Progress and gaps in poliovirus immunity: Evidence from a serological survey of children aged 6-23 months in high-risk districts of Pakistan

Progress and gaps in poliovirus immunity: Evidence from a serological survey of children aged 6-23 months in high-risk districts of Pakistan | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Progress and gaps in poliovirus immunity: Evidence from a serological survey of children aged 6-23 months in high-risk districts of Pakistan Imtiaz Hussain, Ahmad Khan, Muhammad Umer, Muhammad Sajid, Haider Abbass, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7664228/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 30 Dec, 2025 Read the published version in npj Vaccines → Version 1 posted 12 You are reading this latest preprint version Abstract Wild poliovirus remains endemic in Pakistan and Afghanistan despite global progress. We quantified immunity to poliovirus types 1–3 among children aged 6–23 months in 44 high-risk districts (2022–2023) using a cross-sectional serosurvey with PPS cluster sampling. We enrolled 20,680 children (10,112 aged 6–11 months; 10,568 aged 12–23 months). Seroprevalence among 6–11-month-olds was 94.5% (type 1), 44.6% (type 2), and 88.0% (type 3); among 12–23-month-olds. It was 95.9%, 53.8%, and 91.2%, respectively. Type 1 seropositivity was highest across provinces; type 3 exceeded 90% except in Balochistan and KP; type 2 was lowest everywhere. Younger children have lower immunity. In multivariable models, residence in Balochistan predicted reduced seroprotection (AOR 0.178, 95% CI 0.066–0.484); older age (AOR 1.356, 1.161–1.583) and full immunization (AOR 2.004, 1.643–2.444) increased odds; <4 OPV doses showed higher odds (AOR 1.25, 1.021–1.529). Wealth showed a non-linear association. Gaps in types 2–3 warrant stronger RI, expanded IPV, and tailored SIAs. Health sciences/Diseases Health sciences/Health care Biological sciences/Immunology Health sciences/Medical research Biological sciences/Microbiology Poliovirus seroprevalence children aged 6–23 months immunity gaps polio high-risk districts Pakistan Figures Figure 1 Figure 2 Introduction Poliomyelitis remains a significant public health concern despite remarkable progress towards its global eradication. Caused by the poliovirus, an enterovirus mainly spread through the fecal-oral route, it can result in permanent paralysis and, in severe cases, death [ 1 ]. Following the launch of the Global Polio Eradication Initiative (GPEI) in 1988, there has been a decrease of more than 99% in the global incidence of polio. However, Pakistan and Afghanistan continue to be among the last two countries where the wild poliovirus (WPV) is still being transmitted [ 2 , 3 ]. In Pakistan, WPV cases have been continuously reported over the years. In 2022, 20 WPV cases were reported in the country, followed by 6 cases in 2023, 74 cases in 2024, and 24 cases as of September 2025 [ 4 ]. Sustained progress towards polio eradication has fundamentally reshaped population immunity profiles, yet pockets of susceptibility persist where routine immunization and supplementary campaigns have been unevenly disturbed [ 5 – 7 ]. Serological surveys provide programmatically actionable estimates of functional protection as they measure neutralizing antibodies directly, revealing gaps that administrative coverage of campaign tallies may miss [ 8 – 10 ]. Evidence from globally diverse settings, including China, Germany, the United States, the Democratic Republic of Congo (DRC), Nigeria, and Cameroon, consistently shows subnational and age-specific variation in seropositivity for poliovirus with implications for micro-planning, catch-up strategies, and the design of outbreak responses [ 5 – 7 , 10 – 12 ]. Type-specific immunity remains central in the bivalent oral poliovirus vaccine (bOPV) plus inactivated poliovirus vaccine (IPV) era, particularly for poliovirus type-2 following the global switch from tOPV to bOPV in 2016. Studies from Vietnam illustrate the role of IPV in closing the type-2 immunity gaps after the switch, aligning with the needs of programs confronting cVDPV2 risk [ 13 ]. Urban and special-population studies have further demonstrated how local immunization histories, migration, and occupational exposures shape antibody profiles; for example, healthcare professionals in Brazil and newly resettled refugees in Denmark exhibited distinct seroprotection patterns that informed targeted interventions [ 8 , 9 ]. In West and Central Africa, serosurveys conducted among adults and children have provided insights into residual susceptibility in complex delivery environments, thereby informing resource prioritization and guiding the refinement of supplementary immunization activities [ 5 , 11 , 12 ]. Methodological considerations are also crucial factors in interpreting seroprevalence. A comparative evaluation of virus-neutralization assays highlights variability across platforms. It underscores the value of harmonization for non-polio enteroviruses, a lesson that translates to poliovirus serology, that host and delivery-system factors, such as seasons of vaccination, prior exposures, and cohort effects, can influence measured antibody levels, reinforcing the need for locally generated estimates rather than reliance on global averages [ 14 – 17 ]. Although outside the scope of poliovirus, studies of other vaccine-preventable and viral infections (e.g., varicella disease burden, pertussis, mumps, hepatitis B) and even enterovirus surveillance in animal reservoirs collectively demonstrate how serology guides prevention policy when routine data are insufficient [ 17 – 20 ]. In Pakistan, districts categorized as very high-risk districts (VHRDs) concerning polio cases share characteristics commonly observed in other high-risk settings, including population mobility, missed opportunities for routine vaccination, hard-to-reach communities, and a recurrent need for targeted campaigns. In this context, a seroprevalence survey among children in VHRDs was essential to quantify seroprotection against poliovirus types 1, 2, and 3 after years of bOPV/IPV use and targeted responses, as well as risk factors associated with immunity levels. It was also imperative to generate district-level evidence to direct outreach and microplanning. By situating Pakistan’s estimates within the context of international experiences, including urban serosurveys, refugee populations, and post-switch evaluations, this study aims to provide decision-oriented immunity maps that support risk-based strategies for the eradication of poliovirus [ 6 , 7 , 13 , 16 , 21 ]. Materials and methods Study design and participants We conducted a district-specific cross-sectional seroprevalence survey across 44 very high-risk districts of Pakistan, identified by the National Emergency Operation Center (NEOC) due to persistent poliovirus detection in 2022 (Supplementary Table 1a). These districts served as geographical strata for this survey. Children were stratified into two age cohorts (6–11 months and 12–23 months) and included in the survey. Sample Size The sample size for this survey was calculated based on an assumed true seroprevalence of 90% and a 95% confidence interval with a ± 5% margin of error. A design effect of 1.5 and an anticipated response rate of 90% were considered. This resulted in a required sample size of 210 children per age cohort per stratum (district), totaling 420 children from each district across both age cohorts. Sampling Procedure To draw the sample from the target districts, a 1 x 1 km grid was generated over each district using ArcGIS (version 10.2.2). Grids with no residential population were excluded. Only grids with a population greater than 100 and neighboring grids with more than 300 individuals were combined to form the sampling frame. For proportional representation, stratified random sampling was employed at the tehsil (sub-districts) level. In each tehsil, probability proportional to size (PPS) was applied so that grids with larger populations had a higher chance of being selected. A total of 25 clusters were randomly selected per district, with an additional five clusters per district identified as backups. Overall, 1100 clusters were included in the survey design from the 44 target districts, with 125 backup clusters. Data Collection Web-based district maps were generated using Google's application programming interfaces (APIs) and uploaded onto handheld devices to guide data collectors. Each map displayed cluster boundaries, cluster extension boundaries, and centroids to ensure accurate navigation to households. Data collection was completed in two phases across the provinces between September 2022 and October 2023. A structured questionnaire was designed to be administered to mothers or caregivers of the target children, collecting information on household demographics and socioeconomic status, as well as child history, including vaccination status, for all children enrolled in the survey. Data on vaccination were recorded from vaccination cards, and in the absence of cards, data were collected through mother/caregiver recall. Along with the data, 2 mL of venous blood was obtained from each child by a trained phlebotomist. During the surveys, households that were locked or those that refused to participate were not replaced with other households. The data collection team in the district consisted of two female data collectors, two female phlebotomists, and a male team leader. The team received a comprehensive training, conducted over five days, led by experienced investigators and faculty members from Aga Khan University. Laboratory methodology After blood collection from a child, each sample was centrifuged, and the serum was isolated and put into sterile, labeled cryovials. The cryovials were stored in a cold box with ice packs and sent immediately to the nearest laboratory collection point of AKU. From these collection points, the samples were transported to the Nutrition Research Laboratory at AKU in Karachi. During the transportation, the temperature of the samples was monitored using a digital thermometer attached to the lid of the ice box. At the laboratory at AKU, two distinct aliquots were prepared; one was kept as a backup, and the other was sent to the National Institute of Health (NIH), Pakistan, for neutralization assay examination [ 22 ]. For this study, seropositivity was defined as a titer of poliovirus neutralizing antibody greater than 1:8 [ 23 ]. Statistical analysis Seroprevalence was estimated for poliovirus types 1, 2, and 3 by age cohort, child sex, and province. Point estimates were reported at 95% confidence intervals to account for the survey design effect. Immunity gaps were explored by stratifying results by demographic and geographic characteristics. Bivariate analyses were performed to examine the associations between seronegativity and selected covariates, including child age, sex, province of residence, maternal literacy, socioeconomic indicators, and vaccination history, such as receipt of IPV and full immunization status. For categorical variables, the Chi-square test was used with a significance level set at p < 0.05. Multivariate logistic regression models were fitted to identify independent predictors of seronegativity for each poliovirus type. Adjusted odds ratios (AORs) at 95% CIs were reported. Model specification considered potential confounders identified a priori from the literature, as well as variables significant at p < 0.2 in univariate analysis. Sensitivity analyses were performed to assess the robustness of estimates by excluding children with incomplete vaccination histories and stratifying the results by urban–rural residence. The analysis was conducted using STATA version 18 [ 24 ]. Ethical approval We obtained ethical approval from the Ethical Review Committee of Aga Khan University, Pakistan (2022-7646 ) , and the National Bioethics Committee, Pakistan (NBC-814). Informed consent was obtained from the caregivers of the participants included in the study. Results A total of 20,680 children were included (10,112 aged 6-11 months and 10,568 aged 12-23 months); the mean age was 13.5±5.3 months (8.9±1.7 and 17.9±3.5 months for the two cohorts, respectively). Gender distribution was balanced (52.0% male overall; 51.5% and 52.4% in the younger and older cohorts, respectively). Most participants were from Khyber Pakhtunkhwa (KP) (37.0%), followed by Sindh (27.2%), Balochistan (22.4%), Punjab (11.2%), and ICT (2.3%). The provincial distribution was similar across age groups. Over half lived in households with ≥7 members (53.4% ). Socioeconomic status was evenly distributed across wealth quintiles (~20% in each). Overall, maternal literacy was recorded at 63.7% (Table 1). Of the children included in the survey, 55.2% had received IPV, with a higher proportion of children in the 12-23-month age group than in the 6–11-month age group (61.3% vs 48.8%, respectively). Altogether, only 31.3% of children received four or more doses of OPV (33.6% of those 12-23 months old and 28.9% in the 6-11 months age group). Overall, 37.2% of children were fully immunized[1], and 44.8% were partially immunized. The proportion of fully immunized children was higher among those in the 6-11 months cohort (42.6%) compared to the 12-23 months cohort (32.0%). A higher proportion of children in the older age cohort were partially immunized (51.1%) compared to those in the younger age cohort (38.2%). District-wise demographic indicators are present in Supplementary Table 1a. Table 1 . Demographic indicators, residence, and vaccination history of the study population Total 6-11 months 12-23 months N=20680 N=10112 N=10568 Mean age (months) 13.5 ± 5.3 8.9 ± 1.7 17.9 ± 3.5 Gender of Child Male 10,751 (52.0%) 5,210 (51.5%) 5,541 (52.4%) Female 9,929 (48.0%) 4,902 (48.5%) 5,027 (47.6%) Province Punjab 2,307 (11.2%) 1,106 (10.9%) 1,201 (11.4%) Sindh 5,617 (27.2%) 2,739 (27.1%) 2,878 (27.2%) Balochistan 4,632 (22.4%) 2,342 (23.2%) 2,290 (21.7%) KPK 7,654 (37.0%) 3,696 (36.6%) 3,958 (37.5%) ICT 470 ( 2.3%) 229 ( 2.3%) 241 ( 2.3%) Family size =7 11,048 (53.4%) 5,310 (48.1%) 5,738 (51.9%) Wealth Quintiles Poorest 4,116 (19.9%) 2,058 (50.0%) 2,058 (50.0%) Poor 4,143 (20.0%) 2,058 (49.7%) 2,085 (50.3%) Middle 4,167 (20.1%) 2,028 (48.7%) 2,139 (51.3%) Rich 4,132 (20.0%) 1,975 (47.8%) 2,157 (52.2%) Richest 4,122 (19.9%) 1,993 (48.4%) 2,129 (51.6%) Mother education Literate 7,513 (36.3%) 3,644 (36.0%) 3,869 (36.6%) Illiterate 13,167 (63.7%) 6,468 (64.0%) 6,699 (63.4%) Child ever received IPV Yes 11,409 (55.2%) 4,936 (48.8%) 6,473 (61.3%) No 9,271 (44.8%) 5,176 (51.2%) 4,095 (38.7%) Total OPV doses (RI + SIAs) =4 6,479 (31.3%) 2,926 (28.9%) 3,553 (33.6%) Immunization status Not immunized 3,733 (18.1%) 1,946 (19.2%) 1,787 (16.9%) Partially immunized 9,260 (44.8%) 3,860 (38.2%) 5,400 (51.1%) Fully immunized 7,687 (37.2%) 4,306 (42.6%) 3,381 (32.0%) Abbreviations: KP: Khyber Pakhtunkhwa; ICT: Islamabad Capital Territory; IPV: Inactivated Poliovirus Vaccine; OPV: Oral Poliovirus Vaccine; RI: Routine Immunization; SIAs: Supplementary Immunization Activities. Seroprevalence of poliovirus types 1, 2, and 3 by age cohort and province Overall, seroprevalence for type 1 was 94.5% (CI: 94 – 95) and 95.9% (CI: 95.5 – 96.3) among children 6-11 months and 12-23 months, respectively. The seroprevalence was uniformly high (>94%) across all provinces with minimal age-related differences. On the contrary, type 2 displayed a substantial immunity gap, particularly in younger children, 44.6%(CI: 43.6 – 45.6), compared to the older age cohort, 53.8% (CI: 52.8 – 54.8), with the lowest levels in Baluchistan 39% (CI: 37 – 41) among the younger age cohort, 41.7% (CI: 39.7 – 43.7) among the older age cohort] and Sindh [37.5% (CI: 35.7 – 39.3) younger age cohort, and 50% (CI: 48.2 – 51.8) among older age cohort)]. Districts in Baluchistan and Sindh had low type 2 immunity compared to districts in other provinces (Supplementary Table 1b). The prevalence of type 3 seroprotection showed intermediate protection, above 90% for all provinces and both age cohorts except in Balochistan [79.5% (95% CI: 77.8 – 81.2) for younger age cohort] and [82.6% (CI:81.1 – 84.2) for older age cohort] and in KP for younger age cohort [89.2% (CI: 88.2 – 90.2 compared to 92.8% (CI: 92.0 – 93.6)]. Half of the districts in Baluchistan had low type immunity among younger children (Supplementary Table 1b). Overall, protection was stronger for type 1, weaker for type 2, and moderate for type 3, with Baluchistan consistently lagging and ICT maintaining the highest immunity across all serotypes. (Figure. 