by Elizabeth J. Gray, Laura V.
Cooper, Alejandro Ramirez Gonzalez, Ondrej Mach, Nieves Derqui, Nicholas C. Grassly, Isobel M.
Blake Background To mitigate the risk of outbreaks of serotype 2 poliomyelitis after withdrawal of this serotype 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 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 early schedules would benefit from adopting the 14–39 week schedule.
IPV catch-up campaigns are recommended where RI coverage is low.
PLOS Medicine published a clinical update in Research Highlights on 19 Mar 2026. The item focuses on Estimating population immunity against serotype-two poliomyelitis from the inactivated polio vaccine in routine immunization across 112 countries: A modelling study. Open the detail page to review the full original feed content.