Seroprevalence of measles-specific IgG and genotype-specific neutralizing antibody responses in clinically confirmed cases during the 2021–2023 measles outbreaks in Liberia

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Donzo, Nicola Logan, TROY D. MOON, Ralph W. Jetoh, Margaret J. Hosie, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9210123/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background Since 2021, Liberia has experienced disruptive outbreaks of measles across all of its 15 counties, despite the availability of a safe, effective vaccine. There is no data on the potential role of vaccine-induced immunity and no study on seroprevalence of measles-specific IgG in Liberia. Furthermore, there is no data on genotype-specific variation in antibody effectiveness in Liberia. This study evaluated the seroprevalence of measles virus (MeV)-specific IgG in clinically diagnosed patients in Liberia and assessed the breadth of neutralization against four genotypes. Methods Samples collected retrospectively from 2021 to 2023 and prospective samples collected in 2023 from clinically diagnosed measles cases were analyzed in this study. Study participants included both vaccinated and unvaccinated individuals. MeV-specific IgG antibody was assessed using an enzyme-linked immunosorbent assay. Neutralizing antibodies against the Edmonston, B3, D4, and D8 MeV genotypes were measured using vesicular stomatitis virus pseudotype-based neutralization assays. Results Overall, 69.9% of 199 individuals, including 100 vaccinees that were clinically diagnosed with measles, tested positive for MeV-specific IgG antibodies. MeV-specific IgG positivity was higher in vaccinated (52.5%) than in unvaccinated individuals (8.6%). Strong neutralization was observed against the D8 genotype in 98.9% of seropositive individuals, compared to 94.7% against Edmonston and D4 genotypes and 91.6% against B3. Significantly higher neutralization titers were observed in vaccinated compared to unvaccinated individuals for all four genotypes (p < 0.0001). There was a weak positive correlation between IgG levels, neutralizing titers, and participant age. Conclusion The findings demonstrate strong genotype-cross-neutralizing immunity among vaccinated and seropositive patients, highlighting the critical role of measles vaccination in maintaining effective antibody protection. The significant percentage of seronegative patients indicates ongoing vulnerability to measles transmission and reinforces the need to improve vaccination coverage. Measles virus outbreak MeV-specific IgG neutralizing antibody clinically-confirmed cases seroprevalence Liberia neutralization breadth measles containing vaccine genotype–cross-neutralizing Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 BACKGROUND Measles is a highly contagious airborne viral infection caused by measles virus (MeV) resulting in severe complications and sometime death. These severe complications are predominantly in young children due to immature immunity, waning maternal antibodies, and delayed vaccination ( 1 ). MeV is spread through respiratory droplets, and clinical symptoms typically include high fever, cough, conjunctivitis, and a characteristic maculopapular rash. Measles symptoms typically develop 10–14 days after exposure to the virus. The World Health Organization (WHO) case definition of measles categorizes a suspected case as a patient having a temperature over 38°C and a maculopapular rash. According to WHO, a clinical case of measles is defined as any patient presenting with a fever, a maculopapular rash, and at least one of the following symptoms: cough, coryza, or conjunctivitis. Despite the availability of safe and effective vaccines, measles continues to pose a significant global health challenge. In 2023, over 107,500 measles-related mortalities occurred globally, largely among unvaccinated children under five years of age. In 2022, Measles Containing Vaccine dose 1 (MCV1) coverage declined to 83% globally, its lowest since 2008 ( 2 ). In Liberia, MCV1 coverage increased from 58% in 2021 to 82% in 2023, and MCV2 from 50% in 2019 to 60% in 2023 ( 3 ). However, Liberia has experienced a nationwide outbreak since 2021, with 14,192 confirmed cases and 98 deaths reported as of December 14, 2025 ( 4 ). The B3 genotype remains the predominant endemic measles virus lineage circulating in sub-Saharan Africa, with sustained transmission documented across Western and Central Africa ( 5 ). This genotype has been repeatedly reported in Nigeria, Ghana, Cameroon, and The Gambia, reflecting its long-standing regional establishment ( 5 ). In contrast, the D4 and D8 genotypes show greater genetic heterogeneity and are more often associated with outbreaks and importation events, particularly in eastern and southern parts of the continent ( 6 ). D4 genotypes have been detected in countries such as Uganda, Tanzania, and South Africa, with many reports suggesting importation or short-term regional dissemination rather than persistent endemic circulation ( 6 ). Similarly, D8 genotype viruses have been identified in South Africa and Zimbabwe in recent surveillance years, although their occurrence has varied from year to year, indicating sporadic introductions rather than continuous transmission ( 6 ). Serological surveillance is crucial for ascertaining immunity gaps and evaluating vaccination program performance. IgG seroprevalence surveys help assess population protection, while neutralization assays are crucial for measuring functional immunity, as Enzyme-Linked Immunosorbent Assay (ELISA) cannot differentiate neutralizing from non-neutralizing antibodies ( 4 – 5 ). Neutralizing antibodies targeting MeV hemagglutinin (H) and fusion (F) proteins are key to protection and reflect the antigenic variability of circulating genotypes ( 6 , 7 , 8 ). Previously, studies have shown genotype-specific differences in neutralizing responses. Lower titers against MeV genotype A compared with D4 and D8, reduced titers against genotype B3 in Iran, and variable responses across genotypes in the United Kingdom (UK) demonstrate the importance of assessing genotype-specific immunity (10–12, 34). Liberia introduced MCV1 in 1978 and MCV2 in 2019, but there is no data on measles IgG seroprevalence, vaccine-induced immunity, or genotype-specific neutralization. This study aimed to assess MeV-specific IgG seroprevalence in clinically confirmed measles patients and to evaluate the neutralization breadth of MeV-specific IgG against four genotypes during Liberia’s ongoing outbreak. METHODS Study Design and Subject Selection Criteria The study employed a cross-sectional design that consisted of two components: a retrospective evaluation using whole-blood samples obtained from individuals meeting the suspected case definition for MeV stored at the National Reference Laboratory of Liberia from December 2021 to August 2023 and a prospective study that collected samples from March 2023 to June 2023 of clinically diagnosed MeV patients at the Redemption Hospital in Monrovia, Liberia. Separation of Plasma and Sera from Whole Blood. We collected whole blood using BD Vacutainer® cell preparation tubes, centrifuged for 30 minutes at 1800 x g at room temperature. Plasma was then transferred into 2 mL tubes and stored at − 80°C. Enzyme-Linked Immunosorbent Assay (ELISA) All samples were brought to 25°C, and MeV-specific IgG was quantified using a commercial ELISA kit (SERION ELISA classic measles virus IgG) according to the manufacturer’s instructions. The commercial ELISA kit uses recombinant MeV nucleoprotein derived from the Edmonston strain. Samples were diluted 1:100 (5 µL sample + 495 µL diluent), loaded with controls onto 96-well plates, and the plates were incubated for 60 minutes at 37°C. After the washing steps, plates were incubated for 30 minutes with anti-human IgG conjugate at 37°C and washed again. The substrate solution containing para-nitrophenylphosphate was added and incubated for 30 minutes at 37°C. The reaction was stopped using 1.2 N NaOH, and optical density was measured at 405 nm. Antibody titers (mIU/mL) were calculated using the manufacturer’s calibration specifications, with serostatus defined as 200 (positive). A positive IgG result indicated prior infection or vaccination. Cell Lines and Viruses Human embryonic kidney (HEK) 293T cells were cultured and engineered to express the human SLAM1 receptor under standard culture conditions as described by Logan et al. SLAM1 (CD150), expressed on immune cells, is the primary receptor for wild-type MeV. Cells were cultured and maintained in DMEM supplemented with 10% FBS, 100 IU/mL penicillin-streptomycin, and 2 mM L-glutamine. For stable selection, HEK 293 SLAM1 cells were grown in medium containing 1 µg/mL puromycin and HEK 293T cells with 400 µg/mL G418. These conditions ensured consistent SLAM1 expression and reliable experimental performance. All reagents were provided by Hosie’s and Willett’s laboratories at the Centre for Virus Research, University of Glasgow. Production of Vesicular Stomatitis Virus ΔG (VSV ΔG) MeV Pseudovirus The VSV ΔG–MeV pseudoviruses were generated using four MeV genotypes (Edmonston, B3, D8, and D4). Plasmid vectors encoding each genotype’s H and F glycoproteins were synthesized, and pseudoviruses were produced by transfecting 2 × 10⁶ HEK 293T cells with 5 µg each of H and F plasmids. After 4 hours, cells were infected with VSV ΔG Luc (1.15 × 10⁷ TCID₅₀; MOI 0.02) for 1 hour, then washed and incubated in 10 mL DMEM for 48 hours at 37°C/5% CO₂. Supernatants were then filtered through a 0.45 µm filter, and viral titers were determined by TCID₅₀ on HEK 293 SLAM1 cells. Pseudotype-Based Neutralization Assay The retrospective and prospective serum samples were serially diluted 4‑fold from 1:16 to 1:32,768, and the diluted sera were incubated in triplicate with 2.5 × 10³ TCID₅₀ of pseudotyped virus in 96‑well plates for 1 hour at 37°C/5% CO₂. Afterward, 2 × 10⁴ HEK 293 SLAM1 cells were added and incubated on plates for 48 hour before adding Steadylite Plus™ luciferase substrate and measuring luminescence on a Revvity EnSight® plate reader. Data and Statistical Analysis All data were analysed using GraphPad Prism 7.01 (GraphPad Software, San Diego, CA, USA) and R 4.3.1 (R Development Core Team, including ggplot2 for visualization). MeV‑specific IgG levels were compared between vaccinated and unvaccinated groups using the two‑tailed Mann–Whitney U test. Neutralizing antibody responses to the three wild-type genotypes (B3, D4, and D8) were evaluated in comparison with the vaccine genotype, Edmonston. A WHO reference serum product number NIBSC code 97/648 (3000 mIU/mL; protective level 125 mIU/mL) was diluted and included to define the protective threshold—the minimum measles-specific antibody level that confers protective immunity—in the pseudotype assay. Median neutralizing titers across genotypes were compared using the Kruskal–Wallis test and vaccinated versus unvaccinated titers were analyzed using the Wilcoxon matched‑pairs signed rank test. Spearman's rank correlation was used to assess the relationships between IgG status and age, as well as the associations between Edmonston, B3, D4, and D8 neutralization titers and age. Statistical significance was set at p-value < 0.05. RESULTS Demographics Characteristics A total of one hundred and ninety-nine (199) samples were analysed for MeV-specific IgG (Table 1 ). Participant characteristics varied by vaccination status. Sex distribution did not differ significantly between groups (p-value = 0.50). There were statistically significant differences in age groups (p-value < 0.001): vaccinated participants were mainly 11–20 years old, while unvaccinated participants were also concentrated in this age range, and those with unknown status were mostly younger (< 5 years and 5–10 years). Sample type exhibited statistically significant differences (p-value < 0.001), with all unvaccinated participants drawn from prospective samples and all with unknown status from retrospective samples. Clinical presentations were similar, as all participants reported fever and maculopapular rash, with no differences between groups (fever: p-value = 1.0; rash: p-value = 1.0). Table 1 Demographic, and clinical characteristics of participants. *Characteristics* N Vaccinated N = 100 1 Unvaccinated N = 17 1 Unknown N = 82 1 p-value 2 Sex 199 0.5 Female 62 (62.0%) 8 (47.1%) 48 (58.5%) Male 38 (38.0%) 9 (52.9%) 34 (41.5%) Age Group 199 < 0.001 < 5 yrs 8 (8.0%) 4 (23.5%) 34 (41.5%) 5–10 yrs 21 (21.0%) 2 (11.8%) 23 (28.0%) 11–20 yrs 34 (34.0%) 8 (47.1%) 15 (18.3%) 21–30 yrs 19 (19.0%) 3 (17.6%) 7 (8.5%) 31–56 yrs 18 (18.0%) 0 (0.0%) 3 (3.7%) Sample Type 199 < 0.001 Prospective 86 (86.0%) 17 (100.0%) 0 (0.0%) Retrospective 14 (14.0%) 0 (0.0%) 82 (100.0%) Fever 199 1.0 Yes 100 (100.0%) 17 (100.0%) 82 (100.0%) Maculopapular Rash 199 1.0 Yes 100 (100.0%) 17 (100.0%) 82 (100.0%) Cough 199 0.11 Yes 97 (97.0%) 17 (100.0%) 74 (90.2%) No 3 (3.0%) 0 (0.0%) 8 (9.8%) Conjunctivitis 199 0.2 Yes 37 (37.0%) 3 (17.6%) 33 (40.2%) No 63 (63.0%) 14 (82.4%) 49 (59.8%) 1 n (%) 2 Pearson's Chi-squared test; Fisher's exact test Seroprevalence of Measles-Specific IgG Out of 199 samples tested for MeV-specific IgG, 139 participants (69.9%) were IgG seropositive, with smaller proportions being seronegative (23.1%) or equivocal (7.0%) (Fig. 1 a). The IgG status among participants varied by age group. Seronegativity was highest among children < 5 years of age (39.1%) with 19.4% being seropositive and 7.1% being equivocal. In the 5–10-year age group, seronegativity remained common (19.6%), while seropositivity increased to 23% and 37.5% were equivocal. Adolescents aged 11–20 years recorded the highest proportion of seropositive samples (27.3%), with 26.1% being seronegative, and 50% equivocal. Older adults aged 21–30 years showed lower seropositivity (16.6%) and no equivocal results, whereas those aged 31–56 years of age displayed a modest increase in seropositivity (13.7%) alongside low levels of seronegativity and equivocal findings (Fig. 1 b). Gender differences were observed in seroprevalence of IgG (Fig. 1 c). Female participants exhibited a higher proportion of seropositivity (43.2%) compared with male participants (26.6%), while sero-negativity and equivocal proportions were broadly similar between genders (Fig. 1 c). Vaccination status was strongly correlated with being IgG seropositive (Fig. 1 d). Vaccinees had the highest rate of seropositivity (52.5%) while unvaccinated participants demonstrated a decreased seropositivity rate (8.6%) (Fig. 1 d). MeV-specific IgG concentration levels did not differ significantly between vaccinated and unvaccinated individuals (p = 0.21; Fig. 2 a). Similarly, no statistically significant differences in MeV-specific IgG levels were observed across age groups (> 5 years, 5–10 years, 11–20 years, 21–30 years, and 31–56 years; Fig. 2 b). Although not statistically significant, there was a modest trend toward higher seropositivity with increasing age and vaccination status. Neutralizing Antibody Responses to Four MeV genotypes in Seropositive Individuals The percentage of seropositive individuals with neutralizing antibody titers was determined for the four genotypes; our results revealed that 94.7% of seropositive individuals tested demonstrated neutralization titers against Edmonston, 91.6% against B3, 94.7% against D4, and 98.9% against D8 (Table 2 ). Also, we compared MeV-neutralizing antibody titres between three wild-type genotypes (B3, D4, and D8) and vaccine genotype, Edmonston. Our findings revealed that B3 and D8 have significantly higher titers than Edmonston, while D4 has the lowest median neutralizing titer, with more participants below the protective threshold (Fig. 3 ). Table 2 The percentage of seropositive individuals with neutralizing titers exceeding the protective threshold. Genotype Percentage Protected (%) Edmonston 94.7 B3 91.6 D4 94.7 D8 98.9 Comparison of MeV neutralization titers with vaccination status For all MeV genotypes assessed, vaccinated individuals displayed higher neutralization titers compared with the unvaccinated participants. This trend was the same for vaccine strain (Edmonston) as well as circulating wild-type B3, D4, and D8 genotypes tested (Fig. 4 a-d). Correlation between Age and measles-specific IgG on Neutralizing Antibody Titers Neutralization titers against the Edmonston genotype showed a weak but statistically significant positive correlation with increasing age (Fig. 5 a). Similarly, neutralization titers against the B3 and D4 genotypes showed a weakly positive correlation with increasing age, though neither was statistically significant (Figs. 5 b and 5 c). Since not all IgG antibodies neutralize, and low IgG still corresponds to neutralizing activity, we subsequently assessed the correlation between measles-specific IgG concentrations and neutralization titers. There was a moderate positive correlation between neutralization titers against D4, Edmonston, and measles IgG antibodies that was strongly statistically significant (Figs. 6 a and 6 c). The correlation between neutralization titers against D8, B3, and measles IgG antibodies ranged from moderate to strong and weak to moderate positive correlation, respectively (Figs. 6 b and 6 d). DISCUSSION Seroprevalence studies offer critical understanding of the transmission patterns and population-level impact of infectious diseases. By measuring pathogen-specific antibodies, they can help in identifying previous exposure, estimate progress toward herd immunity thresholds, and guide public health interventions. Neutralizing antibody titers, in particular, are widely considered robust correlates of protective immunity, with higher titers generally associated with reduced risks of reinfection and severe disease. Although genotypes responsible for the current outbreak have not been identified, B3 was believed to be circulating in the West African region, including Liberia, in 2010 ( 5 ). Previous studies have shown substantial differences in the seroprevalence of measles IgG in different settings. Zahoor et al. ( 8 ) and Adekola et al. ( 9 ) reported seroprevalence around 73.48% and 29.2% while Inuwa et al. ( 10 ) and Smetana et al. ( 11 ) found levels of seroprevalence of 61.6% and 70%. In contrast, significantly higher seroprevalences of measles IgG, ranging from 92% to 99%, were reported in the DRC ( 12 ), other African settings ( 13 ), China ( 14 ) and Vietnam ( 15 ). These variances likely reflect differences in national vaccination efficacy, historical patterns of measles transmission, and the role of natural infection in population immunity ( 16 ). The present study found an overall seroprevalence of 69.9%, with a seropositivity rate of just 52.5% among vaccinated individuals, suggesting immunity gaps in Liberia. The relatively low coverage of MCV1 and particularly MCV2 in Liberia could be contributing to these gaps, underscoring the need for strengthened routine vaccination and targeted strategies. Further study is necessary to understand the underlying factors contributing to low immunity, despite an MCV1 coverage of roughly 82%. Naturally acquired immunity also affects seroprevalence patterns. In some regions, unvaccinated individuals, especially those aged 30 and above, have seroprevalence that sometimes exceeds 95%, mostly attributable to past encounters with MeV ( 13 ). However, some studies like Manirakiza et al. ( 17 ) showed a decline in measles immunity among specific populations despite vaccination programs, highlighting continued susceptibility in some demographic groups. In contrast to these studies, the present study found significant age-related differences in seropositivity with decreased immunity in children under 5, young adults (21–30 years), and adults (31–56 years). Decreased seropositivity in young infants may indicate limited vaccination coverage or waning of maternal antibodies. Stronger or higher titers among school-aged children and teenagers suggest stronger vaccine-derived protection in these demographics as compared to younger children and adults. Together, these findings highlight a changing landscape of susceptibility to measles, with increasing vulnerability in infants and older adults. Age-specific differences influence epidemic risk, especially in areas with low vaccination rates or late second-dose administration. Enhancing regular vaccination, improving maternal immunity, and bolstering catch-up campaigns for adolescents and young adults may be critical for attaining and maintaining measles eradication goals. Earlier studies have consistently demonstrated waning neutralizing antibodies post-MMR vaccination, prompting concerns over long-term protection. An observational study of adolescents and young adults found that only 23.2% of individuals vaccinated with two doses of MMR maintained antibody levels above the protective threshold 7.4 years later, compared to 8.6% seropositivity among unvaccinated individuals ( 19 ). Modelling-based analyses have indicated annual declines of 9.7% in neutralizing antibodies following the first dosage of MMR and 4.8% after the second dose of MMR ( 20 ). Data from the United States similarly found a seronegativity rate of 33% two decades after MMR vaccination ( 21 ). These findings are consistent with the present study’s findings and collectively highlight an increasing risk among vaccinated populations and indicate a necessity to more accurately identify individuals who have titers below protective levels. The declines in neutralizing titers observed in earlier studies align with the present study’s finding. Decreased protective titers seen in individuals may suggest limited exposure or suboptimal immune responses to past vaccinations ( 18 ). These data collectively emphasize the need for enhanced monitoring of post-vaccination immunity and more study to elucidate the drivers and clinical consequences of declining measles antibodies. Sero-epidemiological studies have also indicated considerable geographical variation in measles susceptibility. For example, a serosurvey in Romania has revealed a measles seronegativity of 23% ( 22 ), while a cross-sectional survey in Oman identified an even greater susceptibility among individuals aged 15–20 years ( 23 ). In contrast, lower seronegativity (12.3%) among vaccinees has been reported in Iran ( 24 ). Ristić et al. has also found a susceptibility threshold above WHO’s recommended susceptibility threshold of ≤ 5%. In the Central African Republic, only 51.3% and 27.6% had detectable measles IgG among vaccinees and unvaccinated individuals, respectively ( 17 ). The seronegativity rate of 23.12% found in the present study among participants