1). Reverse cumulative distributions of neutralizing antibody titters for poliovirus types 1, 2, 3 by age cohort and province. The strength of immunity was assessed through the reverse cumulative distribution of neutralizing antibody titers for poliovirus types 1, 2, and 3 in children aged 6-11 months (a, c, e) and 12-23 months (b, d, f) across the provinces (Figure 2). The higher the right-shifted curves, the stronger the immunity. Poliovirus type 1 (PV1) exhibits near-universal, high-titer protection across provinces, with ICT and Punjab showing the highest titters and Baluchistan the lowest; older children have slightly higher titters. Poliovirus type 2 (PV2) exhibits the weakest immunity, with a steep drop in titters after reaching low levels, highlighting significant gaps in Baluchistan and Sindh. In contrast, ICT and KP show comparatively better results, with older children again displaying modestly higher titters. Poliovirus type 3 (PPV3) lies between PV1 and PV2, offering generally strong protection but lower than PV1, and Baluchistan consistently lags behind. Overall, the figure demonstrates robust PV1 and PV3 immunity, but persistent gaps in PV2 immunity, especially among younger children and in Sindh and Balochistan. Risk factors associated with poliovirus seronegativity: Univariate and multivariate analysis We assessed risk factors associated with poliovirus seroprevalence using the univariate and multivariate models. Sero-negativity was highest in Baluchistan (8.0%) and KP (3.0%) compared to Punjab (1.1%), Sindh (1.7%), and ICT (0.9%). In the adjusted model, children from Baluchistan have significantly lower odds of seropositivity (AOR 0.178, CI: 0.066 - 0.484; p<0.001). A nonlinear association was found between household wealth and level of seroprotection, with nonsignificant differences between the poorest and richest groups (AOR 1.105, 95% CI: 0.816 – 1.496, p = 0.520). Children in the older age cohort were more likely to be seroprotected compared to the younger age cohort (AOR 1.356, 95% CI: 1.161 – 1.583, p<0.001). Also, receiving <4 doses of OPV had 1.2 times higher odds of seroprotection (AOR 1.25, 95% CI: 1.021 – 1.529, p= 4 doses (Table 2). A clear association was observed between immunization and immunity level: non-immunized children had the highest sero-negativity (7.8%), partially immunized children showed relatively higher protection (AOR 3.846, CI: 2.99 – 4.947; p < 0.001), while being fully immunized was significantly associated with higher seroprotection. A fully immunized child is 2 times more protected compared to a non-immunized child (AOR 2.004, 95% CI: 1.643 – 2.444, p<0.001). Table 2. Univariate and Multivariate Analysis for Risk Factors Associated with Seroprevalence Unadjusted Odds Ratio for Seropositivity P-values Adjusted Odds Ratio for Seropositivity P-values Any Type Poliovirus Seronegative Seropositive N=708 N=19,409 Province Punjab 24 ( 1.1%) 2,231 (98.9%) 0.861 (0.297,2.493) 0.782 0.695 (0.238,2.026) 0.505 Sindh 94 ( 1.7%) 5,414 (98.3%) 0.533 (0.195,1.458) 0.220 0.668 (0.243,1.835) 0.433 Balochistan 362 ( 8.0%) 4,138 (92.0%) 0.106 (0.039,0.285) <0.001 0.178 (0.066,0.484) 0.001 KPK 224 ( 3.0%) 7,194 (97.0%) 0.297 (0.110,0.803) 0.017 0.415 (0.153,1.127) 0.084 ICT 4 ( 0.9%) 432 (99.1%) Ref. Ref. Family size =7 455 ( 4.2%) 10,289 (95.8%) 0.627 (0.537,0.733) <0.001 Wealth Quintiles Poorest 146 ( 3.6%) 3,884 (96.4%) Ref. Ref. Poor 169 ( 4.2%) 3,888 (95.8%) 0.865 (0.690,1.084) 0.207 0.885 (0.702,1.116) 0.302 Middle 186 ( 4.6%) 3,850 (95.4%) 0.778 (0.624,0.971) 0.026 0.679 (0.54,0.854) 0.001 Rich 136 ( 3.4%) 3,876 (96.6%) 1.071 (0.845,1.359) 0.570 0.74 (0.579,0.946) 0.016 Richest 71 ( 1.8%) 3,911 (98.2%) 2.071 (1.554,2.759) <0.001 1.105 (0.816,1.496) 0.520 Mother education Literate 158 ( 2.2%) 7,148 (97.8%) 2.029 (1.696,2.428) <0.001 Illiterate 550 ( 4.3%) 12,261 (95.7%) Ref. Sex of Child Male 357 ( 3.4%) 10,079 (96.6%) 1.062 (0.914,1.234) 0.431 Female 351 ( 3.6%) 9,330 (96.4%) Ref. Child age 6-11 months 409 ( 4.2%) 9,377 (95.8%) Ref. Ref. 12-23 months 299 ( 2.9%) 10,032 (97.1%) 1.463 (1.257,1.703) <0.001 1.356 (1.161,1.583) <0.001 Child ever received IPV Yes 230 ( 2.1%) 10,892 (97.9%) Ref. No 478 ( 5.3%) 8,517 (94.7%) 0.376 (0.321,0.441) <0.001 Total OPV doses (RI + SIAs) <4 505 ( 3.7%) 13,328 (96.3%) 0.881 (0.747,1.040) =4 203 ( 3.2%) 6,081 (96.8%) Ref. Ref. Immunization status Not immunized 280 ( 7.8%) 3,312 (92.2%) Ref. Ref. Partially immunized 146 ( 1.6%) 8,884 (98.4%) 5.144 (4.195,6.309) <0.001 3.846 (2.99,4.947) <0.001 Fully immunized 282 ( 3.8%) 7,213 (96.2%) 2.162 (1.824,2.564) <0.001 2.004 (1.643,2.444) <0.001 [1] A child was categorized as fully immunized when s/he completed vaccination from birth through the first dose of measles-containing vaccine (MCV1), which is scheduled to be given at nine months of age as per the Expanded Program on Immunization (EPI), Pakistan, i.e., BCG, OPV0, OPV1-3, Penta1-3, PCV1-3, IPV, and MCV1. This definition excludes Hep-B at birth, ROTA 1at six weeks, ROTA 2 at ten weeks, and TCV at nine months. Discussion This seroprevalence survey, conducted in 44 very high-risk districts of Pakistan, provides one of the most granular assessments of poliovirus immunity among children in recent years. Our results showed that overall population-level immunity remains high for the type I strain, with more than 94% of children showing serological evidence of protection. However, significant variability in immunity levels persists across age groups and regions, and immunity gaps exist for virus types 2 and 3, similar to patterns observed in other endemic regions. The findings highlight both the progress made and the fragility of eradication efforts, especially regarding poliovirus types 2 and 3 among the target age groups. Our results for type 1 are consistent with findings from other studies in diverse settings. An Afghan serological survey conducted in 2017 also recorded similarly high type 1 immunity in children under two years of age [25]. Additionally, in India, seroprotection for type 1 polio was over 95% in Uttar Pradesh – a polio high-risk region - before the disruption of wild poliovirus transmission [26]. Likewise, in West Africa, serosurveys in Nigeria and Chad also observed greater protection against type 1 in zones where intensive SIAs were conducted [27, 28]. These convergent findings suggest that, despite operational weaknesses, frequent OPV exposure has been sufficient to maintain high immunity against type 1 in various settings. Conversely, our findings of low immunity level for the type 2 strain reflect the global consequence of the tOPV withdrawal in 2016. In the post-switch period, type 2 seroprevalence in Pakistan declined below 50% among children under two years, especially in children with low IPV coverage [3]. A multi-country analysis of poliovirus immunity levels reported that type 2 immunity declined steeply two to three years after the global post-switch, particularly in regions with suboptimal IPV coverage [29]. A similar trend was reported in Nigeria, where type 2 population immunity decreased after the transition, leading to recurrent outbreaks of circulating vaccine-derived poliovirus type 2 (cVDPV2) [30]. A study from Syria showed that large cVDPV2 outbreaks after tOPV withdrawal unveiled immunity gaps among children under two years of age, via low IPV uptake and immunization disruption due to conflict [31]. Our reverse cumulative titer curves for type 2 immunity showed that protection in the target regions is weak in strength and low in coverage, with much lower median titers. The results are consistent with known immunological limitations of IPV, which induces predominantly systemic humoral responses but fails to induce lasting mucosal immunity. Findings from a randomized controlled trial in India indicated that a single dose of IPV is sufficient to enhance type 2 immunity. Still, restoration of population immunity is only with increasing coverage and, in specific settings, targeted use of monovalent OPV (mOPV) [32]. The low median titers in our study, particularly in more classically high-risk settings, suggest that, apart from IPV's general failure to elicit intestinal immunity, systemic immunity per se is similarly suboptimal in such groups, presumably due to an incompletely vaccinated population, missed doses, or loss of antibody. Combined, these double vulnerabilities underscore the heightened risk of children in such settings being exposed to poliovirus circulation. Seroprotection against poliovirus type 3 in our study was lower compared to the level of immunity level, and showed extensive provincial variation, with the lowest rates in Baluchistan. This finding is consistent with global evidence that type 3 immunity lags type 1, even in countries with higher routine immunization coverage. The Type 3 component of OPV is less immunogenic than the Type 1 component, and seroconversion requires multiple doses. In India and Pakistan, type 3 seroprevalence generally lagged behind type 1 by 5–10 percentage points, both due to its diminished immunogenicity and irregular SIA quality [26]. These disparities have also been observed in Nigeria and South Africa, where type 3 immunity consistently fell below the level required to break transmission [27, 33]. Comparisons highlight that type 3 is an ongoing issue across the world, where not only routine vaccination but also high-quality SIAs are required in low coverage pockets of the population. The gradient of age in our findings, with older children aged 12–23 months having higher immunity to all serotypes, reflects cumulative exposure from routine immunization and campaigns. Such age effects have been observed earlier in India, Nigeria, and Afghanistan, where younger children typically exhibit lower seroprevalence until more doses of OPV are administered [27, 34, 35]. Similarly, cross-sectional studies in China and Cameroon have also reported the same trends [10, 12]. Also, Pakistan-specific studies have consistently demonstrated similar trends [36,37]. The continuity of these trends at the regional levels is a sign of missed opportunities during the first year of life, reflecting gaps in routine immunization, integration of services with maternal and child health, and the effectiveness of SIAs. They emphasize the need for effective and timely routine immunization to fill immunity gaps among the most vulnerable age groups. Our analysis identifies key demographic and programmatic factors influencing poliovirus seroprevalence in Pakistan. Geographic inequity was evident in Balochistan, whereby children had significantly lower odds of seropositivity compared with other provinces, even after adjusting for confounding factors. This finding aligns with sustained concerns about programmatic challenges in Balochistan, including security-related restrictions, weak health infrastructure, and widespread population mobility. These geographic variations in immunity have also been reported in northern Nigeria and Afghanistan, where ongoing reservoirs of incompletely immunized children have caused poliovirus transmission despite very high immunization coverage at the national level [34, 35]. Maternal literacy was highly correlated with seroprotection in our unadjusted model, and mothers whose children were literate were likely to be tested seropositive. This finding aligns with earlier studies conducted in Pakistan and other low- and middle-income countries, which have demonstrated that caregiver education improves health-seeking behavior and vaccine coverage [34, 35, 38]. While attenuated in the adjusted model, the direction of the association serves to emphasize the continued influence of social determinants on immunity outcomes. Household wealth had a nonlinear effect on seroprotection level in our study. Children in the wealthiest quintile had no appreciably greater odds of seropositivity compared to those in the poorest quintile. However, those in the more affluent and intermediate quintiles had decreased odds. The contradictory trends are hypothesized to indicate that the economic slopes of immunity to polio might be more complex than those for other childhood vaccines, perhaps because of the widespread use of mass campaigns that span socioeconomic lines. However, data from international eradication contexts indicate that socioeconomic disadvantage remains a persistent risk factor for underimmunization, particularly in areas where routine service availability is limited [27, 34, 35]. Vaccination history was one of the major predictors of seroprotection. Children who were not immunized were most seronegative, whereas partially and fully immunized children had significantly higher odds of being seropositive, indicating the direct effect of full immunization on immunity. Similar findings were reported in a study from Nigeria, where missing doses or incomplete doses were the most persistent predictors of susceptibility [27]. Contrary to previous studies, our analysis revealed that children who reported receiving fewer than four doses of OPV had marginally higher adjusted odds of seropositivity compared to those who received four or more doses [36, 39]. This seeming paradox may have occurred due to parental recall bias, misclassification of vaccine doses during recall, or differential campaign performance, where fewer but more intense exposures were administered. This inconsistency needs closer attention, most importantly by validation of vaccination history against independent records. Together, these results show that a dynamic interplay of geographic, demographic, and programmatic factors shapes Pakistan's poliovirus immunity. Structural disparities, the impact of maternal education, and the priority of universal immunization all make it clear that eradication is both a social and biomedical challenge. Continued progress will entail not just high rates of coverage through routine and supplemental campaigns but also interventions aimed at eliminating regional and social disparities that continue to propel transmission. This study is not without limitations. Its cross-sectional nature constrains causal inferences from individual-level changes in immunity. The history of vaccination was partially ascertained by caregiver