@article{Gray:2026,
author = {Gray, E and Cooper, L and Ramirez, Gonzalez A and Mach, O and Derqui, N and Grassly, N and Blake, I},
journal = {PLoS Medicine},
title = {Estimating population immunity against serotype-two poliomyelitis from the inactivated polio vaccine in routine immunization across 112 countries: a modelling study},
year = {2026}
}

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TY  - JOUR
AB  - Background: To mitigate the risk of outbreaks of serotype 2 poliomyelitis after withdrawal of this sero- type from oral poliovirus vaccine (OPV) in 2016, inactivated poliovirus vaccine (IPV) was introduced into the routine immunization (RI) programmes of all countries using OPV. Since 2022, WHO has recommended a 2-dose schedule, with a first dose at 14 weeks of age followed by a second dose at least 4 months later (e.g. 14-39 week schedule), although an earlier schedule may be adopted, despite lower immunogenicity, if vaccine coverage is low at older ages. Methods and Findings: We combined published data on type-2 IPV seroconversion with age, national RI coverage estimates, dose introduction dates, and country-specific schedules using a cohort model of population immunity to estimate IPV-induced immunity from 2024-2031 for 112 countries using either one or two doses of IPV. We projected immunity for current, 6-14, and 14-39 week schedules to find the optimal schedule and estimate the impact of interventions such as schedule changes and catch-ups. Under current schedules, estimated median serotype 2 population immunity in 2025 among children under five years of age is at 61% (IQR: 52%, 72%), rising to 71% (IQR: 57%, 80%) in 2031. The later 14-39 week schedule was optimal in all countries, with potential for the median immunity to rise to 78% (IQR: 66%, 85%) by 2031 if adopted by all countries in 2026. Eight countries would still have < 50% immunity, rising to 65%-72% if catch-up campaigns with 80% coverage were implemented in 2030. The work is limited by the fact that IPV provides only a partial picture of total immunity where there has been emergency type-two OPV use. Furthermore, national estimates may mask subnational coverage differences and pockets of extremely low immunity.  Conclusions: Under these estimates, IPV schedules and coverage are suboptimal in many countries. Those with a single dose should introduce a second on the 14-39 week schedule; those on e
AU  - Gray,E
AU  - Cooper,L
AU  - Ramirez,Gonzalez A
AU  - Mach,O
AU  - Derqui,N
AU  - Grassly,N
AU  - Blake,I
PY  - 2026///
SN  - 1549-1277
TI  - Estimating population immunity against serotype-two poliomyelitis from the inactivated polio vaccine in routine immunization across 112 countries: a modelling study
T2  - PLoS Medicine
ER  - 

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