aligns with these data, suggesting that approximately 1 in 4 participants lacked protective antibodies. Particularly concerning was the low seropositivity (52.5%) among vaccinated participants, despite Liberia’s reported MCV1 coverage of approximately 82%. Sex-related differences in vaccine-induced immune responses have been reported. Females tend to generate larger measles-specific antibody titers post-vaccination, whereas males may have a more rapid reduction in these titers ( 25 ). Evidence from various settings corroborates these trends. For instance, studies from India ( 26 ), Europe ( 27 ) and the US ( 14 ) agreed with these trends. The present study found higher seropositivity among females (43.2%) than males (26.5%) consistent with this pattern. Additionally, across-sectional study of children above 15 years who received the MMR vaccine at 12–15 months indicated significantly higher prevalence of measles-specific IgG antibodies in females than in males ( 28 ). A regression analyses identified age at vaccination and female sex as the two principal determinants of long-term antibody persistence following MMR vaccination ( 29 ). These demographic differences are epidemiologically crucial for maintaining long-term protection against measles. The lower seropositivity seen in men may result in small yet epidemiologically important zones of susceptibility that might facilitate continued viral transmission. The high transmissibility of measles exacerbates the risk of outbreaks due to immunization gaps. To maintain herd immunity and avert a recurrence of measles, it is imperative to implement improved monitoring of male immunity and to conduct targeted vaccinations as necessary. This study showed that participants mounted strong neutralizing responses against all four tested MeV genotypes. Titers were significantly higher for B3 as compared to Edmonston, suggesting that wild-type viruses may elicit more robust humoral responses than the attenuated vaccine lineage. Genotype D8 also produced higher titers than D4, indicating genotype-specific differences despite overall antigenic conservation. These findings align with reports of broad cross-neutralization among Edmonston, D4, and D8 ( 30 ), though variability has been noted, such as lower B3 titers in vaccinated individuals in Iran compared with H1, D4, and A genotypes ( 31 ). Further work is needed to understand molecular and structural drivers underlying the stronger responses observed for B3 and D8. Conclusions The findings demonstrate strong genotype–cross neutralizing immunity among vaccinated and seropositive patients, highlighting the critical role of measles vaccination in maintaining effective antibody protection. However, the higher titers against wild-type strains compared to the vaccine strain raises concerns regarding the long-term durability of vaccine-induced immunity. The significant percentage of seronegative patients in our study indicates ongoing vulnerability to measles transmission and reinforces the need to improve vaccination coverage. Abbreviations DRC: Democratic Republic of Congo DMEM: Dulbecco’s Modified Eagle Medium EIA: Enzyme Immuno-assay ELISA: Enzyme-Linked Immuno Assay FBS: Fetal Bovine Serum HEK: Human embryonic kidney HRP: Horseradish peroxidase IgG: Immunoglobulin G IgM: Immunoglobulin M IRB: Institutional Review Board MCV: Measles Containing Vaccine MCV1: Measles Containing Vaccine 1 MCV2: Measles Containing Vaccine 2 MeV: Measles Virus MOI : Multiplicity of Infection MRC: Medical Research Council NPHIL: National Public Health Institute of Liberia NPHRL: National Public Health Reference Laboratory OD: Optic density PNA: Pseudovirus Neutralization Assay PREVSL: Partnership for Research in Emerging Viral Infections Sierra Leone PRNT: Plaque Reduction Neutralization Test SLAM: Signaling Lymphocytic Activation Molecule UK: United Kingdom VSVΔG: Vesicular Stomatitis Virus Delta G WACCBIP: West African Centre for Cell Biology of Infectious Pathogens WHO: World Health Organization Declarations Funding This research was funded in part by Science for Africa Foundation to the Developing Excellence in Leadership, Training and Science in Africa (DELTAS Africa) programme [DEL-22-014] with support from Wellcome and the UK Foreign, Commonwealth & Development Office and is part of the EDCPT2 programme supported by the European Union. This work was also supported by a fellowship to KSD from a World Bank African Centres of Excellence grant (WACCBIP+NCDs: Awandare). In addition, research reported in this publication was supported by the Fogarty International Center of the National Institutes of Health under Award Number U2RTW011248. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Funders. For purposes of open access, the author has applied a CC BY public copyright licence to any Author Accepted Manuscript version arising from this submission. Data Availability All data supporting this study conclusion are all included within the article. Additional datasets are available from the corresponding author upon request. Authors information This work was supervised by Prof. Kwadwo Asamoah Kusi, Prof. Peter Kojo Quashie, NMIMR, and WACCBIP, Prof. Troy D. Moon, Department of Tropical Medicine and Infectious Diseases, Tulane University, Prof. Margaret J. Hosie, Prof. Brian J. Willett, and Nicola Logan from the and MRC–University of Glasgow Centre for Virus Research, and Dr. Ralph W. Jetoh fromNational Public Health Institute of Liberia, Oldest Congo Town, Monrovia, Liberia. Acknowledgement I am grateful to NPHIL for providing all the retrospective samples and all the participants and their families who participated in this study for their time, cooperation, and trust. I am also grateful to the management and staff of Redemption Hospital for their assistance in collecting the prospective samples at the hospital. I wish to express my sincere appreciation to Prof. Margaret J. Hosie, Prof. Brian J. Willett, Nicola Logan, and all members of the Hosie Laboratory at the MRC–University of Glasgow Centre for Virus Research for their generous guidance, assistance, and support throughout my stay. Authors and Affiliations West African Centre for Cell Biology of Infectious Pathogens, University of Ghana, Legon-Accra, Ghana Kalilu S Donzo and Prof. Peter Kojo Quashie Department of Biochemistry, Cell, and Molecular Biology, University of Ghana, Legon-Accra, Ghana Kalilu S Donzo Immunology Department, Noguchi Memorial Institute of Medical Research, College of Health Sciences, University of Ghana, Accra, Ghana Prof. Kwadwo Asamoah Kusi MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland Prof. Margaret J. Hosie, Prof. Brian J. Willett, and Nicola Logan Tulane University School of Public Health and Tropical Medicine, New Orleans, Louisiana Prof. Troy D. Moon National Public Health Institute of Liberia, Oldest Congo Town, Monrovia, Liberia Dr. Ralph W. Jetoh Contributions KAK, PKQ, and K.S.D. contributed to the design and conceptualization of the study; K.S.D. and R.W.J. contributed to sample collection and processing. K.S.D. performed the ELISA and data analysis and drafted the manuscript. K.S.D. and N.L. performed and assisted with the PNA assay, and B.J.W. and M.J.H. assisted with PNA data analysis. K.A.K., PKQ, T.D.M., M.J.H., B.J.W., and N.L. provided resources and contributed to data interpretation, writing, review, and editing of the manuscript. All authors read and approved the final version. Corresponding authors Correspondence to Kwadwo Asamoah Kusi and Kalilu S. Donzo Ethics declarations Ethics approval and consent to participate The study received ethical approval from the University of Liberia Institutional Review Board (ULIRBIORG-IRB Number: IRB00013730) and the Noguchi Memorial Institute for Medical Research Institutional Review Board (NMIMR-IRB 0000908). All identifying details, including names and addresses, were removed before data analysis to ensure confidentiality. The collected data was then stored in a secure folder. The study was conducted in accordance with the ethical principles of the Declaration of Helsinki. Written informed consent and assent were obtained from the parents or legal guardians of all participating children. Consent for publication All authors have reviewed and approved the final version of this manuscript. We confirm that every author has agreed to its submission and consents to its publication. Competing interests The authors declare no competing interests. References CDC. Measles (Rubeola). 2025 [cited 2025 Mar 8]. Clinical Overview of Measles. Available from: https://www.cdc.gov/measles/hcp/clinical-overview/index.html WHO. Measles [Internet]. 2024 [cited 2025 Oct 30]. Available from: https://www.who.int/news-room/fact-sheets/detail/measles Masresha BG, Shibeshi ME, Grant GB, Hatcher C, Wiysonge CS. Progress with the Second Dose Measles Vaccine Introduction and Coverage in the WHO African Region. Vaccines. 2024 Sep 18;12(9):1069. DIDE. 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A Survey of Vaccine-Induced Measles IgG Antibody Titer to Verify Temporal Changes in Response to Measles Vaccination in Young Adults. Vaccines. 2019 Sep 19;7(3):118. Xiong Y, Wang D, Lin W, Tang H, Chen S, Ni J. Age-related changes in serological susceptibility patterns to measles. Hum Vaccines Immunother. 2014 Jan 21;10(4):1097–103. Hachiya M, Vynnycky E, Mori Y, Do HT, Huynh MK, Trinh LH, et al. Inuwa. Int J Infect Dis [Internet]. 2024 Jul 1 [cited 2025 Jul 27];144. Available from: https://www.ijidonline.com/article/S1201-9712(24)00123-1/fulltext Knipes AK, Summers A, Sklavounos AA, Lamanna J, de Campos RPS, Narahari T, et al. Use of a rapid digital microfluidics-powered immunoassay for assessing measles and rubella infection and immunity in outbreak settings in the Democratic Republic of the Congo. PloS One. 2022;17(12):e0278749. Manirakiza A, Kipela JM, Sosler S, Daba RM, Gouandjika-Vasilache I. Seroprevalence of measles and natural rubella antibodies among children in Bangui, Central African Republic. BMC Public Health. 2011 May 17;11(1):327. Castiñeiras ACP, Sales AC, Picone C de M, Diogo CL, Rossi ÁD, Galliez RM, et al. The decline of measles antibody titers in previously vaccinated adults: a cross-sectional analysis. Rev Inst Med Trop São Paulo. 2024 Jan 5;66:e4. Haralambieva IH, Ovsyannikova IG, O’Byrne M, Pankratz VS, Jacobson RM, Poland GA. A large observational study to concurrently assess persistence of measles specific B-cell and T-cell immunity in individuals following two doses of MMR vaccine. Vaccine. 2011 Jun 15;29(27):4485–91. Zibolenová J, Hudečková H, Chladná Z, Malobická E, Novák M, Waczulíková I, et al. Quantification of Waning Immunity After Measles Vaccination—Evidence From a Seroprevalence Study. Am J Epidemiol. 2023 Aug 4;192(8):1379–85. LeBaron CW, Beeler J, Sullivan BJ, Forghani B, Bi D, Beck C, et al. Persistence of measles antibodies after 2 doses of measles vaccine in a postelimination environment. Arch Pediatr Adolesc Med. 2007 Mar;161(3):294–301. Stanescu A, Ruta SM, Leustean M, Iosif I, Sultana C, Panaitescu AM, et al. A Nationwide Seroprevalence Study for Measles in Individuals of Fertile Age in Romania. Antibodies. 