report in the absence of vaccination cards. This is likely to result in the unintentional recall bias for vaccination status. Neutralizing antibody titers are a measurement of humoral immunity. Still, they will not necessarily capture mucosal immunity that is essential for breaking the transmission of poliovirus, especially when using the oral polio vaccine. Contextual factors, such as seasonal migration, access issues, and overlapping supplementary immunization activities during the survey period, could have affected both vaccination exposure and seroprevalence measured, possibly limiting generalizability. Despite this, our findings reveal prevalence and inequalities in poliovirus immunity in high-risk regions of Pakistan, providing evidence for targeted programmatic interventions. Conclusion Our findings underscore the necessity of addressing immunity gaps in types 2 and 3 in Pakistan's polio program, especially for younger children in the high-risk areas. Enhancing the' quality and reach of OPV campaigns, expanding IPV coverage, and integrating immunization with maternal and child health services are crucial for ensuring protection in the early years of life. Simultaneously addressing vaccine hesitancy and building trust through sustained community involvement would help to strengthen the approach towards poliovirus eradication in the country. Declarations Author Contributions: SBS conceptualized and designed the survey and assisted with interpreting the results. IH developed the sampling strategy and tools and supervised the field activities. AK, AH and MU jointly drafted the manuscript. MU assisted with study design, formulating contextually relevant survey tools, and oversaw data collection activity. MS performed the statistical analysis. MMA supervised the laboratory analysis of the samples. MAH, AB, RH, JF, and all authors reviewed and approved the final manuscript for submission. Declaration of competing interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Data availability: The data will be made available upon request. Acknowledgment: We are immensely grateful to all participants for their cooperation during the survey. Funding sources: The study was supported by the Bill & Melinda Gates Foundation [grant number OPP1156736]. References World Health Organization. Two out of three wild poliovirus strains have been eradicated. Accessed September 07, 2025. https://www.who.int/news-room/feature-stories/detail/two-out-of-three-wild-poliovirus-strains-eradicated Global Polio Eradication Initiative (GPEI). Global eradication of wild poliovirus type 2 declared - GPEI. Accessed September 07, 2025. https://polioeradication.org/news/global-eradication-of-wild-poliovirus-type-2-declared/ Hussain I, Umer M, Khan A, Sajid M, Ahmed I, Begum K, Iqbal J, Alam MM, Safdar RM, Baig S, Voorman A, Partridge J, and Soofi S (2024). Exploring the path to polio eradication: insights from consecutive seroprevalence surveys among Pakistani children. Front. Public Health 12:1384410. doi: 10.3389/fpubh.2024.1384410 Polio cases in Pakistan | District-wise. Accessed September 07, 2025. https://www.endpolio.com.pk/polioin-pakistan/district-wise-polio-cases Alfonso VH, Voorman A, Hoff NA, et al. Poliovirus immunity among adults in the Democratic Republic of the Congo: a cross-sectional serosurvey. BMC Infect Dis. 2022;22(1):30. doi: 10.1186/s12879-021-06951-6 Kohmer N, Rabenau HF, Rilling V, Ciesek S, Enders M, Eggers M. Polio type 2 and 3 eradication: Relevance to the immunity status of individuals living in Germany, 2005–2020. J Clin Virol. 2023;164:105471. doi: 10.1016/j.jcv.2023.105471 Wallace, G.S., Curns, A.T., Weldon, W.C. et al. Seroprevalence of Poliovirus Antibodies in the United States Population, 2009–2010. BMC Public Health 16, 721 (2016). https://doi.org/10.1186/s12889-016-3386-1 Hvass AMF, Wejse C. High coverage of polio immunization program in refugees resettling in Denmark. A cross-sectional study of polio serology in newly arrived refugees. Expert Rev Vaccines. 2019;18(12):1317–1322. doi: 10.1080/14760584.2019.1698953. Epub 2019 Dec 10. PMID: 31771367.H Moraes JC, Rujula MJP, Otsuka M. Prevalence of Neutralizing Antibodies Against Poliovirus 1, 2, and 3 in healthcare professionals aged 20–50 years. Rev Paul Pediatr. 2021;39:e2019354. doi: 10.1590/1984-0462/2021/39/2019354 . Xu J, Kuang S, Rong R, Zhang Y, Tang W, Wang Q. Sero-survey of polio antibodies and quality of acute flaccid paralysis surveillance in Chongqing, China: A cross-sectional study. Medicine (Baltimore). 2020;99(31):e21298. doi: 10.1097/MD.0000000000021298 . Bolu O, Adamu U, Franka R, Umeokonkwo CD, An Q, Greby S, McDonald S, Mainou B, Mba N, Agala N, Archer WR, Braka F, Etapelong SG, Gashu TS, Siddique AR, Asekun A, Okoye M, Iriemenam N, Wiesen E, Swaminathan M, Ihekweazu C, Shuaib F. Seroprevalence of poliovirus antibodies in Nigeria: refining strategies to sustain the eradication effort. Pan Afr Med J. 2023;45(Suppl 2):2. doi: 10.11604/pamj.supp.2023.45.2.38098. . Claire Endegue M, Sein C, Lopez Cavestany R, Jeyaseelan V, Palmer T, Norbert Soke G, Diaha A, Jafri B, Mainou BA, Verma H, Mach O. Community-based survey to assess seroprevalence of poliovirus antibodies in far-north Cameroon in 2020. Vaccine X. 2022;12:100244. doi: 10.1016/j.jvacx.2022.100244.C Huyen DTT, Mach O, Thanh Trung N, Thai PQ, Thang HV, Weldon WC, Oberste MS, Jeyaseelan V, Sutter RW, Anh DD. Rapid Disappearance of Poliovirus Type 2 (PV2) Immunity in Young Children Following Withdrawal of Oral PV2-Containing Vaccine in Vietnam. J Infect Dis. 2019;220(3):386–391. doi: 10.1093/infdis/jiz124 . Abreu TC, Boshuizen H, Mollema L, Berbers GAM, Korthals Altes H. Association between season of vaccination and antibody levels against infectious diseases. Epidemiol Infect. 2020;148:e276. doi: 10.1017/S0950268820002691 . Karelehto E, Koen G, Benschop K, van der Klis F, Pajkrt D, Wolthers K. Enterovirus D68 serosurvey: evidence for endemic circulation in the Netherlands, 2006 to 2016. Euro Surveill. 2019;24(35):1800671. doi: 10.2807/1560-7917.ES.2019.24.35.1800671 . Wang J, Wu W, Wang W, Zhang J, Xiao J, Cai M, Guo J, Li R, Zhu S, Zhang W, Chen M, Teng Z. Seroprevalence of neutralizing antibodies against HFMD associated enteroviruses among healthy individuals in Shanghai, China, 2022. Virol Sin. 2024;39(4):694–698. doi: 10.1016/j.virs.2024.05.008 . Doshi RH, Alfonso VH, Hoff NA, Mukadi P, Gerber S, Bwaka A, Higgins SG, Mwamba GN, Okitolonda E, Muyembe JJ, Rimoin AW. Evidence of Mumps Infection Among Children in the Democratic Republic of Congo. Pediatr Infect Dis J. 2017;36(5):462–466. doi: 10.1097/INF.0000000000001483 . Sytiuk MP, Bezymennyy MV, Halka IV, Uhovskyy VV, Muzykina LM, Lavalley M, Nychyk SA, Nedosekov VV, Howard MW, Bortz E. Seroprevalence of Enzootic Teschen Disease in the Wild Boar Population in Ukraine. Vector Borne Zoonotic Dis. 2022;22(2):138–147. doi: 10.1089/vbz.2021.0063.Syt . Umego CF, Mboto CI, Asitok AD, Osaji LC, George UE, Edet UO, Mbim EN, Faleye TO, Adewumi OM, Adeniji JA. Circulation of hepatitis B virus genotype-E among outpatients in tertiary hospitals in the Niger-Delta region of Nigeria. Afr Health Sci. 2022;22(1):511–520. doi: 10.4314/ahs.v22i1.60 . Van Lier A, de Gier B, McDonald SA, Mangen MJ, van Wijhe M, Sanders EAM, Kretzschmar ME, van Vliet H, de Melker HE. Disease burden of varicella versus other vaccine-preventable diseases before introduction of vaccination into the national immunisation programme in the Netherlands. Euro Surveill. 2019;24(18):1800363. doi: 10.2807/1560-7917.ES.2019.24.18.1800363 . Couderé K, Benschop KSM, Koen G, van Eijk H, Harvala H, Bailly JL,et al. Assessment of twelve echovirus virus-neutralisation assays in Europe: recommendations for harmonisation of non-polio enterovirus sero-surveillance studies. J Gen Virol. 2024;105(9). doi: 10.1099/jgv.0.001986 . Weldon WC, Oberste MS, MA P. Standardized methods for detection of poliovirus antibodies. New York: Springer (2016). Plotkin SA. Correlates of protection induced by vaccination. Clin Vaccine Immunol. (2010) 17:1055–65. doi: 10.1128/CVI.00131-10 StataCorp. Stata Statistical Software: Release 17. College Station, TX: StataCorp LLC.; 2025. Hussain I, Mach O, Hamid NA, Bhatti ZS, Moore DD, Oberste MS, Khan S, Khan H, Weldon WC, Sutter RW, Bhutta ZA, Soofi SB. Seroprevalence of anti-polio antibodies in children from polio high risk area of Afghanistan: A cross sectional survey 2017. Vaccine. 2018;36(15):1921–1924. doi: 10.1016/j.vaccine.2018.02.055 . Sunil Bahl, Howard E. Gary, Hamid Jafari, Bidyut K. Sarkar, Surendra K. Pathyarch, Raman Sethi, Jagadish Deshpande, An Acute Flaccid Paralysis Surveillance–Based Serosurvey of Poliovirus Antibodies in Western Uttar Pradesh, India, The Journal of Infectious Diseases, Volume 210, Issue suppl_1, November 2014, Pages S234–S242, https://doi.org/10.1093/infdis/jiu379 Etsano A, Damisa E, Shuaib F, Nganda GW, Enemaku O, Usman S, Adeniji A, Jorba J, Iber J, Ohuabunwo C, Nnadi C, Wiesen E. Environmental Isolation of Circulating Vaccine-Derived Poliovirus After Interruption of Wild Poliovirus Transmission - Nigeria, 2016. MMWR Morb Mortal Wkly Rep. 2016;65(30):770–3. doi: 10.15585/mmwr.mm6530a4 . Gamougam K, Jeyaseelan V, Jones KAV, Mainou BA, Palmer T, Diaha A, Wiesen E, Ntezayabo B, Ayangma R, Soke NG, Samba D, Okiror S, Mach O. A Survey to Assess Serological Prevalence of Poliovirus Antibodies in Areas With High-Risk for Vaccine-Derived Poliovirus Transmission in Chad. J Pediatric Infect Dis Soc. 2022;11(2):55–59. doi: 10.1093/jpids/piab103 . PMID: 34791366; PMCID: PMC8865003. Voorman A, Lyons H, Bennette C, Kovacs S, Makam JK, F Vertefeuille J, Tallis G. Analysis of population immunity to poliovirus following cessation of trivalent oral polio vaccine. Vaccine. 2023;41 Suppl 1(Suppl 1):A85-A92. doi: 10.1016/j.vaccine.2022.03.013 . Burns CC, Shaw J, Jorba J, Bukbuk D, Adu F, Gumede N, Pate MA, Abanida EA, Gasasira A, Iber J, Chen Q, Vincent A, Chenoweth P, Henderson E, Wannemuehler K, Naeem A, Umami RN, Nishimura Y, Shimizu H, Baba M, Adeniji A, Williams AJ, Kilpatrick DR, Oberste MS, Wassilak SG, Tomori O, Pallansch MA, Kew O. Multiple independent emergences of type 2 vaccine-derived polioviruses during a large outbreak in northern Nigeria. J Virol. 2013;87(9):4907–22. doi: 10.1128/JVI.02954-12 . Mbaeyi C, Moran T, Wadood Z, Ather F, Sykes E, Nikulin J, Al Safadi M, Stehling-Ariza T, Zomahoun L, Ismaili A, Abourshaid N, Asghar H, Korukluoglu G, Duizer E, Ehrhardt D, Burns CC, Sharaf M. Stopping a polio outbreak in the midst of war: Lessons from Syria. Vaccine. 2021;39(28):3717–3723. doi: 10.1016/j.vaccine.2021.05.045 . Ahmad M, Verma H, Deshpande J, Kunwar A, Bavdekar A, Mahantashetti NS, Krishnamurthy B, Jain M, Mathew MA, Pawar SD, Sharma DK, Sethi R, Visalakshi J, Mohanty L, Bahl S, Haldar P, Sutter RW. Immunogenicity of Fractional Dose Inactivated Poliovirus Vaccine in India. J Pediatric Infect Dis Soc. 2022;11(2):60–68.). doi: 10.1093/jpids/piab091 Brown L, Bingham J, Pulliam J, Mthombothi Z, Sereo T, Kamupira M, Botha S, Molema K, Maseti E, Schönfeldt M, Mabhena N, Prabdial-Sing N, von Gottberg A, McCarthy K, van Schalkwyk C. Estimation of the poliovirus type 2 immunity gap in South Africa. Vaccine. 2024;42(23):126062. doi: 10.1016/j.vaccine.2024.06.029 . Odusanya, O.O., Alufohai, E.F., Meurice, F.P. et al. Determinants of vaccination coverage in rural Nigeria. BMC Public Health 8, 381 (2008). https://doi.org/10.1186/1471-2458-8-381 Aalemi AK, Shahpar K, Mubarak MY. Factors influencing vaccination coverage among children age 12–23 months in Afghanistan: Analysis of the 2015 Demographic and Health Survey. PLoS One. 2020;15(8):e0236955. doi: 10.1371/journal.pone.0236955 . Hussain I, Mach O, Habib A, Bhatti Z, Suhag Z, Oberste MS, Weldon WC, Sutter RW, Soofi SB, Bhutta ZA. Seroprevalence of Anti-polio Antibodies in Children From Polio High-risk Areas of Pakistan: A Cross-Sectional Survey 2015–2016. Pediatr Infect Dis J. 2017;36(9):e230-e236. doi: 10.1097/INF.0000000000001622 . Sodhar IA, Mehraj J, Hussaini AS, Aamir M, Mahsaud J, Ahmed S, Shaikh AA, Zardari AA, Rasool S, Chandio SA, Stuckey EM. Population Movement and Poliovirus Spread across Pakistan and Afghanistan in 2023. Vaccines (Basel). 2024;12(9):1006. doi: 10.3390/vaccines12091006 . Habib M, Soofi S, Ali N, Sutter RW, Palansch M, Qureshi H, Akhtar T, Molodecky NA, Okayasu H, Bhutta ZA. A study evaluating poliovirus antibodies and risk factors associated with polio seropositivity in low socioeconomic areas of Pakistan. Vaccine. 2013;31(15):1987–93. doi: 10.1016/j.vaccine.2013.02.003 . Iliyasu Z, Verma H, Craig KT, Nwaze E, Ahmad-Shehu A, Jibir BW, Gwarzo GD, Gajida AU, Weldon WC, Steven Oberste M, Takane M, Mkanda P, Muhammad AJG, Sutter RW. Poliovirus seroprevalence before and after interruption of poliovirus transmission in Kano State, Nigeria. Vaccine. 2016;34(42):5125–5131. doi: 10.1016/j.vaccine.2016.08.058 . Additional Declarations No competing interests reported. Supplementary Files Supplementaryfiles.docx Cite Share Download PDF Status: Published Journal Publication published 30 Dec, 2025 Read the published version in npj Vaccines → Version 1 posted Editorial decision: Revision requested 04 Nov, 2025 Reviews received at journal 23 Oct, 2025 Reviews received at journal 16 Oct, 2025 Reviews received at journal 15 Oct, 2025 Reviewers agreed at journal 14 Oct, 2025 Reviewers agreed at journal 13 Oct, 2025 Reviewers agreed at journal 13 Oct, 2025 Reviewers agreed at journal 08 Oct, 2025 Reviewers invited by journal 07 Oct, 2025 Editor assigned by journal 07 Oct, 2025 Submission checks completed at journal 30 Sep, 2025 First submitted to journal 20 Sep, 2025 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-7664228","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":531659976,"identity":"2d088683-b1e3-41fb-a94e-97c4314ee6e3","order_by":0,"name":"Imtiaz Hussain","email":"","orcid":"","institution":"The Aga Khan University","correspondingAuthor":false,"prefix":"","firstName":"Imtiaz","middleName":"","lastName":"Hussain","suffix":""},{"id":531659977,"identity":"d690b87e-a0b7-4ee2-9611-b1d41caec3ac","order_by":1,"name":"Ahmad Khan","email":"","orcid":"","institution":"The Aga Khan University","correspondingAuthor":false,"prefix":"","firstName":"Ahmad","middleName":"","lastName":"Khan","suffix":""},{"id":531659978,"identity":"aa7aa180-600b-46b7-83e5-03dac54444fe","order_by":2,"name":"Muhammad Umer","email":"","orcid":"","institution":"The Aga Khan University","correspondingAuthor":false,"prefix":"","firstName":"Muhammad","middleName":"","lastName":"Umer","suffix":""},{"id":531659979,"identity":"85667328-fea2-43f1-9593-49b8504d63a2","order_by":3,"name":"Muhammad Sajid","email":"","orcid":"","institution":"The Aga Khan University","correspondingAuthor":false,"prefix":"","firstName":"Muhammad","middleName":"","lastName":"Sajid","suffix":""},{"id":531659980,"identity":"7bc9b158-e5d4-46fb-b7c0-3388949aa734","order_by":4,"name":"Haider Abbass","email":"","orcid":"","institution":"The Aga Khan University","correspondingAuthor":false,"prefix":"","firstName":"Haider","middleName":"","lastName":"Abbass","suffix":""},{"id":531659981,"identity":"4c909bbb-a2b3-44ce-90af-c7f7a1bf72cf","order_by":5,"name":"Muhammad Masroor Alam","email":"","orcid":"","institution":"National Institute of Health","correspondingAuthor":false,"prefix":"","firstName":"Muhammad","middleName":"Masroor","lastName":"Alam","suffix":""},{"id":531659982,"identity":"272c21be-9442-434a-a3c8-95feeb88d770","order_by":6,"name":"Altaf