biostudies-literatureHussain IBill and Melinda Gates Foundation31https://www.ebi.ac.uk/biostudies/studies/S-EPMC12852092biostudies-literatureUnknown11(1)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 probability proportional to size (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 (AORNPJ vaccinesProgress and gaps in poliovirus immunity: Evidence from a serological survey of children aged 6-23 months in high-risk districts of Pakistan.PMC12852092OPP1156736Alam MMPartridge JSoofi SBosan AHafiz RSajid MHussain IKhan AUmer MAbbas HHaq MAfalseProgress and gaps in poliovirus immunity: Evidence from a serological survey of children aged 6-23 months in high-risk districts of Pakistan.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 probability proportional to size (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 (AOR2025-01-01T00:00:00Z2025 Dec2026-06-12T10:19:04.993Z2026-06-12T03:11:39.73ZS-EPMC128520924146940010.1038/s41541-025-01352-1