2025 Jun;14(2):32. Al-Rawahi B, Patel P, Al-Farsi N, Al-Kindi H, Al-Jardani A, Al-Shukri I, et al. Cross-sectional, laboratory-based study of measles seroprevalence in Oman. 2025;31(01). Saffar H, Khalifeloo M, Saffar MJ, Abdollahi A, Parsaei MR, Ghorbani GR, et al. Measles and rubella serosusceptibity among population vaccinated with different schedules: the potential impact on measles-rubella elimination in Iran. BMC Infect Dis. 2021 Mar 25;21(1):305. Klein SL, Marriott I, Fish EN. Sex-based differences in immune function and responses to vaccination. Trans R Soc Trop Med Hyg. 2015 Jan;109(1):9–15. Gohil DJ, Kothari ST, Chaudhari AB, Gunale BK, Kulkarni PS, Deshmukh RA, et al. Seroprevalence of Measles, Mumps, and Rubella Antibodies in College Students in Mumbai, India. Viral Immunol. 2016 Apr;29(3):159–63. Kumakura S, Shibata H, Onoda K, Nishimura N, Matsuda C, Hirose M. Seroprevalence survey on measles, mumps, rubella and varicella antibodies in healthcare workers in Japan: sex, age, occupational-related differences and vaccine efficacy. Epidemiol Infect. 2014 Jan;142(1):12–9. Domínguez A, Plans P, Costa J, Torner N, Cardenosa N, Batalla J, et al. Seroprevalence of measles, rubella, and mumps antibodies in Catalonia, Spain: results of a cross-sectional study. Eur J Clin Microbiol Infect Dis Off Publ Eur Soc Clin Microbiol. 2006 May;25(5):3107. Mossong J, O’Callaghan CJ, Ratnam S. Modelling antibody response to measles vaccine and subsequent waning of immunity in a low exposure population. Vaccine. 2000 Oct 15;19(4–5):523–9. Vaidya SR, Kumbhar NS, Bhide VS. Detection of measles, mumps and rubella viruses by immuno-colorimetric assay and its application in focus reduction neutralization tests. Microbiol Immunol. 2014 Dec;58(12):666–74. Fatemi Nasab GS, Salimi V, Abbasi S, Adjami Nezhad Fard F, Mokhtari Azad T. Comparison of neutralizing antibody titers against outbreak-associated measles genotypes (D4, H1 and B3) in Iran. Pathog Dis. 2016 Nov;74(8):ftw089. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9210123","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":620351834,"identity":"5de23b60-4f3b-4ed4-a49d-a1cb5c413f9d","order_by":0,"name":"Kalilu S. Donzo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5klEQVRIiWNgGAWjYBACCQYGAxAtBxNgbGBgYCNKizFMHfFaEhuI1iLZf3jj44I/Nunz5zewSX5hsJHdcID92gN8WqQl0oqNZ/Ck5W44xsAmLcOQZrzhAE+5AT4tchI8ZtI8EodzN7ABtUgwHE4EakmTwKuF/wxQi8HhdPk2sJb/hLVIM+QAtSQcTmAAOkzyA8MBoBb2Y3i1SM4A+oXnQJrhhmOJzdYMBsnGMw/zsOHVInEeGGI8f2zk5ZsPH7z5o8JOtu94+zO8WpAAYwMzDyioICSxmn6AKfYHxGsZBaNgFIyCkQAARp5B6eYD4soAAAAASUVORK5CYII=","orcid":"","institution":"University of Ghana","correspondingAuthor":true,"prefix":"","firstName":"Kalilu","middleName":"S.","lastName":"Donzo","suffix":""},{"id":620351835,"identity":"bdc99b63-4252-485f-aa4a-67a19e691ceb","order_by":1,"name":"Nicola Logan","email":"","orcid":"","institution":"MRC University of Glasgow Centre for Virus Research","correspondingAuthor":false,"prefix":"","firstName":"Nicola","middleName":"","lastName":"Logan","suffix":""},{"id":620351836,"identity":"f6e27291-23cc-4070-a4d9-e34cde938cf8","order_by":2,"name":"TROY D. MOON","email":"","orcid":"","institution":"Tulane University","correspondingAuthor":false,"prefix":"","firstName":"TROY","middleName":"D.","lastName":"MOON","suffix":""},{"id":620351837,"identity":"60cc44b1-7684-4a95-adc9-33fa2ff5c8c9","order_by":3,"name":"Ralph W. Jetoh","email":"","orcid":"","institution":"National Public Health Institute of Liberia","correspondingAuthor":false,"prefix":"","firstName":"Ralph","middleName":"W.","lastName":"Jetoh","suffix":""},{"id":620351838,"identity":"a764c4d7-ed01-4f08-b061-4659e69a41c5","order_by":4,"name":"Margaret J. Hosie","email":"","orcid":"","institution":"MRC University of Glasgow Centre for Virus Research","correspondingAuthor":false,"prefix":"","firstName":"Margaret","middleName":"J.","lastName":"Hosie","suffix":""},{"id":620351845,"identity":"9cde862e-3262-4bd4-bb91-49aaa4507e76","order_by":5,"name":"Peter Kojo Quashie","email":"","orcid":"","institution":"University of Ghana","correspondingAuthor":false,"prefix":"","firstName":"Peter","middleName":"Kojo","lastName":"Quashie","suffix":""},{"id":620351848,"identity":"4ba7429e-8ff2-4420-a6bb-aee32e46875e","order_by":6,"name":"Brian J. Willett","email":"","orcid":"","institution":"MRC University of Glasgow Centre for Virus Research","correspondingAuthor":false,"prefix":"","firstName":"Brian","middleName":"J.","lastName":"Willett","suffix":""},{"id":620351849,"identity":"f7c7e9b0-af79-4733-b5d2-21e48d86eb34","order_by":7,"name":"Kwadwo Asamoah Kusi","email":"","orcid":"","institution":"Noguchi Memorial Institute for Medical Research","correspondingAuthor":false,"prefix":"","firstName":"Kwadwo","middleName":"Asamoah","lastName":"Kusi","suffix":""}],"badges":[],"createdAt":"2026-03-24 09:54:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9210123/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9210123/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":106871465,"identity":"aebf624a-3196-429f-bf27-199e22e6d03c","added_by":"auto","created_at":"2026-04-14 09:47:39","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":524975,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparison of measles‑specific IgG seroprevalence.\u003c/strong\u003e (a) overall seroprevalence among study participants, (b) seroprevalence across age groups, (c) seroprevalence by gender, and (d) seroprevalence based on vaccination history. All bar charts were generated using R version 4.3.1.\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9210123/v1/5405b47a809f9c76cecf5a63.jpeg"},{"id":106961377,"identity":"832d92c7-b5dd-406a-9509-4959839f94cf","added_by":"auto","created_at":"2026-04-15 09:25:19","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1139329,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparison between levels of MeV IgG by vaccination status and age group.\u003c/strong\u003e The Wilcoxon signed ranked test was used to compare the median between vaccinated vs unvaccinated and age group. A-B show the concentrations in Uml/ml of IgG antibody between vaccination status and age group. The bold lines reveal median values. A p-value less than 0.05 was deemed statistically significant.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9210123/v1/cf79f0eb83ecdb8198125204.png"},{"id":106871464,"identity":"a94bd90c-3a83-4a0e-82a2-cf415bd48c24","added_by":"auto","created_at":"2026-04-14 09:47:39","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1038319,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of MeV neutralization titers of seropositive individuals against four genotypes. The Kruskal–Wallis test was utilized to compare median values across the four groups. Bold lines denote the medians, and a p-value of less than 0.05 was considered statistically significant. The red dotted lines represent the reference titer defined by the third WHO standard serum (NIBSC 97/648).\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-9210123/v1/8698b925a46e62ca099b7d62.png"},{"id":106871468,"identity":"6c919073-487c-40df-93d0-da425da8684e","added_by":"auto","created_at":"2026-04-14 09:47:39","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":641595,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparison of neutralizing antibodies responses against Edmonston, B3, D4 and D8 by vaccinations status\u003c/strong\u003e. The Wilcoxon signed ranked test was used to compare the median between the two groups. The bold lines reveal median values. p-value \u0026lt;0.05 was considered statistically significant. Statistical significance is indicated as follows: (a) Edmonston (* p-value = 0.0245), (b) B3 (** p-value = 0.0012), (c) D4 (*** p-value = 0.001) and (d) D8 (**** p-value \u0026lt; 0.001).\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-9210123/v1/a3e6f8c1f59c4ee221cbe7b9.png"},{"id":106961237,"identity":"048cf120-e614-450b-9931-2b2244583e40","added_by":"auto","created_at":"2026-04-15 09:24:47","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":425188,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation between neutralization titers (Edmonston, B3, D4, D8) and age. Spearman’s rank correlation rho was used to analyze the associations. p-value \u0026lt;0.05 was considered statistically significant.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-9210123/v1/59be1a47d40d1f6230b20d30.png"},{"id":106961039,"identity":"0d2da256-a8d2-4a64-8aaf-3d18e5c783e9","added_by":"auto","created_at":"2026-04-15 09:24:02","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":473009,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation between measles-specific IgG and neutralization titers against (a)Edmonston (b) B3 (c) D4 (d) D8. Spearman’s rank correlation rho was used to analyze the associations. p-value \u0026lt;0.05 was considered statistically significant.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-9210123/v1/1d7476923227f6dd6a516c51.png"},{"id":108805437,"identity":"8b2ac283-c328-4d0e-b1bd-317254b4f7f3","added_by":"auto","created_at":"2026-05-08 15:25:58","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3350680,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9210123/v1/58f00f51-1e29-42d8-884a-012fa4df7671.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Seroprevalence of measles-specific IgG and genotype-specific neutralizing antibody responses in clinically confirmed cases during the 2021–2023 measles outbreaks in Liberia","fulltext":[{"header":"BACKGROUND","content":"\u003cp\u003eMeasles is a highly contagious airborne viral infection caused by measles virus (MeV) resulting in severe complications and sometime death. These severe complications are predominantly in young children due to immature immunity, waning maternal antibodies, and delayed vaccination (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e). MeV is spread through respiratory droplets, and clinical symptoms typically include high fever, cough, conjunctivitis, and a characteristic maculopapular rash. Measles symptoms typically develop 10\u0026ndash;14 days after exposure to the virus. The World Health Organization (WHO) case definition of measles categorizes a suspected case as a patient having a temperature over 38\u0026deg;C and a maculopapular rash. According to WHO, a clinical case of measles is defined as any patient presenting with a fever, a maculopapular rash, and at least one of the following symptoms: cough, coryza, or conjunctivitis.