Bosan","email":"","orcid":"","institution":"Polio National Emergency Operations Center, Govt of Pakistan","correspondingAuthor":false,"prefix":"","firstName":"Altaf","middleName":"","lastName":"Bosan","suffix":""},{"id":531659983,"identity":"43426854-831f-4df4-86eb-0801aa792de0","order_by":7,"name":"Jeffrey Partridge","email":"","orcid":"","institution":"Bill \u0026 Melinda Gates Foundation","correspondingAuthor":false,"prefix":"","firstName":"Jeffrey","middleName":"","lastName":"Partridge","suffix":""},{"id":531659984,"identity":"b5405ea5-4ddb-4c79-8690-afa47678a7f0","order_by":8,"name":"Anwarul Haq","email":"","orcid":"","institution":"Polio National Emergency Operations Center, Govt of Pakistan","correspondingAuthor":false,"prefix":"","firstName":"Anwarul","middleName":"","lastName":"Haq","suffix":""},{"id":531659985,"identity":"c14407d9-fb36-4742-b1ff-df71e21369c3","order_by":9,"name":"Rehan Hafiz","email":"","orcid":"","institution":"Bill \u0026 Melinda Gates Foundation","correspondingAuthor":false,"prefix":"","firstName":"Rehan","middleName":"","lastName":"Hafiz","suffix":""},{"id":531659988,"identity":"5f146cf2-3779-4510-9c75-33ae2503639d","order_by":10,"name":"Sajid Bashir Soofi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA20lEQVRIiWNgGAWjYHCChAM8IIr5YOMDhgNgAWK1sCU2GxCrhYEBoiWBTYIoLfLtBx4eeMNQJ8fPxtxW8ePMYQZ+9hwDvFoMziQkHJzDcNhYso2x7WbPjcMMkj1vCGhhSEg4zMNwIHHD/ca2GzwfDjMY3CBgi3z/A5CWusQNxxjbCv8AtdgT0sJwA2wLM1gLMw/QYQYShPxy4wHQLwZgvzRLy5xJ55E486yAgMNykj+8qQCFGPvDj2+OWcvxtydvwO8wBp4EUCAguASUgwD7ASIUjYJRMApGwYgGABEVTOsfCNy4AAAAAElFTkSuQmCC","orcid":"","institution":"The Aga Khan University","correspondingAuthor":true,"prefix":"","firstName":"Sajid","middleName":"Bashir","lastName":"Soofi","suffix":""}],"badges":[],"createdAt":"2025-09-20 10:08:28","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7664228/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7664228/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41541-025-01352-1","type":"published","date":"2025-12-30T15:57:23+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":93917123,"identity":"9fe4f6c9-b877-49a9-9feb-c7ae3c25429c","added_by":"auto","created_at":"2025-10-20 08:58:12","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":1490098,"visible":true,"origin":"","legend":"","description":"","filename":"Manuscript.docx","url":"https://assets-eu.researchsquare.com/files/rs-7664228/v1/8b7d14386106f1eb2ca363ea.docx"},{"id":93914887,"identity":"926d2516-8f4a-4972-99b1-b58aa10d54e5","added_by":"auto","created_at":"2025-10-20 08:42:12","extension":"json","order_by":1,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":10887,"visible":true,"origin":"","legend":"","description":"","filename":"1961ccd8827145aa9567b46941b60727.json","url":"https://assets-eu.researchsquare.com/files/rs-7664228/v1/766c5ff0f6747172116d0294.json"},{"id":93915942,"identity":"7158b84e-b46a-4171-8d86-06b7a3f67287","added_by":"auto","created_at":"2025-10-20 08:50:12","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":51938,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementaryfiles.docx","url":"https://assets-eu.researchsquare.com/files/rs-7664228/v1/8a604b6091a00620e471dc9e.docx"},{"id":93915944,"identity":"341dcd6f-9981-4dee-826c-e08f721fa55c","added_by":"auto","created_at":"2025-10-20 08:50:12","extension":"xml","order_by":3,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":153917,"visible":true,"origin":"","legend":"","description":"","filename":"1961ccd8827145aa9567b46941b607271enriched.xml","url":"https://assets-eu.researchsquare.com/files/rs-7664228/v1/69cc8de75015e510cef4d3e0.xml"},{"id":93914888,"identity":"6317cb4d-91f5-4ece-9ca1-1c1f07bc9768","added_by":"auto","created_at":"2025-10-20 08:42:12","extension":"jpeg","order_by":4,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":745474,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7664228/v1/a4136a8ec394c1b67e20323f.jpeg"},{"id":93914895,"identity":"e9b163fb-8729-42cc-9575-da9eaacd7879","added_by":"auto","created_at":"2025-10-20 08:42:12","extension":"emf","order_by":5,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":15899748,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage2.emf","url":"https://assets-eu.researchsquare.com/files/rs-7664228/v1/0d352b0d0921cff101b976d8.emf"},{"id":93914889,"identity":"8611fc90-4d8a-4dcb-9579-9ddc43de9705","added_by":"auto","created_at":"2025-10-20 08:42:12","extension":"png","order_by":6,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":90701,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7664228/v1/3cba51d424825ee1203aee9b.png"},{"id":93914892,"identity":"b96523c9-f6ed-4c19-97bd-26d3b1869705","added_by":"auto","created_at":"2025-10-20 08:42:12","extension":"png","order_by":7,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":458974,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7664228/v1/1d92d2bbdc517d1543f3497c.png"},{"id":93914891,"identity":"280478e6-c685-45f9-85eb-37315c028ad5","added_by":"auto","created_at":"2025-10-20 08:42:12","extension":"xml","order_by":8,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":151668,"visible":true,"origin":"","legend":"","description":"","filename":"1961ccd8827145aa9567b46941b607271structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7664228/v1/beaf7085128273884dd2e3c1.xml"},{"id":93914894,"identity":"566d8078-7d01-431e-bef0-845766cd8d16","added_by":"auto","created_at":"2025-10-20 08:42:12","extension":"html","order_by":9,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":161011,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7664228/v1/cf2d927e65cd8d09e7762250.html"},{"id":93914882,"identity":"4cfc91d5-fd39-457d-b6d9-87fd3cf9aa61","added_by":"auto","created_at":"2025-10-20 08:42:12","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":131499,"visible":true,"origin":"","legend":"\u003cp\u003eSeroprevalence of poliovirus types 1, 2, and 3 among children aged 6–11 months and 12–23 months across provinces and ICT\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7664228/v1/cf99737cdca4f37082d5ab21.png"},{"id":93914884,"identity":"1fbd8338-faf7-404a-a2a9-8c30f8ae25ad","added_by":"auto","created_at":"2025-10-20 08:42:12","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1244874,"visible":true,"origin":"","legend":"\u003cp\u003eReverse cumulative distributions of neutralizing antibody titers for poliovirus types 1–3 in children aged 6–11 and 12–23 months by province, showing strong PV1, intermediate PV3, and weakest PV2 immunity, with Baluchistan and Sindh consistently lowest.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7664228/v1/4f4b0aea3c24ec3fb050c656.png"},{"id":99545234,"identity":"38b11bb5-7586-4680-9765-49e379b73a11","added_by":"auto","created_at":"2026-01-05 16:03:30","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2201223,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7664228/v1/97ab2e8a-b87f-40b3-bda4-43c0c80d2103.pdf"},{"id":93914883,"identity":"1f15cb05-11b0-4e50-8258-94a5c914fa51","added_by":"auto","created_at":"2025-10-20 08:42:12","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":51938,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementaryfiles.docx","url":"https://assets-eu.researchsquare.com/files/rs-7664228/v1/0a28cd45676bb1ab0f018584.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Progress and gaps in poliovirus immunity: Evidence from a serological survey of children aged 6-23 months in high-risk districts of Pakistan","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePoliomyelitis remains a significant public health concern despite remarkable progress towards its global eradication. Caused by the poliovirus, an enterovirus mainly spread through the fecal-oral route, it can result in permanent paralysis and, in severe cases, death [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Following the launch of the Global Polio Eradication Initiative (GPEI) in 1988, there has been a decrease of more than 99% in the global incidence of polio. However, Pakistan and Afghanistan continue to be among the last two countries where the wild poliovirus (WPV) is still being transmitted [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. In Pakistan, WPV cases have been continuously reported over the years. In 2022, 20 WPV cases were reported in the country, followed by 6 cases in 2023, 74 cases in 2024, and 24 cases as of September 2025 [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eSustained progress towards polio eradication has fundamentally reshaped population immunity profiles, yet pockets of susceptibility persist where routine immunization and supplementary campaigns have been unevenly disturbed [\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Serological surveys provide programmatically actionable estimates of functional protection as they measure neutralizing antibodies directly, revealing gaps that administrative coverage of campaign tallies may miss [\u003cspan additionalcitationids=\"CR9\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Evidence from globally diverse settings, including China, Germany, the United States, the Democratic Republic of Congo (DRC), Nigeria, and Cameroon, consistently shows subnational and age-specific variation in seropositivity for poliovirus with implications for micro-planning, catch-up strategies, and the design of outbreak responses [\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eType-specific immunity remains central in the bivalent oral poliovirus vaccine (bOPV) plus inactivated poliovirus vaccine (IPV) era, particularly for poliovirus type-2 following the global switch from tOPV to bOPV in 2016. Studies from Vietnam illustrate the role of IPV in closing the type-2 immunity gaps after the switch, aligning with the needs of programs confronting cVDPV2 risk [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Urban and special-population studies have further demonstrated how local immunization histories, migration, and occupational exposures shape antibody profiles; for example, healthcare professionals in Brazil and newly resettled refugees in Denmark exhibited distinct seroprotection patterns that informed targeted interventions [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. In West and Central Africa, serosurveys conducted among adults and children have provided insights into residual susceptibility in complex delivery environments, thereby informing resource prioritization and guiding the refinement of supplementary immunization activities [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eMethodological considerations are also crucial factors in interpreting seroprevalence. A comparative evaluation of virus-neutralization assays highlights variability across platforms. It underscores the value of harmonization for non-polio enteroviruses, a lesson that translates to poliovirus serology, that host and delivery-system factors, such as seasons of vaccination, prior exposures, and cohort effects, can influence measured antibody levels, reinforcing the need for locally generated estimates rather than reliance on global averages [\u003cspan additionalcitationids=\"CR15 CR16\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Although outside the scope of poliovirus, studies of other vaccine-preventable and viral infections (e.g., varicella disease burden, pertussis, mumps, hepatitis B) and even enterovirus surveillance in animal reservoirs collectively demonstrate how serology guides prevention policy when routine data are insufficient [\u003cspan additionalcitationids=\"CR18 CR19\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn Pakistan, districts categorized as very high-risk districts (VHRDs) concerning polio cases share characteristics commonly observed in other high-risk settings, including population mobility, missed opportunities for routine vaccination, hard-to-reach communities, and a recurrent need for targeted campaigns. In this context, a seroprevalence survey among children in VHRDs was essential to quantify seroprotection against poliovirus types 1, 2, and 3 after years of bOPV/IPV use and targeted responses, as well as risk factors associated with immunity levels. It was also imperative to generate district-level evidence to direct outreach and microplanning. By situating Pakistan\u0026rsquo;s estimates within the context of international experiences, including urban serosurveys, refugee populations, and post-switch evaluations, this study aims to provide decision-oriented immunity maps that support risk-based strategies for the eradication of poliovirus [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eStudy design and participants\u003c/h2\u003e\u003cp\u003eWe conducted a district-specific cross-sectional seroprevalence survey across 44 very high-risk districts of Pakistan, identified by the National Emergency Operation Center (NEOC) due to persistent poliovirus detection in 2022 (Supplementary Table\u0026nbsp;1a). These districts served as geographical strata for this survey. Children were stratified into two age cohorts (6\u0026ndash;11 months and 12\u0026ndash;23 months) and included in the survey.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eSample Size\u003c/h3\u003e\n\u003cp\u003eThe sample size for this survey was calculated based on an assumed true seroprevalence of 90% and a 95% confidence interval with a\u0026thinsp;\u0026plusmn;\u0026thinsp;5% margin of error. A design effect of 1.5 and an anticipated response rate of 90% were considered. This resulted in a required sample size of 210 children per age cohort per stratum (district), totaling 420 children from each district across both age cohorts.\u003c/p\u003e\n\u003ch3\u003eSampling Procedure\u003c/h3\u003e\n\u003cp\u003eTo draw the sample from the target districts, a 1 x 1 km grid was generated over each district using ArcGIS (version 10.2.2). Grids with no residential population were excluded. Only grids with a population greater than 100 and neighboring grids with more than 300 individuals were combined to form the sampling frame. For proportional representation, stratified random sampling was employed at the tehsil (sub-districts) level. In each tehsil, probability proportional to size (PPS) was applied so that grids with larger populations had a higher chance of being selected. A total of 25 clusters were randomly selected per district, with an additional five clusters per district identified as backups. Overall, 1100 clusters were included in the survey design from the 44 target districts, with 125 backup clusters.\u003c/p\u003e\n\u003ch3\u003eData Collection\u003c/h3\u003e\n\u003cp\u003eWeb-based district maps were generated using Google's application programming interfaces (APIs) and uploaded onto handheld devices to guide data collectors. Each map displayed cluster boundaries, cluster extension boundaries, and centroids to ensure accurate navigation to households. Data collection was completed in two phases across the provinces between September 2022 and October 2023. A structured questionnaire was designed to be administered to mothers or caregivers of the target children, collecting information on household demographics and socioeconomic status, as well as child history, including vaccination status, for all children enrolled in the survey. Data on vaccination were recorded from vaccination cards, and in the absence of cards, data were collected through mother/caregiver recall. Along with the data, 2 mL of venous blood was obtained from each child by a trained phlebotomist. During the surveys, households that were locked or those that refused to participate were not replaced with other households.