eFares S, Elmnyer MM, Mohamed SS, Elsayed R. COVID-19 Vaccination Perception and Attitude among Healthcare Workers in Egypt. J Prim Care Community Health. 2021;12. \u003c/li\u003e\n\u003cli\u003eTharwat S, Nassar DK, Nassar MK, Saad AM, Hamdy F. Attitude towards COVID-19 vaccination among healthcare workers: a cross sectional study from Egypt. BMC Health Serv Res [Internet]. 2022;22(1):1357. Available from: https://doi.org/10.1186/s12913-022-08751-3\u003c/li\u003e\n\u003cli\u003eDevelopment and Licensure of Vaccines to Prevent COVID-19 | FDA [Internet]. [cited 2024 Aug 19]. Available from: https://www.fda.gov/regulatory-information/search-fda-guidance-documents/development-and-licensure-vaccines-prevent-covid-19\u003c/li\u003e\n\u003cli\u003eInterim analysis of COVID-19 vaccine effectiveness against Severe Acute Respiratory Infection due to SARS-CoV-2 in individuals aged 20 years and older \u0026ndash; fourth update [Internet]. [cited 2024 Aug 19]. Available from: https://www.ecdc.europa.eu/en/publications-data/interim-analysis-covid-19-vaccine-effectiveness-against-severe-acute-respiratory\u003c/li\u003e\n\u003cli\u003ePratama NR, Wafa IA, Budi DS, Sutanto H, Asmarawati TP, Barlian Effendi G, et al. Effectiveness of COVID-19 Vaccines against SARS-CoV-2 Omicron Variant (B.1.1.529): A Systematic Review with Meta-Analysis and Meta-Regression. Vol. 10, Vaccines. MDPI; 2022. \u003c/li\u003e\n\u003cli\u003eFerdinands JM, Rao S, Dixon BE, Mitchell PK, Desilva MB, Irving SA, et al. Waning of vaccine effectiveness against moderate and severe covid-19 among adults in the US from the VISION network: Test negative, case-control study. The BMJ. 2022; \u003c/li\u003e\n\u003cli\u003eSilveira MM, Moreira GMSG, Mendon\u0026ccedil;a M. DNA vaccines against COVID-19: Perspectives and challenges. Life Sci [Internet]. 2021;267:118919. Available from: https://www.sciencedirect.com/science/article/pii/S0024320520316799\u003c/li\u003e\n\u003cli\u003eClerici B, Muscatello A, Bai F, Pavanello D, Orlandi M, Marchetti GC, et al. Sensitivity of SARS-CoV-2 Detection With Nasopharyngeal Swabs. Front Public Health. 2021 Jan 26;8. \u003c/li\u003e\n\u003cli\u003eTracking SARS-CoV-2 variants [Internet]. [cited 2024 Aug 19]. Available from: https://www.who.int/activities/tracking-SARS-CoV-2-variants\u003c/li\u003e\n\u003cli\u003eImmunization and Respiratory Diseases (NCIRD) Overview | CDC [Internet]. [cited 2024 Aug 19]. Available from: https://www.cdc.gov/ncird/overview/index.html\u003c/li\u003e\n\u003cli\u003eHe Z, Ren L, Yang J, Guo L, Feng L, Ma C, et al. Seroprevalence and humoral immune durability of anti-SARS-CoV-2 antibodies in Wuhan, China: a longitudinal, population-level, cross-sectional study [Internet]. Vol. 397, www.thelancet.com. 2021. Available from: http://www.nhc.gov.cn/xcs/\u003c/li\u003e\n\u003cli\u003eAlfego D, Sullivan A, Poirier B, Williams J, Grover A, Gillim L, et al. A population-based analysis of the longevity of SARS-CoV-2 antibody seropositivity in the United States. EClinicalMedicine [Internet]. 2021 Jun 1;36. Available from: https://doi.org/10.1016/j.eclinm.2021.100902\u003c/li\u003e\n\u003cli\u003ePeluso MJ, Takahashi S, Hakim J, Kelly JD, Torres L, Iyer NS, et al. SARS-CoV-2 antibody magnitude and detectability are driven by disease severity, timing, and assay. Sci Adv [Internet]. 2024 Aug 19;7(31):eabh3409. Available from: https://doi.org/10.1126/sciadv.abh3409\u003c/li\u003e\n\u003cli\u003eCoronavirus Disease 2019 (COVID-19) | COVID-19 | CDC [Internet]. [cited 2024 Aug 19]. Available from: https://www.cdc.gov/covid/?CDC_AAref_Val=https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/vaccine-induced-immunity.html%25201/16\u003c/li\u003e\n\u003cli\u003eGudbjartsson DF, Norddahl GL, Melsted P, Gunnarsdottir K, Holm H, Eythorsson E, et al. Humoral Immune Response to SARS-CoV-2 in Iceland. New England Journal of Medicine. 2020 Oct 29;383(18):1724\u0026ndash;34. \u003c/li\u003e\n\u003cli\u003eWang H, Yuan Y, Xiao M, Chen L, Zhao Y, Haiwei Zhang, et al. Dynamics of the SARS-CoV-2 antibody response up to 10 months after infection. Cell Mol Immunol. 2021 Jul 1;18(7):1832\u0026ndash;4. \u003c/li\u003e\n\u003cli\u003eWei J, Matthews PC, Stoesser N, Maddox T, Lorenzi L, Studley R, et al. Anti-spike antibody response to natural SARS-CoV-2 infection in the general population. 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Available from: https://doi.org/10.1016/j.lana.2022.100212\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-infectious-diseases","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"infd","sideBox":"Learn more about [BMC Infectious Diseases](http://bmcinfectdis.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/infd","title":"BMC Infectious Diseases","twitterHandle":"#bmcinfectdis","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"COVID-19, vaccine effectiveness, binding antibodies, RT‒PCR, health workers, cohort study","lastPublishedDoi":"10.21203/rs.3.rs-5754076/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5754076/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eObjective:\u003c/strong\u003e A cohort study was conducted with the support of the WHO, where a standardized WHO protocol was followed to measure vaccine effectiveness (VE) against symptomatic RT‒PCR confirmed SARS‒CoV-2 infection among hospital health workers (HWs) eligible for vaccination at Al-Azhar University hospitals.