\u003c/p\u003e \u003cp\u003eDespite the availability of safe and effective vaccines, measles continues to pose a significant global health challenge. In 2023, over 107,500 measles-related mortalities occurred globally, largely among unvaccinated children under five years of age. In 2022, Measles Containing Vaccine dose 1 (MCV1) coverage declined to 83% globally, its lowest since 2008 (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e). In Liberia, MCV1 coverage increased from 58% in 2021 to 82% in 2023, and MCV2 from 50% in 2019 to 60% in 2023 (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e). However, Liberia has experienced a nationwide outbreak since 2021, with 14,192 confirmed cases and 98 deaths reported as of December 14, 2025 (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe B3 genotype remains the predominant endemic measles virus lineage circulating in sub-Saharan Africa, with sustained transmission documented across Western and Central Africa (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e). This genotype has been repeatedly reported in Nigeria, Ghana, Cameroon, and The Gambia, reflecting its long-standing regional establishment (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e). In contrast, the D4 and D8 genotypes show greater genetic heterogeneity and are more often associated with outbreaks and importation events, particularly in eastern and southern parts of the continent (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e). D4 genotypes have been detected in countries such as Uganda, Tanzania, and South Africa, with many reports suggesting importation or short-term regional dissemination rather than persistent endemic circulation (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e). Similarly, D8 genotype viruses have been identified in South Africa and Zimbabwe in recent surveillance years, although their occurrence has varied from year to year, indicating sporadic introductions rather than continuous transmission (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSerological surveillance is crucial for ascertaining immunity gaps and evaluating vaccination program performance. IgG seroprevalence surveys help assess population protection, while neutralization assays are crucial for measuring functional immunity, as Enzyme-Linked Immunosorbent Assay (ELISA) cannot differentiate neutralizing from non-neutralizing antibodies (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e). Neutralizing antibodies targeting MeV hemagglutinin (H) and fusion (F) proteins are key to protection and reflect the antigenic variability of circulating genotypes (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e). Previously, studies have shown genotype-specific differences in neutralizing responses. Lower titers against MeV genotype A compared with D4 and D8, reduced titers against genotype B3 in Iran, and variable responses across genotypes in the United Kingdom (UK) demonstrate the importance of assessing genotype-specific immunity (10\u0026ndash;12, 34).\u003c/p\u003e \u003cp\u003eLiberia introduced MCV1 in 1978 and MCV2 in 2019, but there is no data on measles IgG seroprevalence, vaccine-induced immunity, or genotype-specific neutralization. This study aimed to assess MeV-specific IgG seroprevalence in clinically confirmed measles patients and to evaluate the neutralization breadth of MeV-specific IgG against four genotypes during Liberia\u0026rsquo;s ongoing outbreak.\u003c/p\u003e"},{"header":"METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy Design and Subject Selection Criteria\u003c/h2\u003e \u003cp\u003eThe study employed a cross-sectional design that consisted of two components: a retrospective evaluation using whole-blood samples obtained from individuals meeting the suspected case definition for MeV stored at the National Reference Laboratory of Liberia from December 2021 to August 2023 and a prospective study that collected samples from March 2023 to June 2023 of clinically diagnosed MeV patients at the Redemption Hospital in Monrovia, Liberia.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSeparation of Plasma and Sera from Whole Blood.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eWe collected whole blood using BD Vacutainer\u0026reg; cell preparation tubes, centrifuged for 30 minutes at 1800 x g at room temperature. Plasma was then transferred into 2 mL tubes and stored at \u0026minus;\u0026thinsp;80\u0026deg;C.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eEnzyme-Linked Immunosorbent Assay (ELISA)\u003c/h3\u003e\n\u003cp\u003eAll samples were brought to 25\u0026deg;C, and MeV-specific IgG was quantified using a commercial ELISA kit (SERION ELISA classic measles virus IgG) according to the manufacturer\u0026rsquo;s instructions. The commercial ELISA kit uses recombinant MeV nucleoprotein derived from the Edmonston strain. Samples were diluted 1:100 (5 \u0026micro;L sample\u0026thinsp;+\u0026thinsp;495 \u0026micro;L diluent), loaded with controls onto 96-well plates, and the plates were incubated for 60 minutes at 37\u0026deg;C. After the washing steps, plates were incubated for 30 minutes with anti-human IgG conjugate at 37\u0026deg;C and washed again. The substrate solution containing para-nitrophenylphosphate was added and incubated for 30 minutes at 37\u0026deg;C. The reaction was stopped using 1.2 N NaOH, and optical density was measured at 405 nm. Antibody titers (mIU/mL) were calculated using the manufacturer\u0026rsquo;s calibration specifications, with serostatus defined as \u0026lt;\u0026thinsp;150 (negative), 150\u0026ndash;200 (equivocal), and \u0026gt;\u0026thinsp;200 (positive). A positive IgG result indicated prior infection or vaccination.\u003c/p\u003e\n\u003ch3\u003eCell Lines and Viruses\u003c/h3\u003e\n\u003cp\u003eHuman embryonic kidney (HEK) 293T cells were cultured and engineered to express the human SLAM1 receptor under standard culture conditions as described by Logan et al. SLAM1 (CD150), expressed on immune cells, is the primary receptor for wild-type MeV. Cells were cultured and maintained in DMEM supplemented with 10% FBS, 100 IU/mL penicillin-streptomycin, and 2 mM L-glutamine. For stable selection, HEK 293 SLAM1 cells were grown in medium containing 1 \u0026micro;g/mL puromycin and HEK 293T cells with 400 \u0026micro;g/mL G418. These conditions ensured consistent SLAM1 expression and reliable experimental performance. All reagents were provided by Hosie\u0026rsquo;s and Willett\u0026rsquo;s laboratories at the Centre for Virus Research, University of Glasgow.\u003c/p\u003e\n\u003ch3\u003eProduction of Vesicular Stomatitis Virus ΔG (VSV ΔG) MeV Pseudovirus\u003c/h3\u003e\n\u003cp\u003eThe VSV ΔG\u0026ndash;MeV pseudoviruses were generated using four MeV genotypes (Edmonston, B3, D8, and D4). Plasmid vectors encoding each genotype\u0026rsquo;s H and F glycoproteins were synthesized, and pseudoviruses were produced by transfecting 2 \u0026times; 10⁶ HEK 293T cells with 5 \u0026micro;g each of H and F plasmids. After 4 hours, cells were infected with VSV ΔG Luc (1.15 \u0026times; 10⁷ TCID₅₀; MOI 0.02) for 1 hour, then washed and incubated in 10 mL DMEM for 48 hours at 37\u0026deg;C/5% CO₂. Supernatants were then filtered through a 0.45 \u0026micro;m filter, and viral titers were determined by TCID₅₀ on HEK 293 SLAM1 cells.\u003c/p\u003e\n\u003ch3\u003ePseudotype-Based Neutralization Assay\u003c/h3\u003e\n\u003cp\u003eThe retrospective and prospective serum samples were serially diluted 4‑fold from 1:16 to 1:32,768, and the diluted sera were incubated in triplicate with 2.5 \u0026times; 10\u0026sup3; TCID₅₀ of pseudotyped virus in 96‑well plates for 1 hour at 37\u0026deg;C/5% CO₂. Afterward, 2 \u0026times; 10⁴ HEK 293 SLAM1 cells were added and incubated on plates for 48 hour before adding Steadylite Plus\u0026trade; luciferase substrate and measuring luminescence on a Revvity EnSight\u0026reg; plate reader.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eData and Statistical Analysis\u003c/h2\u003e \u003cp\u003eAll data were analysed using GraphPad Prism 7.01 (GraphPad Software, San Diego, CA, USA)\u003c/p\u003e \u003cp\u003eand R 4.3.1 (R Development Core Team, including ggplot2 for visualization). MeV‑specific IgG levels were compared between vaccinated and unvaccinated groups using the two‑tailed Mann\u0026ndash;Whitney U test. Neutralizing antibody responses to the three wild-type genotypes (B3, D4, and D8) were evaluated in comparison with the vaccine genotype, Edmonston. A WHO reference serum product number NIBSC code 97/648 (3000 mIU/mL; protective level 125 mIU/mL) was diluted and included to define the protective threshold\u0026mdash;the minimum measles-specific antibody level that confers protective immunity\u0026mdash;in the pseudotype assay. Median neutralizing titers across genotypes were compared using the Kruskal\u0026ndash;Wallis test and vaccinated versus unvaccinated titers were analyzed using the Wilcoxon matched‑pairs signed rank test. Spearman's rank correlation was used to assess the relationships between IgG status and age, as well as the associations between Edmonston, B3, D4, and D8 neutralization titers and age. Statistical significance was set at p-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e"},{"header":"RESULTS","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eDemographics Characteristics\u003c/h2\u003e \u003cp\u003eA total of one hundred and ninety-nine (199) samples were analysed for MeV-specific IgG (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Participant characteristics varied by vaccination status. Sex distribution did not differ significantly between groups (p-value\u0026thinsp;=\u0026thinsp;0.50). There were statistically significant differences in age groups (p-value\u0026thinsp;\u0026lt;\u0026thinsp;0.001): vaccinated participants were mainly 11\u0026ndash;20 years old, while unvaccinated participants were also concentrated in this age range, and those with unknown status were mostly younger (\u0026lt;\u0026thinsp;5 years and 5\u0026ndash;10 years). Sample type exhibited statistically significant differences (p-value\u0026thinsp;\u0026lt;\u0026thinsp;0.001), with all unvaccinated participants drawn from prospective samples and all with unknown status from retrospective samples. Clinical presentations were similar, as all participants reported fever and maculopapular rash, with no differences between groups (fever: p-value\u0026thinsp;=\u0026thinsp;1.0; rash: p-value\u0026thinsp;=\u0026thinsp;1.0).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDemographic, and clinical characteristics of participants.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e*Characteristics*\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVaccinated \u003c/p\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;100\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eUnvaccinated \u003c/p\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;17\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eUnknown \u003c/p\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;82\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ep-value\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e199\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFemale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e62 (62.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8 (47.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e48 (58.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e38 (38.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e9 (52.9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e34 (41.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge Group\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e199\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;5 yrs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8 (8.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4 (23.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e34 (41.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u0026ndash;10 yrs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e21 (21.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2 (11.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e23 (28.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11\u0026ndash;20 yrs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e34 (34.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8 (47.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15 (18.