\u003c/p\u003e\u003cp\u003eThe data collection team in the district consisted of two female data collectors, two female phlebotomists, and a male team leader. The team received a comprehensive training, conducted over five days, led by experienced investigators and faculty members from Aga Khan University.\u003c/p\u003e\n\u003ch3\u003eLaboratory methodology\u003c/h3\u003e\n\u003cp\u003eAfter blood collection from a child, each sample was centrifuged, and the serum was isolated and put into sterile, labeled cryovials. The cryovials were stored in a cold box with ice packs and sent immediately to the nearest laboratory collection point of AKU. From these collection points, the samples were transported to the Nutrition Research Laboratory at AKU in Karachi. During the transportation, the temperature of the samples was monitored using a digital thermometer attached to the lid of the ice box. At the laboratory at AKU, two distinct aliquots were prepared; one was kept as a backup, and the other was sent to the National Institute of Health (NIH), Pakistan, for neutralization assay examination [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. For this study, seropositivity was defined as a titer of poliovirus neutralizing antibody greater than 1:8 [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eStatistical analysis\u003c/h2\u003e\u003cp\u003eSeroprevalence was estimated for poliovirus types 1, 2, and 3 by age cohort, child sex, and province. Point estimates were reported at 95% confidence intervals to account for the survey design effect. Immunity gaps were explored by stratifying results by demographic and geographic characteristics.\u003c/p\u003e\u003cp\u003eBivariate analyses were performed to examine the associations between seronegativity and selected covariates, including child age, sex, province of residence, maternal literacy, socioeconomic indicators, and vaccination history, such as receipt of IPV and full immunization status. For categorical variables, the Chi-square test was used with a significance level set at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e\u003cp\u003eMultivariate logistic regression models were fitted to identify independent predictors of seronegativity for each poliovirus type. Adjusted odds ratios (AORs) at 95% CIs were reported. Model specification considered potential confounders identified a priori from the literature, as well as variables significant at p\u0026thinsp;\u0026lt;\u0026thinsp;0.2 in univariate analysis.\u003c/p\u003e\u003cp\u003eSensitivity analyses were performed to assess the robustness of estimates by excluding children with incomplete vaccination histories and stratifying the results by urban\u0026ndash;rural residence. The analysis was conducted using STATA version 18 [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe obtained ethical approval from the Ethical Review Committee of Aga Khan University, Pakistan (2022-7646\u003cstrong\u003e)\u003c/strong\u003e, and the National Bioethics Committee, Pakistan (NBC-814). Informed consent was obtained from the caregivers of the participants included in the study.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eA total of 20,680 children were included (10,112 aged 6-11 months and 10,568 aged 12-23 months); the mean age was 13.5\u0026plusmn;5.3 months (8.9\u0026plusmn;1.7 and 17.9\u0026plusmn;3.5 months for the two cohorts, respectively). Gender distribution was balanced (52.0% male overall; 51.5% and 52.4% in the younger and older cohorts, respectively). \u0026nbsp;Most participants were from Khyber Pakhtunkhwa (KP) (37.0%), followed by Sindh (27.2%), Balochistan (22.4%), Punjab (11.2%), and ICT (2.3%). The provincial distribution was similar across age groups. Over half lived in households with \u0026ge;7 members (53.4% ). Socioeconomic status was evenly distributed across wealth quintiles (~20% in each). Overall, maternal literacy was recorded at 63.7% \u0026nbsp;(Table 1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOf the children included in the survey, 55.2% had received IPV, with a higher proportion of children in the 12-23-month age group than in the 6\u0026ndash;11-month age group (61.3% vs 48.8%, respectively). Altogether, only 31.3% of children received four or more doses of OPV (33.6% of those 12-23 months old and 28.9% in the 6-11 months age group).\u003c/p\u003e\n\u003cp\u003eOverall, 37.2% of children were fully immunized[1], and 44.8% were partially immunized. The proportion of fully immunized children was higher among those in the 6-11 months cohort (42.6%) compared to the 12-23 months cohort (32.0%). A higher proportion of children in the older age cohort were partially immunized (51.1%) compared to those in the younger age cohort (38.2%). District-wise demographic indicators are present in Supplementary Table 1a.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003cstrong\u003e. Demographic indicators, residence, and vaccination history of the study population\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"623\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eTotal\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e6-11 months\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e12-23 months\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eN=20680\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eN=10112\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eN=10568\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eMean age (months)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e13.5 \u0026plusmn; 5.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e8.9 \u0026plusmn; 1.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e17.9 \u0026plusmn; 3.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eGender of Child\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp;Male\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e10,751 (52.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e5,210 (51.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e5,541 (52.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Female\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e9,929 (48.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4,902 (48.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e5,027 (47.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eProvince\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Punjab\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2,307 (11.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1,106 (10.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1,201 (11.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Sindh\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e5,617 (27.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2,739 (27.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2,878 (27.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Balochistan\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4,632 (22.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2,342 (23.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2,290 (21.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp;KPK\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7,654 (37.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3,696 (36.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3,958 (37.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp;ICT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e470 ( 2.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e229 ( 2.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e241 ( 2.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eFamily size\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026lt;7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e9,632 (46.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4,802 (49.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4,830 (50.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026gt;=7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e11,048 (53.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e5,310 (48.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e5,738 (51.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eWealth Quintiles\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Poorest\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4,116 (19.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2,058 (50.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2,058 (50.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp;Poor\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4,143 (20.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2,058 (49.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2,085 (50.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Middle\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4,167 (20.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2,028 (48.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2,139 (51.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp;Rich\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4,132 (20.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1,975 (47.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2,157 (52.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Richest\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4,122 (19.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1,993 (48.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2,129 (51.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eMother education\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Literate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7,513 (36.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3,644 (36.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3,869 (36.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp;Illiterate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e13,167 (63.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e6,468 (64.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e6,699 (63.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eChild ever received IPV\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003eYes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e11,409 (55.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4,936 (48.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e6,473 (61.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003eNo\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e9,271 (44.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e5,176 (51.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4,095 (38.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eTotal OPV doses (RI + SIAs)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp;\u0026lt;4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e14,201 (68.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7,186 (71.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7,015 (66.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp;\u0026gt;=4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e6,479 (31.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2,926 (28.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3,553 (33.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eImmunization status\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp;Not immunized\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3,733 (18.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1,946 (19.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1,787 (16.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Partially immunized\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e9,260 (44.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3,860 (38.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e5,400 (51.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Fully immunized\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7,687 (37.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4,306 (42.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3,381 (32.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eAbbreviations:\u003c/strong\u003e KP: Khyber Pakhtunkhwa; ICT: Islamabad Capital Territory; IPV: Inactivated Poliovirus Vaccine; OPV: Oral Poliovirus Vaccine; RI: Routine Immunization; SIAs: Supplementary Immunization Activities.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSeroprevalence of poliovirus types 1, 2, and 3 by age cohort and province\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOverall, seroprevalence for type 1 was 94.5% (CI: 94 \u0026ndash; 95) and 95.9% (CI: 95.5 \u0026ndash; 96.3) among children 6-11 months and 12-23 months, respectively. The seroprevalence was uniformly high (\u0026gt;94%) across all provinces with minimal age-related differences. On the contrary, type 2 displayed a substantial immunity gap, particularly in younger children, 44.6%(CI: 43.6 \u0026ndash; 45.6), compared to the older age cohort, 53.8% (CI: 52.8 \u0026ndash; 54.8), with the lowest levels in Baluchistan 39% (CI: 37 \u0026ndash; 41) among the younger age cohort, 41.7% \u0026nbsp;(CI: 39.7 \u0026ndash; 43.7) among the older age cohort] and Sindh [37.5% (CI: 35.7 \u0026ndash; 39.3) younger age cohort, and 50% (CI: 48.2 \u0026ndash; 51.8) among older age cohort)]. Districts in Baluchistan and Sindh had low type 2 immunity compared to districts in other provinces (Supplementary Table 1b).\u003c/p\u003e\n\u003cp\u003eThe prevalence of type 3 seroprotection showed intermediate protection, above 90% for all provinces and both age cohorts except in Balochistan [79.5% (95% CI: 77.8 \u0026ndash; 81.2) for younger age cohort] and [82.6% (CI:81.1 \u0026ndash; 84.2) for older age cohort] and in KP for younger age cohort \u0026nbsp;[89.2% (CI: 88.2 \u0026ndash; 90.2 compared to 92.8% (CI: 92.0 \u0026ndash; 93.6)]. Half of the districts in Baluchistan had low type immunity among younger children (Supplementary Table 1b). Overall, protection was stronger for type 1, weaker for type 2, and moderate for type 3, with Baluchistan consistently lagging and ICT maintaining the highest immunity across all serotypes. (Figure. 1).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReverse cumulative distributions of neutralizing antibody titters for poliovirus types 1, 2, 3 by age cohort and province.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe strength of immunity was assessed through the reverse cumulative distribution of neutralizing antibody titers for poliovirus types 1, 2, and 3 in children aged 6-11 months (a, c, e) and 12-23 months (b, d, f) across the provinces (Figure 2). The higher the right-shifted curves, the stronger the immunity. Poliovirus type 1 (PV1) exhibits near-universal, high-titer protection across provinces, with ICT and Punjab showing the highest titters and Baluchistan the lowest; older children have slightly higher titters. Poliovirus type 2 (PV2) exhibits the weakest immunity, with a steep drop in titters after reaching low levels, highlighting significant gaps in Baluchistan and Sindh. In contrast, ICT and KP show comparatively better results, with older children again displaying modestly higher titters. Poliovirus type 3 (PPV3) lies between PV1 and PV2, offering generally strong protection but lower than PV1, and Baluchistan consistently lags behind. Overall, the figure demonstrates robust PV1 and PV3 immunity, but persistent gaps in PV2 immunity, especially among younger children and in Sindh and Balochistan.