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods:\u003c/strong\u003e A WHO-supported cohort study was conducted from July 2022 through September 2023 and included 1249 HWs who were randomly selected and followed up biweekly for one year. At enrollment, nasopharyngeal (NP) and blood samples were collected from each participant and evaluated to detect SARS-CoV-2 RNA via a real-time PCR assay (QIAGEN) and for the quantitative detection of SARS-CoV-2-binding antibodies via the Roche Elecsys Anti-SARS-CoV-2 S immunoassay (Roche Diagnostics, GmbH, Germany). During follow-up, NP samples were collected from anyone who developed symptoms consistent with the WHO definition of suspected cases of SARS-CoV-2 infection.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults:\u003c/strong\u003e At enrollment, SARS-CoV-2 RNA was detected in 119/1235 (9.6%) HWs and 89% of the participants with positive RNA were asymptomatic. COVID-19-binding antibodies were detected among 1245/1248 HWs (99.8%), and 53.2% had titers \u0026gt; 2500, regardless of vaccination status. During follow-up, 232 participants had COVID-19 symptoms, but only 109 provided NP samples, and 18 of them were positive for SARS-CoV-2 RNA. No hospitalization or mortality was recorded\u003cdel\u003e \u003c/del\u003eat enrollment or during the follow-up period. The cumulative incidence of COVID-19 infection was higher among HWs with incomplete vaccination compared to unvaccinated, fully vaccinated, or those who received booster doses (P =0.025). There was no significant difference in VE among HWs who were fully vaccinated or had booster doses compared with unvaccinated HWs, with adjusted VE values of 68% (95% CI -28% to 92%) and 64% (95% CI -170% to 95%), respectively (P = 0.106 and 0.318 respectively). The adjusted VE increased to 89% (95% CI -33% to 99%) among HWs with hybrid immunity compared with those who were unvaccinated with a previous COVID-19 infection (P =0.082).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study indicates that VE was higher among HWs with hybrid immunity compared to unvaccinated HWs with previous COVID-19 infection. The findingsalso highlight the importance of completing the primary vaccination series against COVID-19. This study reveals a high rate of asymptomatic COVID-19, a lower rate of confirmed cases, and a marked decrease in hospitalization and fatality rates at enrollment and during follow-up. Real-world VE studies are in need to address many unanswered questions, including the appropriate number of booster doses, duration of protection, and incidence of vaccine adverse events.\u003c/p\u003e","manuscriptTitle":"Assessing SARS-CoV-2 Vaccine Effectiveness in Health Workers: A Cohort Study in Five Al-Azhar University Hospitals, Egypt","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-03-31 06:31:39","doi":"10.21203/rs.3.rs-5754076/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-04-17T05:55:20+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"298902769900725950577649970197240269437","date":"2025-04-17T00:47:14+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-16T05:02:47+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"81504931202450637961218450303097200216","date":"2025-04-15T15:33:29+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-03-28T12:28:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"183234040767135698165640891466002840700","date":"2025-03-28T12:17:07+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"94315896000552447762286064091829086331","date":"2025-03-27T12:03:06+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-03-27T10:43:47+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-03-27T06:19:53+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Infectious Diseases","date":"2025-03-24T20:54:22+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-infectious-diseases","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"infd","sideBox":"Learn more about [BMC Infectious Diseases](http://bmcinfectdis.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/infd","title":"BMC Infectious Diseases","twitterHandle":"#bmcinfectdis","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"08aa055c-2fdb-487b-a084-a9e7fd9017cb","owner":[],"postedDate":"March 31st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-09-29T16:03:41+00:00","versionOfRecord":{"articleIdentity":"rs-5754076","link":"https://doi.org/10.1186/s12879-025-11446-9","journal":{"identity":"bmc-infectious-diseases","isVorOnly":false,"title":"BMC Infectious Diseases"},"publishedOn":"2025-09-26 15:57:50","publishedOnDateReadable":"September 26th, 2025"},"versionCreatedAt":"2025-03-31 06:31:39","video":"","vorDoi":"10.1186/s12879-025-11446-9","vorDoiUrl":"https://doi.org/10.1186/s12879-025-11446-9","workflowStages":[]},"version":"v1","identity":"rs-5754076","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5754076","identity":"rs-5754076","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}