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e21\u0026ndash;30 yrs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19 (19.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3 (17.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7 (8.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e31\u0026ndash;56 yrs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18 (18.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0 (0.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3 (3.7%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample Type\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e199\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProspective\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e86 (86.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e17 (100.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0 (0.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRetrospective\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14 (14.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0 (0.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e82 (100.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFever\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e199\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100 (100.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e17 (100.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e82 (100.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaculopapular Rash\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e199\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100 (100.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e17 (100.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e82 (100.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCough\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e199\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.11\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e97 (97.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e17 (100.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e74 (90.2%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3 (3.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0 (0.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8 (9.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eConjunctivitis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e199\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e37 (37.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3 (17.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e33 (40.2%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e63 (63.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14 (82.4%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e49 (59.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003e\u003csup\u003e1\u003c/sup\u003en (%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003e\u003csup\u003e2\u003c/sup\u003ePearson's Chi-squared test; Fisher's exact test\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eSeroprevalence of Measles-Specific IgG\u003c/h2\u003e \u003cp\u003eOut of 199 samples tested for MeV-specific IgG, 139 participants (69.9%) were IgG seropositive, with smaller proportions being seronegative (23.1%) or equivocal (7.0%) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). The IgG status among participants varied by age group. Seronegativity was highest among children\u0026thinsp;\u0026lt;\u0026thinsp;5 years of age (39.1%) with 19.4% being seropositive and 7.1% being equivocal. In the 5\u0026ndash;10-year age group, seronegativity remained common (19.6%), while seropositivity increased to 23% and 37.5% were equivocal. Adolescents aged 11\u0026ndash;20 years recorded the highest proportion of seropositive samples (27.3%), with 26.1% being seronegative, and 50% equivocal. Older adults aged 21\u0026ndash;30 years showed lower seropositivity (16.6%) and no equivocal results, whereas those aged 31\u0026ndash;56 years of age displayed a modest increase in seropositivity (13.7%) alongside low levels of seronegativity and equivocal findings (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). Gender differences were observed in seroprevalence of IgG (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). Female participants exhibited a higher proportion of seropositivity (43.2%) compared with male participants (26.6%), while sero-negativity and equivocal proportions were broadly similar between genders (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). Vaccination status was strongly correlated with being IgG seropositive (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). Vaccinees had the highest rate of seropositivity (52.5%) while unvaccinated participants demonstrated a decreased seropositivity rate (8.6%) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed).\u003c/p\u003e \u003cp\u003eMeV-specific IgG concentration levels did not differ significantly between vaccinated and unvaccinated individuals (p\u0026thinsp;=\u0026thinsp;0.21; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Similarly, no statistically significant differences in MeV-specific IgG levels were observed across age groups (\u0026gt;\u0026thinsp;5 years, 5\u0026ndash;10 years, 11\u0026ndash;20 years, 21\u0026ndash;30 years, and 31\u0026ndash;56 years; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). Although not statistically significant, there was a modest trend toward higher seropositivity with increasing age and vaccination status.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eNeutralizing Antibody Responses to Four MeV genotypes in Seropositive Individuals\u003c/h2\u003e \u003cp\u003eThe percentage of seropositive individuals with neutralizing antibody titers was determined for the four genotypes; our results revealed that 94.7% of seropositive individuals tested demonstrated neutralization titers against Edmonston, 91.6% against B3, 94.7% against D4, and 98.9% against D8 (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Also, we compared MeV-neutralizing antibody titres between three wild-type genotypes (B3, D4, and D8) and vaccine genotype, Edmonston. Our findings revealed that B3 and D8 have significantly higher titers than Edmonston, while D4 has the lowest median neutralizing titer, with more participants below the protective threshold (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe percentage of seropositive individuals with neutralizing titers exceeding the protective threshold.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGenotype\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePercentage Protected (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEdmonston\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e94.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eB3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e91.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eD4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e94.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eD8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e98.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eComparison of MeV neutralization titers with vaccination status\u003c/h2\u003e \u003cp\u003eFor all MeV genotypes assessed, vaccinated individuals displayed higher neutralization titers compared with the unvaccinated participants. This trend was the same for vaccine strain (Edmonston) as well as circulating wild-type B3, D4, and D8 genotypes tested (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea-d).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003eCorrelation between Age and measles-specific IgG on Neutralizing Antibody Titers\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eNeutralization titers against the Edmonston genotype showed a weak but statistically significant positive correlation with increasing age (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). Similarly, neutralization titers against the B3 and D4 genotypes showed a weakly positive correlation with increasing age, though neither was statistically significant (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). Since not all IgG antibodies neutralize, and low IgG still corresponds to neutralizing activity, we subsequently assessed the correlation between measles-specific IgG concentrations and neutralization titers. There was a moderate positive correlation between neutralization titers against D4, Edmonston, and measles IgG antibodies that was strongly statistically significant (Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). The correlation between neutralization titers against D8, B3, and measles IgG antibodies ranged from moderate to strong and weak to moderate positive correlation, respectively (Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eSeroprevalence studies offer critical understanding of the transmission patterns and population-level impact of infectious diseases. By measuring pathogen-specific antibodies, they can help in identifying previous exposure, estimate progress toward herd immunity thresholds, and guide public health interventions. Neutralizing antibody titers, in particular, are widely considered robust correlates of protective immunity, with higher titers generally associated with reduced risks of reinfection and severe disease. Although genotypes responsible for the current outbreak have not been identified, B3 was believed to be circulating in the West African region, including Liberia, in 2010 (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePrevious studies have shown substantial differences in the seroprevalence of measles IgG in different settings. Zahoor et al. (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e) and Adekola et al. (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e) reported seroprevalence around 73.48% and 29.2% while Inuwa et al. (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e) and Smetana et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e) found levels of seroprevalence of 61.6% and 70%. In contrast, significantly higher seroprevalences of measles IgG, ranging from 92% to 99%, were reported in the DRC (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e), other African settings (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e), China (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e) and Vietnam (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e). These variances likely reflect differences in national vaccination efficacy, historical patterns of measles transmission, and the role of natural infection in population immunity (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e). The present study found an overall seroprevalence of 69.9%, with a seropositivity rate of just 52.5% among vaccinated individuals, suggesting immunity gaps in Liberia. The relatively low coverage of MCV1 and particularly MCV2 in Liberia could be contributing to these gaps, underscoring the need for strengthened routine vaccination and targeted strategies. Further study is necessary to understand the underlying factors contributing to low immunity, despite an MCV1 coverage of roughly 82%.