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRisk factors associated with poliovirus seronegativity: Univariate and multivariate analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe assessed risk factors associated with poliovirus seroprevalence using the univariate and multivariate models. Sero-negativity was highest in Baluchistan (8.0%) and KP (3.0%) compared to Punjab (1.1%), Sindh (1.7%), and ICT (0.9%). \u0026nbsp;In the adjusted model, children from Baluchistan have significantly lower odds of seropositivity (AOR 0.178, CI: 0.066 - 0.484; p\u0026lt;0.001). A nonlinear association was found between household wealth and level of seroprotection, with nonsignificant differences between the poorest and richest groups (AOR 1.105, 95% CI: 0.816 \u0026ndash; 1.496, p = 0.520). Children in the older age cohort were more likely to be seroprotected compared to the younger age cohort (AOR 1.356, 95% CI: 1.161 \u0026ndash; 1.583, p\u0026lt;0.001). Also, receiving \u0026lt;4 doses of OPV had 1.2 times higher odds of seroprotection (AOR 1.25, 95% CI: 1.021 \u0026ndash; 1.529, p\u0026lt;0.030) compared to receiving \u0026nbsp;\u0026gt;= 4 doses (Table 2).\u003c/p\u003e\n\u003cp\u003eA clear association was observed between immunization and immunity level: non-immunized children had the highest sero-negativity (7.8%), partially immunized children showed relatively higher protection (AOR 3.846, CI: 2.99 \u0026ndash; 4.947; p \u0026lt; 0.001), while being fully immunized was significantly associated with higher seroprotection. A fully immunized child is 2 times more protected compared to a non-immunized child (AOR 2.004, 95% CI: 1.643 \u0026ndash; 2.444, p\u0026lt;0.001).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2. Univariate and Multivariate Analysis for Risk Factors Associated with Seroprevalence\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"627\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eUnadjusted Odds\u003cbr\u003e\u0026nbsp;Ratio for\u003cbr\u003e\u0026nbsp;Seropositivity\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eP-values\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eAdjusted Odds Ratio\u003cbr\u003e\u0026nbsp;for Seropositivity\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eP-values\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"bottom\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eAny Type Poliovirus\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eSeronegative\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eSeropositive\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eN=708\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eN=19,409\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eProvince\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Punjab\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e24 ( 1.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2,231 (98.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.861 (0.297,2.493)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.782\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.695 (0.238,2.026)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.505\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Sindh\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e94 ( 1.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e5,414 (98.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.533 (0.195,1.458)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.220\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.668 (0.243,1.835)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.433\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Balochistan\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e362 ( 8.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4,138 (92.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.106 (0.039,0.285)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.178 (0.066,0.484)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; KPK\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e224 ( 3.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7,194 (97.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.297 (0.110,0.803)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.017\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.415 (0.153,1.127)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.084\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; ICT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4 ( 0.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e432 (99.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRef.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRef.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eFamily size\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026lt;7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e253 ( 2.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e9,120 (97.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRef.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026gt;=7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e455 ( 4.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e10,289 (95.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.627 (0.537,0.733)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eWealth Quintiles\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Poorest\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e146 ( 3.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3,884 (96.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRef.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRef.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Poor\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e169 ( 4.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3,888 (95.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.865 (0.690,1.084)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.207\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.885 (0.702,1.116)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.302\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Middle\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e186 ( 4.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3,850 (95.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.778 (0.624,0.971)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.026\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.679 (0.54,0.854)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Rich\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e136 ( 3.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3,876 (96.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.071 (0.845,1.359)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.570\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.74 (0.579,0.946)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e0.016\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Richest\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e71 ( 1.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3,911 (98.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2.071 (1.554,2.759)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.105 (0.816,1.496)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.520\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eMother education\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Literate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e158 ( 2.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7,148 (97.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2.029 (1.696,2.428)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Illiterate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e550 ( 4.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e12,261 (95.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRef.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eSex of Child\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Male\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e357 ( 3.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e10,079 (96.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.062 (0.914,1.234)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.431\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Female\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e351 ( 3.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e9,330 (96.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRef.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eChild age\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; 6-11 months\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e409 ( 4.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e9,377 (95.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRef.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRef.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; 12-23 months\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e299 ( 2.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e10,032 (97.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.463 (1.257,1.703)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.356 (1.161,1.583)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eChild ever received IPV\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp;Yes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e230 ( 2.1%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e10,892 (97.9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRef.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; No\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e478 ( 5.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e8,517 (94.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.376 (0.321,0.441)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eTotal OPV doses (RI + SIAs)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp;\u0026lt;4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e505 ( 3.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e13,328 (96.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.881 (0.747,1.040)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.25 (1.021,1.529)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e0.030\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp;\u0026gt;=4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e203 ( 3.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e6,081 (96.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRef.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRef.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eImmunization status\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Not immunized\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e280 ( 7.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3,312 (92.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRef.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRef.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Partially immunized\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e146 ( 1.6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e8,884 (98.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e5.144 (4.195,6.309)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.846 (2.99,4.947)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; Fully immunized\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e282 ( 3.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7,213 (96.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2.162 (1.824,2.564)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2.004 (1.643,2.444)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026lt;0.001\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e[1] A child was categorized as fully immunized when s/he completed vaccination from birth through the first dose of measles-containing vaccine (MCV1), which is scheduled to be given at nine months of age as per the Expanded Program on Immunization (EPI), Pakistan, \u0026nbsp;i.e., BCG, OPV0, OPV1-3, Penta1-3, PCV1-3, IPV, and MCV1. This definition excludes Hep-B at birth, ROTA 1at six weeks, ROTA 2 at ten weeks, and TCV at nine months.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis seroprevalence survey, conducted in 44 very high-risk districts of Pakistan, provides one of the most granular assessments of poliovirus immunity among children in recent years. Our results showed that overall population-level immunity remains high for the type I strain, with more than 94% of children showing serological evidence of protection. However, significant variability in immunity levels persists across age groups and regions, and immunity gaps exist for virus types 2 and 3, similar to patterns observed in other endemic regions. The findings highlight both the progress made and the fragility of eradication efforts, especially regarding poliovirus types 2 and 3 among the target age groups.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOur results for type 1 are consistent with findings from other studies in diverse settings. An Afghan serological survey conducted in 2017 also recorded similarly high type 1 immunity in children under two years of age [25]. Additionally, in India, seroprotection for type 1 polio was over 95% in Uttar Pradesh – a polio high-risk region - before the disruption of wild poliovirus transmission [26]. Likewise, in West Africa, serosurveys in Nigeria and Chad also observed greater protection against type 1 in zones where intensive SIAs were conducted [27, 28]. These convergent findings suggest that, despite operational weaknesses, frequent OPV exposure has been sufficient to maintain high immunity against type 1 in various settings.\u003c/p\u003e\n\u003cp\u003eConversely, our findings of low immunity level for the type 2 strain reflect the global consequence of the tOPV withdrawal in 2016. In the post-switch period, type 2 seroprevalence in Pakistan declined below 50% among children under two years, especially in children with low IPV coverage [3]. A multi-country analysis of poliovirus immunity levels reported that type 2 immunity declined steeply two to three years after the global post-switch, particularly in regions with suboptimal IPV coverage [29]. A similar trend was reported in Nigeria, where type 2 population immunity decreased after the transition, leading to recurrent outbreaks of circulating vaccine-derived poliovirus type 2 (cVDPV2) [30]. A study from Syria showed that large cVDPV2 outbreaks after tOPV withdrawal unveiled immunity gaps among children under two years of age, via low IPV uptake and immunization disruption due to conflict [31].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOur reverse cumulative titer curves for type 2 immunity showed that protection in the target regions is weak in strength and low in coverage, with much lower median titers. The results are consistent with known immunological limitations of \u0026nbsp;IPV, which induces predominantly systemic humoral responses but fails to induce lasting mucosal immunity. Findings from a randomized controlled trial in India indicated that a single dose of IPV is sufficient to enhance type 2 immunity. Still, restoration of population immunity is only with increasing coverage and, in specific settings, targeted use of monovalent OPV (mOPV) [32]. The low median titers in our study, particularly in more classically high-risk settings, suggest that, apart from IPV's general failure to elicit intestinal immunity, systemic immunity per se is similarly suboptimal in such groups, presumably due to an incompletely vaccinated population, missed doses, or loss of antibody. Combined, these double vulnerabilities underscore the heightened risk of children in such settings being exposed to poliovirus circulation.