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

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.