\u003c/p\u003e \u003cp\u003eNaturally acquired immunity also affects seroprevalence patterns. In some regions, unvaccinated individuals, especially those aged 30 and above, have seroprevalence that sometimes exceeds 95%, mostly attributable to past encounters with MeV (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e). However, some studies like Manirakiza et al. (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e) showed a decline in measles immunity among specific populations despite vaccination programs, highlighting continued susceptibility in some demographic groups. In contrast to these studies, the present study found significant age-related differences in seropositivity with decreased immunity in children under 5, young adults (21\u0026ndash;30 years), and adults (31\u0026ndash;56 years). Decreased seropositivity in young infants may indicate limited vaccination coverage or waning of maternal antibodies. Stronger or higher titers among school-aged children and teenagers suggest stronger vaccine-derived protection in these demographics as compared to younger children and adults. Together, these findings highlight a changing landscape of susceptibility to measles, with increasing vulnerability in infants and older adults. Age-specific differences influence epidemic risk, especially in areas with low vaccination rates or late second-dose administration. Enhancing regular vaccination, improving maternal immunity, and bolstering catch-up campaigns for adolescents and young adults may be critical for attaining and maintaining measles eradication goals.\u003c/p\u003e \u003cp\u003eEarlier studies have consistently demonstrated waning neutralizing antibodies post-MMR vaccination, prompting concerns over long-term protection. An observational study of adolescents and young adults found that only 23.2% of individuals vaccinated with two doses of MMR maintained antibody levels above the protective threshold 7.4 years later, compared to 8.6% seropositivity among unvaccinated individuals (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e). Modelling-based analyses have indicated annual declines of 9.7% in neutralizing antibodies following the first dosage of MMR and 4.8% after the second dose of MMR (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e). Data from the United States similarly found a seronegativity rate of 33% two decades after MMR vaccination (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e). These findings are consistent with the present study\u0026rsquo;s findings and collectively highlight an increasing risk among vaccinated populations and indicate a necessity to more accurately identify individuals who have titers below protective levels. The declines in neutralizing titers observed in earlier studies align with the present study\u0026rsquo;s finding. Decreased protective titers seen in individuals may suggest limited exposure or suboptimal immune responses to past vaccinations (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e). These data collectively emphasize the need for enhanced monitoring of post-vaccination immunity and more study to elucidate the drivers and clinical consequences of declining measles antibodies.\u003c/p\u003e \u003cp\u003eSero-epidemiological studies have also indicated considerable geographical variation in measles susceptibility. For example, a serosurvey in Romania has revealed a measles seronegativity of 23% (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e), while a cross-sectional survey in Oman identified an even greater susceptibility among individuals aged 15\u0026ndash;20 years (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e). In contrast, lower seronegativity (12.3%) among vaccinees has been reported in Iran (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e). Ristić et al. has also found a susceptibility threshold above WHO\u0026rsquo;s recommended susceptibility threshold of \u0026le;\u0026thinsp;5%. In the Central African Republic, only 51.3% and 27.6% had detectable measles IgG among vaccinees and unvaccinated individuals, respectively (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e). The seronegativity rate of 23.12% found in the present study among participants aligns with these data, suggesting that approximately 1 in 4 participants lacked protective antibodies. Particularly concerning was the low seropositivity (52.5%) among vaccinated participants, despite Liberia\u0026rsquo;s reported MCV1 coverage of approximately 82%.\u003c/p\u003e \u003cp\u003eSex-related differences in vaccine-induced immune responses have been reported. Females tend to generate larger measles-specific antibody titers post-vaccination, whereas males may have a more rapid reduction in these titers (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e). Evidence from various settings corroborates these trends. For instance, studies from India (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e), Europe (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e) and the US (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e) agreed with these trends. The present study found higher seropositivity among females (43.2%) than males (26.5%) consistent with this pattern. Additionally, across-sectional study of children above 15 years who received the MMR vaccine at 12\u0026ndash;15 months indicated significantly higher prevalence of measles-specific IgG antibodies in females than in males (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e). A regression analyses identified age at vaccination and female sex as the two principal determinants of long-term antibody persistence following MMR vaccination (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e). These demographic differences are epidemiologically crucial for maintaining long-term protection against measles. The lower seropositivity seen in men may result in small yet epidemiologically important zones of susceptibility that might facilitate continued viral transmission. The high transmissibility of measles exacerbates the risk of outbreaks due to immunization gaps. To maintain herd immunity and avert a recurrence of measles, it is imperative to implement improved monitoring of male immunity and to conduct targeted vaccinations as necessary.\u003c/p\u003e \u003cp\u003eThis study showed that participants mounted strong neutralizing responses against all four tested MeV genotypes. Titers were significantly higher for B3 as compared to Edmonston, suggesting that wild-type viruses may elicit more robust humoral responses than the attenuated vaccine lineage. Genotype D8 also produced higher titers than D4, indicating genotype-specific differences despite overall antigenic conservation. These findings align with reports of broad cross-neutralization among Edmonston, D4, and D8 (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e), though variability has been noted, such as lower B3 titers in vaccinated individuals in Iran compared with H1, D4, and A genotypes (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e). Further work is needed to understand molecular and structural drivers underlying the stronger responses observed for B3 and D8.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe findings demonstrate strong genotype\u0026ndash;cross neutralizing immunity among vaccinated and seropositive patients, highlighting the critical role of measles vaccination in maintaining effective antibody protection. However, the higher titers against wild-type strains compared to the vaccine strain raises concerns regarding the long-term durability of vaccine-induced immunity. The significant percentage of seronegative patients in our study indicates ongoing vulnerability to measles transmission and reinforces the need to improve vaccination coverage.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eDRC: Democratic Republic of Congo\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDMEM: Dulbecco’s Modified Eagle Medium\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eEIA: Enzyme Immuno-assay\u003c/p\u003e\n\u003cp\u003eELISA: Enzyme-Linked Immuno Assay\u003c/p\u003e\n\u003cp\u003eFBS: Fetal Bovine Serum\u003c/p\u003e\n\u003cp\u003eHEK: Human embryonic kidney\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHRP: Horseradish peroxidase\u003c/p\u003e\n\u003cp\u003eIgG: Immunoglobulin G\u003c/p\u003e\n\u003cp\u003eIgM: Immunoglobulin M\u003c/p\u003e\n\u003cp\u003eIRB: Institutional Review Board\u003c/p\u003e\n\u003cp\u003eMCV: Measles Containing Vaccine\u003c/p\u003e\n\u003cp\u003eMCV1: Measles Containing Vaccine 1\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMCV2: Measles Containing Vaccine 2\u003c/p\u003e\n\u003cp\u003eMeV: Measles Virus\u003c/p\u003e\n\u003cp\u003eMOI : Multiplicity of Infection\u003c/p\u003e\n\u003cp\u003eMRC: Medical Research Council\u003c/p\u003e\n\u003cp\u003eNPHIL: National Public Health Institute of Liberia\u003c/p\u003e\n\u003cp\u003eNPHRL: National Public Health Reference Laboratory\u003c/p\u003e\n\u003cp\u003eOD: Optic density\u003c/p\u003e\n\u003cp\u003ePNA: Pseudovirus Neutralization Assay\u003c/p\u003e\n\u003cp\u003ePREVSL: Partnership for Research in Emerging Viral Infections Sierra Leone\u003c/p\u003e\n\u003cp\u003ePRNT: Plaque Reduction Neutralization Test\u003c/p\u003e\n\u003cp\u003eSLAM: Signaling Lymphocytic Activation Molecule\u003c/p\u003e\n\u003cp\u003eUK: United Kingdom\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eVSVΔG: Vesicular Stomatitis Virus Delta G\u003c/p\u003e\n\u003cp\u003eWACCBIP: West African Centre for Cell Biology of Infectious Pathogens\u003c/p\u003e\n\u003cp\u003eWHO: World Health Organization\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was funded in part by Science for Africa Foundation to the Developing Excellence in Leadership, Training and Science in Africa (DELTAS Africa) programme [DEL-22-014] with support from Wellcome and the UK Foreign, Commonwealth \u0026amp; Development Office and is part of the EDCPT2 programme supported by the European Union. This work was also supported by a fellowship to KSD from a World Bank African Centres of Excellence grant (WACCBIP+NCDs: Awandare). \u0026nbsp;In addition, research reported in this publication was supported by the Fogarty International Center of the National Institutes of Health under Award Number U2RTW011248. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Funders. For purposes of open access, the author has applied a CC BY public copyright licence to any Author Accepted Manuscript version arising from this submission.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAll data supporting this study conclusion are all included within the article. Additional datasets are available from the corresponding author upon request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supervised by Prof. Kwadwo Asamoah Kusi, Prof. Peter Kojo Quashie, NMIMR, and WACCBIP, Prof. Troy D. Moon, Department of Tropical Medicine and Infectious Diseases, Tulane University, Prof. Margaret J. Hosie, Prof. Brian J. Willett, and Nicola Logan from the and MRC–University of Glasgow Centre for Virus Research, and\u0026nbsp;Dr. Ralph W. Jetoh\u0026nbsp;fromNational Public Health Institute of Liberia, Oldest Congo Town, Monrovia, Liberia.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eI am grateful to NPHIL for providing all the retrospective samples and all the participants and their families who participated in this study for their time, cooperation, and trust. I am also grateful to the management and staff of Redemption Hospital for their assistance in collecting the prospective samples at the hospital. I wish to express my sincere appreciation to Prof. Margaret J. Hosie, Prof. Brian J. Willett, Nicola Logan, and all members of the Hosie Laboratory at the MRC–University of Glasgow Centre for Virus Research for their generous guidance, assistance, and support throughout my stay.