\u003c/p\u003e\n\u003cp\u003eSeroprotection against poliovirus type 3 in our study was lower compared to the level of immunity level, and showed extensive provincial variation, with the lowest rates in Baluchistan. This finding is consistent with global evidence that type 3 immunity lags type 1, even in countries with higher routine immunization coverage. The Type 3 component of OPV is less immunogenic than the Type 1 component, and seroconversion requires multiple doses. In India and Pakistan, type 3 seroprevalence generally lagged behind type 1 by 5–10 percentage points, both due to its diminished immunogenicity and irregular SIA quality [26]. These disparities have also been observed in Nigeria and South Africa, where type 3 immunity consistently fell below the level required to break transmission [27, 33]. Comparisons highlight that type 3 is an ongoing issue across the world, where not only routine vaccination but also high-quality SIAs are required in low coverage pockets of the population.\u003c/p\u003e\n\u003cp\u003eThe gradient of age in our findings, with older children aged 12–23 months having higher immunity to all serotypes, reflects cumulative exposure from routine immunization and campaigns. Such age effects have been observed earlier in India, Nigeria, and Afghanistan, where younger children typically exhibit lower seroprevalence until more doses of OPV are administered [27, 34, 35]. Similarly, cross-sectional studies in China and Cameroon have also reported the same trends [10, 12]. Also, Pakistan-specific studies have consistently demonstrated similar trends [36,37]. The continuity of these trends at the regional levels is a sign of missed opportunities during the first year of life, reflecting gaps in routine immunization, integration of services with maternal and child health, and the effectiveness of SIAs. They emphasize the need for effective and timely routine immunization to fill immunity gaps among the most vulnerable age groups.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOur analysis identifies key demographic and programmatic factors influencing poliovirus seroprevalence in Pakistan. Geographic inequity was evident in Balochistan, whereby children had significantly lower odds of seropositivity compared with other provinces, even after adjusting for confounding factors. This finding aligns with sustained concerns about programmatic challenges in Balochistan, including security-related restrictions, weak health infrastructure, and widespread population mobility. These geographic variations in immunity have also been reported in northern Nigeria and Afghanistan, where ongoing reservoirs of incompletely immunized children have caused poliovirus transmission despite very high immunization coverage at the national level [34, 35].\u003c/p\u003e\n\u003cp\u003eMaternal literacy was highly correlated with seroprotection in our unadjusted model, and mothers whose children were literate were likely to be tested seropositive. This finding aligns with earlier studies conducted in Pakistan and other low- and middle-income countries, which have demonstrated that caregiver education improves health-seeking behavior and vaccine coverage [34, 35, 38]. While attenuated in the adjusted model, the direction of the association serves to emphasize the continued influence of social determinants on immunity outcomes.\u003c/p\u003e\n\u003cp\u003eHousehold wealth had a nonlinear effect on seroprotection level in our study. Children in the wealthiest quintile had no appreciably greater odds of seropositivity compared to those in the poorest quintile. However, those in the more affluent and intermediate quintiles had decreased odds. The contradictory trends are hypothesized to indicate that the economic slopes of immunity to polio might be more complex than those for other childhood vaccines, perhaps because of the widespread use of mass campaigns that span socioeconomic lines. However, data from international eradication contexts indicate that socioeconomic disadvantage remains a persistent risk factor for underimmunization, particularly in areas where routine service availability is limited [27, 34, 35].\u003c/p\u003e\n\u003cp\u003eVaccination history was one of the major predictors of seroprotection. Children who were not immunized were most seronegative, whereas partially and fully immunized children had significantly higher odds of being seropositive, indicating the direct effect of full immunization on immunity. Similar findings were reported in a study from Nigeria, where missing doses or incomplete doses were the most persistent predictors of susceptibility [27]. Contrary to previous studies, our analysis revealed that children who reported receiving fewer than four doses of OPV had marginally higher adjusted odds of seropositivity compared to those who received four or more doses [36, 39]. This seeming paradox may have occurred due to parental recall bias, misclassification of vaccine doses during recall, or differential campaign performance, where fewer but more intense exposures were administered. This inconsistency needs closer attention, most importantly by validation of vaccination history against independent records.\u003c/p\u003e\n\u003cp\u003eTogether, these results show that a dynamic interplay of geographic, demographic, and programmatic factors shapes Pakistan's poliovirus immunity. Structural disparities, the impact of maternal education, and the priority of universal immunization all make it clear that eradication is both a social and biomedical challenge. Continued progress will entail not just high rates of coverage through routine and supplemental campaigns but also interventions aimed at eliminating regional and social disparities that continue to propel transmission.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis study is not without limitations. Its cross-sectional nature constrains causal inferences from individual-level changes in immunity. The history of vaccination was partially ascertained by caregiver report in the absence of vaccination cards. This is likely to result in the unintentional recall bias for vaccination status. Neutralizing antibody titers are a measurement of humoral immunity. Still, they will not necessarily capture mucosal immunity that is essential for breaking the transmission of poliovirus, especially when using the oral polio vaccine. Contextual factors, such as seasonal migration, access issues, and overlapping supplementary immunization activities during the survey period, could have affected both vaccination exposure and seroprevalence measured, possibly limiting generalizability.\u003c/p\u003e\n\u003cp\u003eDespite this, our findings reveal prevalence and inequalities in poliovirus immunity in high-risk regions of Pakistan, providing evidence for targeted programmatic interventions.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eOur findings underscore the necessity of addressing immunity gaps in types 2 and 3 in Pakistan's polio program, especially for younger children in the high-risk areas. Enhancing the' quality and reach of OPV campaigns, expanding IPV coverage, and integrating immunization with maternal and child health services are crucial for ensuring protection in the early years of life. Simultaneously addressing vaccine hesitancy and building trust through sustained community involvement would help to strengthen the approach towards poliovirus eradication in the country.\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions:\u0026nbsp;\u003c/strong\u003eSBS conceptualized and designed the survey and assisted with interpreting the results. IH developed the sampling strategy and tools and supervised the field activities. AK, AH and MU jointly drafted the manuscript. MU assisted with study design, formulating contextually relevant survey tools, and oversaw data collection activity. MS performed the statistical analysis. MMA supervised the laboratory analysis of the samples. MAH, AB, RH, JF, and all authors reviewed and approved the final manuscript for submission.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest:\u0026nbsp;\u003c/strong\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability:\u003c/strong\u003e The data will be made available upon request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgment:\u0026nbsp;\u003c/strong\u003eWe are immensely grateful to all participants for their cooperation during the survey.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding sources:\u003c/strong\u003eThe study was supported by the Bill \u0026amp; Melinda Gates Foundation [grant number OPP1156736].\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWorld Health Organization. Two out of three wild poliovirus strains have been eradicated. Accessed September 07, 2025. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.who.int/news-room/feature-stories/detail/two-out-of-three-wild-poliovirus-strains-eradicated\u003c/span\u003e\u003cspan address=\"https://www.who.int/news-room/feature-stories/detail/two-out-of-three-wild-poliovirus-strains-eradicated\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGlobal Polio Eradication Initiative (GPEI). Global eradication of wild poliovirus type 2 declared - GPEI. Accessed September 07, 2025. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://polioeradication.org/news/global-eradication-of-wild-poliovirus-type-2-declared/\u003c/span\u003e\u003cspan address=\"https://polioeradication.org/news/global-eradication-of-wild-poliovirus-type-2-declared/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHussain I, Umer M, Khan A, Sajid M, Ahmed I, Begum K, Iqbal J, Alam MM, Safdar RM, Baig S, Voorman A, Partridge J, and Soofi S (2024). Exploring the path to polio eradication: insights from consecutive seroprevalence surveys among Pakistani children. Front. Public Health 12:1384410. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3389/fpubh.2024.1384410\u003c/span\u003e\u003cspan address=\"10.3389/fpubh.2024.1384410\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePolio cases in Pakistan | District-wise. Accessed September 07, 2025. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.endpolio.com.pk/polioin-pakistan/district-wise-polio-cases\u003c/span\u003e\u003cspan address=\"https://www.endpolio.com.pk/polioin-pakistan/district-wise-polio-cases\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAlfonso VH, Voorman A, Hoff NA, et al. Poliovirus immunity among adults in the Democratic Republic of the Congo: a cross-sectional serosurvey. BMC Infect Dis. 2022;22(1):30. doi:\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1186/s12879-021-06951-6\u003c/span\u003e\u003cspan address=\"10.1186/s12879-021-06951-6\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKohmer N, Rabenau HF, Rilling V, Ciesek S, Enders M, Eggers M. Polio type 2 and 3 eradication: Relevance to the immunity status of individuals living in Germany, 2005\u0026ndash;2020. J Clin Virol. 2023;164:105471. doi:\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.jcv.2023.105471\u003c/span\u003e\u003cspan address=\"10.1016/j.jcv.2023.105471\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWallace, G.S., Curns, A.T., Weldon, W.C. et al. Seroprevalence of Poliovirus Antibodies in the United States Population, 2009\u0026ndash;2010. BMC Public Health 16, 721 (2016). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1186/s12889-016-3386-1\u003c/span\u003e\u003cspan address=\"10.1186/s12889-016-3386-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHvass AMF, Wejse C. High coverage of polio immunization program in refugees resettling in Denmark. A cross-sectional study of polio serology in newly arrived refugees. Expert Rev Vaccines. 2019;18(12):1317\u0026ndash;1322. doi: 10.1080/14760584.2019.1698953. Epub 2019 Dec 10. PMID: 31771367.H\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMoraes JC, Rujula MJP, Otsuka M. Prevalence of Neutralizing Antibodies Against Poliovirus 1, 2, and 3 in healthcare professionals aged 20\u0026ndash;50 years. Rev Paul Pediatr. 2021;39:e2019354. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1590/1984-0462/2021/39/2019354\u003c/span\u003e\u003cspan address=\"10.1590/1984-0462/2021/39/2019354\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eXu J, Kuang S, Rong R, Zhang Y, Tang W, Wang Q. Sero-survey of polio antibodies and quality of acute flaccid paralysis surveillance in Chongqing, China: A cross-sectional study. Medicine (Baltimore). 2020;99(31):e21298. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1097/MD.0000000000021298\u003c/span\u003e\u003cspan address=\"10.1097/MD.0000000000021298\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBolu O, Adamu U, Franka R, Umeokonkwo CD, An Q, Greby S, McDonald S, Mainou B, Mba N, Agala N, Archer WR, Braka F, Etapelong SG, Gashu TS, Siddique AR, Asekun A, Okoye M, Iriemenam N, Wiesen E, Swaminathan M, Ihekweazu C, Shuaib F. Seroprevalence of poliovirus antibodies in Nigeria: refining strategies to sustain the eradication effort. Pan Afr Med J. 2023;45(Suppl 2):2. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.11604/pamj.supp.2023.45.2.38098.\u003c/span\u003e\u003cspan address=\"10.11604/pamj.supp.2023.45.2.38098.\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eClaire Endegue M, Sein C, Lopez Cavestany R, Jeyaseelan V, Palmer T, Norbert Soke G, Diaha A, Jafri B, Mainou BA, Verma H, Mach O. Community-based survey to assess seroprevalence of poliovirus antibodies in far-north Cameroon in 2020. Vaccine X. 2022;12:100244. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.jvacx.2022.100244.C\u003c/span\u003e\u003cspan address=\"10.1016/j.jvacx.2022.100244.C\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHuyen DTT, Mach O, Thanh Trung N, Thai PQ, Thang HV, Weldon WC, Oberste MS, Jeyaseelan V, Sutter RW, Anh DD. Rapid Disappearance of Poliovirus Type 2 (PV2) Immunity in Young Children Following Withdrawal of Oral PV2-Containing Vaccine in Vietnam. J Infect Dis. 2019;220(3):386\u0026ndash;391. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1093/infdis/jiz124\u003c/span\u003e\u003cspan address=\"10.1093/infdis/jiz124\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAbreu TC, Boshuizen H, Mollema L, Berbers GAM, Korthals Altes H. Association between season of vaccination and antibody levels against infectious diseases. Epidemiol Infect. 2020;148:e276. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1017/S0950268820002691\u003c/span\u003e\u003cspan address=\"10.1017/S0950268820002691\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKarelehto E, Koen G, Benschop K, van der Klis F, Pajkrt D, Wolthers K. Enterovirus D68 serosurvey: evidence for endemic circulation in the Netherlands, 2006 to 2016. Euro Surveill. 2019;24(35):1800671. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.2807/1560-7917.ES.2019.24.35.1800671\u003c/span\u003e\u003cspan address=\"10.2807/1560-7917.ES.2019.24.35.1800671\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang J, Wu W, Wang W, Zhang J, Xiao J, Cai M, Guo J, Li R, Zhu S, Zhang W, Chen M, Teng Z. Seroprevalence of neutralizing antibodies against HFMD associated enteroviruses among healthy individuals in Shanghai, China, 2022. Virol Sin. 2024;39(4):694\u0026ndash;698. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.virs.2024.05.008\u003c/span\u003e\u003cspan address=\"10.1016/j.virs.2024.05.008\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDoshi RH, Alfonso VH, Hoff NA, Mukadi P, Gerber S, Bwaka A, Higgins SG, Mwamba GN, Okitolonda E, Muyembe JJ, Rimoin AW. Evidence of Mumps Infection Among Children in the Democratic Republic of Congo. Pediatr Infect Dis J. 2017;36(5):462\u0026ndash;466. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1097/INF.0000000000001483\u003c/span\u003e\u003cspan address=\"10.1097/INF.0000000000001483\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSytiuk MP, Bezymennyy MV, Halka IV, Uhovskyy VV, Muzykina LM, Lavalley M, Nychyk SA, Nedosekov VV, Howard MW, Bortz E. Seroprevalence of Enzootic Teschen Disease in the Wild Boar Population in Ukraine. Vector Borne Zoonotic Dis. 2022;22(2):138\u0026ndash;147. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1089/vbz.2021.0063.Syt\u003c/span\u003e\u003cspan address=\"10.1089/vbz.2021.0063.Syt\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eUmego CF, Mboto CI, Asitok AD, Osaji LC, George UE, Edet UO, Mbim EN, Faleye TO, Adewumi OM, Adeniji JA. Circulation of hepatitis B virus genotype-E among outpatients in tertiary hospitals in the Niger-Delta region of Nigeria. Afr Health Sci. 2022;22(1):511\u0026ndash;520. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.4314/ahs.v22i1.60\u003c/span\u003e\u003cspan address=\"10.4314/ahs.v22i1.60\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVan Lier A, de Gier B, McDonald SA, Mangen MJ, van Wijhe M, Sanders EAM, Kretzschmar ME, van Vliet H, de Melker HE. Disease burden of varicella versus other vaccine-preventable diseases before introduction of vaccination into the national immunisation programme in the Netherlands. Euro Surveill. 2019;24(18):1800363. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.2807/1560-7917.ES.2019.24.18.1800363\u003c/span\u003e\u003cspan address=\"10.2807/1560-7917.ES.2019.24.18.1800363\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCouder\u0026eacute; K, Benschop KSM, Koen G, van Eijk H, Harvala H, Bailly JL,et al. Assessment of twelve echovirus virus-neutralisation assays in Europe: recommendations for harmonisation of non-polio enterovirus sero-surveillance studies. J Gen Virol. 2024;105(9). doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1099/jgv.0.001986\u003c/span\u003e\u003cspan address=\"10.1099/jgv.0.001986\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWeldon WC, Oberste MS, MA P. Standardized methods for detection of poliovirus antibodies. New York: Springer (2016).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePlotkin SA. Correlates of protection induced by vaccination. Clin Vaccine Immunol. (2010) 17:1055\u0026ndash;65. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1128/CVI.00131-10\u003c/span\u003e\u003cspan address=\"10.1128/CVI.00131-10\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eStataCorp. Stata Statistical Software: Release 17. College Station, TX: StataCorp LLC.; 2025.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHussain I, Mach O, Hamid NA, Bhatti ZS, Moore DD, Oberste MS, Khan S, Khan H, Weldon WC, Sutter RW, Bhutta ZA, Soofi SB. Seroprevalence of anti-polio antibodies in children from polio high risk area of Afghanistan: A cross sectional survey 2017. Vaccine. 2018;36(15):1921\u0026ndash;1924. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.vaccine.2018.02.055\u003c/span\u003e\u003cspan address=\"10.1016/j.vaccine.2018.02.055\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSunil Bahl, Howard E. Gary, Hamid Jafari, Bidyut K. Sarkar, Surendra K. Pathyarch, Raman Sethi, Jagadish Deshpande, An Acute Flaccid Paralysis Surveillance\u0026ndash;Based Serosurvey of Poliovirus Antibodies in Western Uttar Pradesh, India, The Journal of Infectious Diseases, Volume 210, Issue suppl_1, November 2014, Pages S234\u0026ndash;S242, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1093/infdis/jiu379\u003c/span\u003e\u003cspan address=\"10.1093/infdis/jiu379\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eEtsano A, Damisa E, Shuaib F, Nganda GW, Enemaku O, Usman S, Adeniji A, Jorba J, Iber J, Ohuabunwo C, Nnadi C, Wiesen E. Environmental Isolation of Circulating Vaccine-Derived Poliovirus After Interruption of Wild Poliovirus Transmission - Nigeria, 2016. MMWR Morb Mortal Wkly Rep. 2016;65(30):770\u0026ndash;3. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.15585/mmwr.mm6530a4\u003c/span\u003e\u003cspan address=\"10.15585/mmwr.mm6530a4\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGamougam K, Jeyaseelan V, Jones KAV, Mainou BA, Palmer T, Diaha A, Wiesen E, Ntezayabo B, Ayangma R, Soke NG, Samba D, Okiror S, Mach O. A Survey to Assess Serological Prevalence of Poliovirus Antibodies in Areas With High-Risk for Vaccine-Derived Poliovirus Transmission in Chad. J Pediatric Infect Dis Soc. 2022;11(2):55\u0026ndash;59. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1093/jpids/piab103\u003c/span\u003e\u003cspan address=\"10.1093/jpids/piab103\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. PMID: 34791366; PMCID: PMC8865003.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVoorman A, Lyons H, Bennette C, Kovacs S, Makam JK, F Vertefeuille J, Tallis G. Analysis of population immunity to poliovirus following cessation of trivalent oral polio vaccine. Vaccine. 2023;41 Suppl 1(Suppl 1):A85-A92. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.vaccine.2022.03.013\u003c/span\u003e\u003cspan address=\"10.1016/j.vaccine.2022.03.013\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBurns CC, Shaw J, Jorba J, Bukbuk D, Adu F, Gumede N, Pate MA, Abanida EA, Gasasira A, Iber J, Chen Q, Vincent A, Chenoweth P, Henderson E, Wannemuehler K, Naeem A, Umami RN, Nishimura Y, Shimizu H, Baba M, Adeniji A, Williams AJ, Kilpatrick DR, Oberste MS, Wassilak SG, Tomori O, Pallansch MA, Kew O. Multiple independent emergences of type 2 vaccine-derived polioviruses during a large outbreak in northern Nigeria. J Virol. 2013;87(9):4907\u0026ndash;22. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1128/JVI.02954-12\u003c/span\u003e\u003cspan address=\"10.1128/JVI.02954-12\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMbaeyi C, Moran T, Wadood Z, Ather F, Sykes E, Nikulin J, Al Safadi M, Stehling-Ariza T, Zomahoun L, Ismaili A, Abourshaid N, Asghar H, Korukluoglu G, Duizer E, Ehrhardt D, Burns CC, Sharaf M. Stopping a polio outbreak in the midst of war: Lessons from Syria. Vaccine. 2021;39(28):3717\u0026ndash;3723. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.vaccine.2021.05.045\u003c/span\u003e\u003cspan address=\"10.1016/j.vaccine.2021.05.045\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAhmad M, Verma H, Deshpande J, Kunwar A, Bavdekar A, Mahantashetti NS, Krishnamurthy B, Jain M, Mathew MA, Pawar SD, Sharma DK, Sethi R, Visalakshi J, Mohanty L, Bahl S, Haldar P, Sutter RW. Immunogenicity of Fractional Dose Inactivated Poliovirus Vaccine in India. J Pediatric Infect Dis Soc. 2022;11(2):60\u0026ndash;68.). doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1093/jpids/piab091\u003c/span\u003e\u003cspan address=\"10.1093/jpids/piab091\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBrown L, Bingham J, Pulliam J, Mthombothi Z, Sereo T, Kamupira M, Botha S, Molema K, Maseti E, Sch\u0026ouml;nfeldt M, Mabhena N, Prabdial-Sing N, von Gottberg A, McCarthy K, van Schalkwyk C. Estimation of the poliovirus type 2 immunity gap in South Africa. Vaccine. 2024;42(23):126062. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.vaccine.2024.06.029\u003c/span\u003e\u003cspan address=\"10.1016/j.vaccine.2024.06.029\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOdusanya, O.O., Alufohai, E.F., Meurice, F.P. et al. Determinants of vaccination coverage in rural Nigeria. BMC Public Health 8, 381 (2008). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1186/1471-2458-8-381\u003c/span\u003e\u003cspan address=\"10.1186/1471-2458-8-381\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAalemi AK, Shahpar K, Mubarak MY. Factors influencing vaccination coverage among children age 12\u0026ndash;23 months in Afghanistan: Analysis of the 2015 Demographic and Health Survey. PLoS One. 2020;15(8):e0236955. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1371/journal.pone.0236955\u003c/span\u003e\u003cspan address=\"10.1371/journal.pone.0236955\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHussain I, Mach O, Habib A, Bhatti Z, Suhag Z, Oberste MS, Weldon WC, Sutter RW, Soofi SB, Bhutta ZA. Seroprevalence of Anti-polio Antibodies in Children From Polio High-risk Areas of Pakistan: A Cross-Sectional Survey 2015\u0026ndash;2016. Pediatr Infect Dis J. 2017;36(9):e230-e236. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1097/INF.0000000000001622\u003c/span\u003e\u003cspan address=\"10.1097/INF.0000000000001622\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSodhar IA, Mehraj J, Hussaini AS, Aamir M, Mahsaud J, Ahmed S, Shaikh AA, Zardari AA, Rasool S, Chandio SA, Stuckey EM. Population Movement and Poliovirus Spread across Pakistan and Afghanistan in 2023. Vaccines (Basel). 2024;12(9):1006. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3390/vaccines12091006\u003c/span\u003e\u003cspan address=\"10.3390/vaccines12091006\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHabib M, Soofi S, Ali N, Sutter RW, Palansch M, Qureshi H, Akhtar T, Molodecky NA, Okayasu H, Bhutta ZA. A study evaluating poliovirus antibodies and risk factors associated with polio seropositivity in low socioeconomic areas of Pakistan. Vaccine. 2013;31(15):1987\u0026ndash;93. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.vaccine.2013.02.003\u003c/span\u003e\u003cspan address=\"10.1016/j.vaccine.2013.02.003\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eIliyasu Z, Verma H, Craig KT, Nwaze E, Ahmad-Shehu A, Jibir BW, Gwarzo GD, Gajida AU, Weldon WC, Steven Oberste M, Takane M, Mkanda P, Muhammad AJG, Sutter RW. Poliovirus seroprevalence before and after interruption of poliovirus transmission in Kano State, Nigeria. Vaccine. 2016;34(42):5125\u0026ndash;5131. doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.vaccine.2016.08.058\u003c/span\u003e\u003cspan address=\"10.1016/j.vaccine.2016.08.058\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"npj-vaccines","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"npjvaccines","sideBox":"Learn more about [npj Vaccines](http://www.nature.com/npjvaccines/)","snPcode":"41541","submissionUrl":"https://submission.springernature.com/new-submission/41541/3?","title":"npj Vaccines","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"NPJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Poliovirus seroprevalence, children aged 6–23 months, immunity gaps, polio high-risk districts, Pakistan","lastPublishedDoi":"10.21203/rs.3.rs-7664228/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7664228/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWild poliovirus remains endemic in Pakistan and Afghanistan despite global progress. We quantified immunity to poliovirus types 1\u0026ndash;3 among children aged 6\u0026ndash;23 months in 44 high-risk districts (2022\u0026ndash;2023) using a cross-sectional serosurvey with PPS cluster sampling. We enrolled 20,680 children (10,112 aged 6\u0026ndash;11 months; 10,568 aged 12\u0026ndash;23 months). Seroprevalence among 6\u0026ndash;11-month-olds was 94.5% (type 1), 44.6% (type 2), and 88.0% (type 3); among 12\u0026ndash;23-month-olds. It was 95.9%, 53.8%, and 91.2%, respectively. Type 1 seropositivity was highest across provinces; type 3 exceeded 90% except in Balochistan and KP; type 2 was lowest everywhere. Younger children have lower immunity. In multivariable models, residence in Balochistan predicted reduced seroprotection (AOR 0.178, 95% CI 0.066\u0026ndash;0.484); older age (AOR 1.356, 1.161\u0026ndash;1.583) and full immunization (AOR 2.004, 1.643\u0026ndash;2.444) increased odds; \u0026lt;4 OPV doses showed higher odds (AOR 1.25, 1.021\u0026ndash;1.529). Wealth showed a non-linear association. Gaps in types 2\u0026ndash;3 warrant stronger RI, expanded IPV, and tailored SIAs.\u003c/p\u003e","manuscriptTitle":"Progress and gaps in poliovirus immunity: Evidence from a serological survey of children aged 6-23 months in high-risk districts of Pakistan","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-20 08:42:07","doi":"10.21203/rs.3.rs-7664228/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-11-04T14:41:24+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-23T21:01:19+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-16T14:41:32+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-15T11:22:02+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"88072744845963286219236952903408952440","date":"2025-10-14T15:20:11+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"66528074802896865580561609879879065183","date":"2025-10-13T09:50:23+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"1583489744997200276569080690316091437","date":"2025-10-13T05:42:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"293615230165686604908567759888388899748","date":"2025-10-08T17:39:56+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-10-07T15:24:13+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-10-07T14:06:16+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-09-30T09:10:11+00:00","index":"","fulltext":""},{"type":"submitted","content":"npj Vaccines","date":"2025-09-20T10:06:51+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"npj-vaccines","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"npjvaccines","sideBox":"Learn more about [npj Vaccines](http://www.nature.com/npjvaccines/)","snPcode":"41541","submissionUrl":"https://submission.springernature.com/new-submission/41541/3?","title":"npj Vaccines","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"NPJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"50a4ade8-a761-453f-987c-d0acadddbe75","owner":[],"postedDate":"October 20th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":56524250,"name":"Health sciences/Diseases"},{"id":56524251,"name":"Health sciences/Health care"},{"id":56524252,"name":"Biological sciences/Immunology"},{"id":56524253,"name":"Health sciences/Medical research"},{"id":56524254,"name":"Biological sciences/Microbiology"}],"tags":[],"updatedAt":"2026-01-05T15:59:34+00:00","versionOfRecord":{"articleIdentity":"rs-7664228","link":"https://doi.org/10.1038/s41541-025-01352-1","journal":{"identity":"npj-vaccines","isVorOnly":false,"title":"npj Vaccines"},"publishedOn":"2025-12-30 15:57:23","publishedOnDateReadable":"December 30th, 2025"},"versionCreatedAt":"2025-10-20 08:42:07","video":"","vorDoi":"10.1038/s41541-025-01352-1","vorDoiUrl":"https://doi.org/10.1038/s41541-025-01352-1","workflowStages":[]},"version":"v1","identity":"rs-7664228","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7664228","identity":"rs-7664228","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}