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors and Affiliations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eWest African Centre for Cell Biology of Infectious Pathogens, University of Ghana, Legon-Accra, Ghana\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eKalilu S Donzo and Prof. Peter Kojo Quashie\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eDepartment of Biochemistry, Cell, and Molecular Biology, University of Ghana, Legon-Accra, Ghana\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eKalilu S Donzo\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eImmunology Department, Noguchi Memorial Institute of Medical Research, College of Health Sciences, University of Ghana, Accra, Ghana\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eProf. Kwadwo Asamoah Kusi\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eMRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eProf. Margaret J. Hosie, Prof. Brian J. Willett, and Nicola Logan\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eTulane University School of Public Health and Tropical Medicine, New Orleans, Louisiana\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eProf. Troy D. Moon\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eNational Public Health Institute of Liberia, Oldest Congo Town, Monrovia, Liberia\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eDr. Ralph W. Jetoh\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eContributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eKAK, PKQ, and K.S.D. contributed to the design and conceptualization of the study; K.S.D. and R.W.J. contributed to sample collection and processing. K.S.D. performed the ELISA and data analysis and drafted the manuscript. K.S.D. and N.L. performed and assisted with the PNA assay, and B.J.W. and M.J.H. assisted with PNA data analysis. K.A.K., PKQ, T.D.M., M.J.H., B.J.W., and N.L. provided resources and contributed to data interpretation, writing, review, and editing of the manuscript. All authors read and approved the final version.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorresponding authors\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorrespondence to Kwadwo Asamoah Kusi and Kalilu S. Donzo\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study received ethical approval from the University of Liberia Institutional Review Board (ULIRBIORG-IRB Number: IRB00013730) and the Noguchi Memorial Institute for Medical Research Institutional Review Board (NMIMR-IRB 0000908). All identifying details, including names and addresses, were removed before data analysis to ensure confidentiality. The collected data was then stored in a secure folder. The study was conducted in accordance with the ethical principles of the Declaration of Helsinki. Written informed consent and assent were obtained from the parents or legal guardians of all participating children.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors have reviewed and approved the final version of this manuscript. We confirm that every author has agreed to its submission and consents to its publication.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eCDC. Measles (Rubeola). 2025 [cited 2025 Mar 8]. Clinical Overview of Measles. Available from: https://www.cdc.gov/measles/hcp/clinical-overview/index.html\u003c/li\u003e\n\u003cli\u003eWHO. 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Vaccines. 2019 Sep 19;7(3):118. \u003c/li\u003e\n\u003cli\u003eXiong Y, Wang D, Lin W, Tang H, Chen S, Ni J. Age-related changes in serological susceptibility patterns to measles. Hum Vaccines Immunother. 2014 Jan 21;10(4):1097\u0026ndash;103. \u003c/li\u003e\n\u003cli\u003eHachiya M, Vynnycky E, Mori Y, Do HT, Huynh MK, Trinh LH, et al. Inuwa. Int J Infect Dis [Internet]. 2024 Jul 1 [cited 2025 Jul 27];144. Available from: https://www.ijidonline.com/article/S1201-9712(24)00123-1/fulltext\u003c/li\u003e\n\u003cli\u003eKnipes AK, Summers A, Sklavounos AA, Lamanna J, de Campos RPS, Narahari T, et al. Use of a rapid digital microfluidics-powered immunoassay for assessing measles and rubella infection and immunity in outbreak settings in the Democratic Republic of the Congo. PloS One. 2022;17(12):e0278749. \u003c/li\u003e\n\u003cli\u003eManirakiza A, Kipela JM, Sosler S, Daba RM, Gouandjika-Vasilache I. 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Quantification of Waning Immunity After Measles Vaccination\u0026mdash;Evidence From a Seroprevalence Study. Am J Epidemiol. 2023 Aug 4;192(8):1379\u0026ndash;85. \u003c/li\u003e\n\u003cli\u003eLeBaron CW, Beeler J, Sullivan BJ, Forghani B, Bi D, Beck C, et al. Persistence of measles antibodies after 2 doses of measles vaccine in a postelimination environment. Arch Pediatr Adolesc Med. 2007 Mar;161(3):294\u0026ndash;301. \u003c/li\u003e\n\u003cli\u003eStanescu A, Ruta SM, Leustean M, Iosif I, Sultana C, Panaitescu AM, et al. A Nationwide Seroprevalence Study for Measles in Individuals of Fertile Age in Romania. Antibodies. 2025 Jun;14(2):32. \u003c/li\u003e\n\u003cli\u003eAl-Rawahi B, Patel P, Al-Farsi N, Al-Kindi H, Al-Jardani A, Al-Shukri I, et al. Cross-sectional, laboratory-based study of measles seroprevalence in Oman. 2025;31(01). \u003c/li\u003e\n\u003cli\u003eSaffar H, Khalifeloo M, Saffar MJ, Abdollahi A, Parsaei MR, Ghorbani GR, et al. Measles and rubella serosusceptibity among population vaccinated with different schedules: the potential impact on measles-rubella elimination in Iran. BMC Infect Dis. 2021 Mar 25;21(1):305. \u003c/li\u003e\n\u003cli\u003eKlein SL, Marriott I, Fish EN. Sex-based differences in immune function and responses to vaccination. Trans R Soc Trop Med Hyg. 2015 Jan;109(1):9\u0026ndash;15. \u003c/li\u003e\n\u003cli\u003eGohil DJ, Kothari ST, Chaudhari AB, Gunale BK, Kulkarni PS, Deshmukh RA, et al. Seroprevalence of Measles, Mumps, and Rubella Antibodies in College Students in Mumbai, India. Viral Immunol. 2016 Apr;29(3):159\u0026ndash;63. \u003c/li\u003e\n\u003cli\u003eKumakura S, Shibata H, Onoda K, Nishimura N, Matsuda C, Hirose M. Seroprevalence survey on measles, mumps, rubella and varicella antibodies in healthcare workers in Japan: sex, age, occupational-related differences and vaccine efficacy. Epidemiol Infect. 2014 Jan;142(1):12\u0026ndash;9. \u003c/li\u003e\n\u003cli\u003eDom\u0026iacute;nguez A, Plans P, Costa J, Torner N, Cardenosa N, Batalla J, et al. Seroprevalence of measles, rubella, and mumps antibodies in Catalonia, Spain: results of a cross-sectional study. Eur J Clin Microbiol Infect Dis Off Publ Eur Soc Clin Microbiol. 2006 May;25(5):3107. \u003c/li\u003e\n\u003cli\u003eMossong J, O\u0026rsquo;Callaghan CJ, Ratnam S. Modelling antibody response to measles vaccine and subsequent waning of immunity in a low exposure population. Vaccine. 2000 Oct 15;19(4\u0026ndash;5):523\u0026ndash;9. \u003c/li\u003e\n\u003cli\u003eVaidya SR, Kumbhar NS, Bhide VS. Detection of measles, mumps and rubella viruses by immuno-colorimetric assay and its application in focus reduction neutralization tests. Microbiol Immunol. 2014 Dec;58(12):666\u0026ndash;74. \u003c/li\u003e\n\u003cli\u003eFatemi Nasab GS, Salimi V, Abbasi S, Adjami Nezhad Fard F, Mokhtari Azad T. Comparison of neutralizing antibody titers against outbreak-associated measles genotypes (D4, H1 and B3) in Iran. Pathog Dis. 2016 Nov;74(8):ftw089. \u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Measles virus outbreak, MeV-specific IgG, neutralizing antibody, clinically-confirmed cases, seroprevalence, Liberia, neutralization breadth, measles containing vaccine, genotype–cross-neutralizing","lastPublishedDoi":"10.21203/rs.3.rs-9210123/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9210123/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eSince 2021, Liberia has experienced disruptive outbreaks of measles across all of its 15 counties, despite the availability of a safe, effective vaccine. There is no data on the potential role of vaccine-induced immunity and no study on seroprevalence of measles-specific IgG in Liberia. Furthermore, there is no data on genotype-specific variation in antibody effectiveness in Liberia. This study evaluated the seroprevalence of measles virus (MeV)-specific IgG in clinically diagnosed patients in Liberia and assessed the breadth of neutralization against four genotypes.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eSamples collected retrospectively from 2021 to 2023 and prospective samples collected in 2023 from clinically diagnosed measles cases were analyzed in this study. Study participants included both vaccinated and unvaccinated individuals. MeV-specific IgG antibody was assessed using an enzyme-linked immunosorbent assay. Neutralizing antibodies against the Edmonston, B3, D4, and D8 MeV genotypes were measured using vesicular stomatitis virus pseudotype-based neutralization assays.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eOverall, 69.9% of 199 individuals, including 100 vaccinees that were clinically diagnosed with measles, tested positive for MeV-specific IgG antibodies. MeV-specific IgG positivity was higher in vaccinated (52.5%) than in unvaccinated individuals (8.6%). Strong neutralization was observed against the D8 genotype in 98.9% of seropositive individuals, compared to 94.7% against Edmonston and D4 genotypes and 91.6% against B3. Significantly higher neutralization titers were observed in vaccinated compared to unvaccinated individuals for all four genotypes (p\u0026thinsp;\u0026lt;\u0026thinsp;0.0001). There was a weak positive correlation between IgG levels, neutralizing titers, and participant age.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eThe findings demonstrate strong genotype-cross-neutralizing immunity among vaccinated and seropositive patients, highlighting the critical role of measles vaccination in maintaining effective antibody protection. The significant percentage of seronegative patients indicates ongoing vulnerability to measles transmission and reinforces the need to improve vaccination coverage.\u003c/p\u003e","manuscriptTitle":"Seroprevalence of measles-specific IgG and genotype-specific neutralizing antibody responses in clinically confirmed cases during the 2021–2023 measles outbreaks in Liberia","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-14 09:47:32","doi":"10.21203/rs.3.rs-9210123/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"51581822-a9ca-4d52-a143-7a1c3f104130","owner":[],"postedDate":"April 14th, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Rejected","date":"2026-05-07T08:00:33+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-05T17:44:05+00:00","index":41,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-29T10:50:49+00:00","index":40,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-05-07T08:13:18+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-14 09:47:32","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9210123","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9210123","identity":"rs-9210123","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}