Key result
A 14-39 week IPV schedule could increase pediatric serotype 2 immunity to ~78% versus current schedules.
Why the study?
To estimate population immunity and determine optimal IPV schedules following the withdrawal of serotype 2 oral poliovirus vaccine and WHO recommendations for a 2-dose routine immunization schedule.
What is the optimal schedule for the inactivated poliovirus vaccine to maximize population immunity against serotype-two poliomyelitis in children under five?
What is the optimal schedule for the inactivated poliovirus vaccine to maximize population immunity against serotype-two poliomyelitis in children under five?
A 14-39 week schedule for the inactivated poliovirus vaccine is projected to optimize population immunity against serotype-two poliomyelitis compared to earlier schedules.
Answers are grounded in this paper and cite their sources.
May warrant adopting a 14-39 week IPV schedule routinely; extends models projecting superior median serotype 2 population immunity.
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 <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-2 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 early schedules would benefit from adopting the 14–39 week schedule. IPV catch-up campaigns are recommended where RI coverage is low.
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Gray et al. (2026) studied this question. A 14-39 week inactivated poliovirus vaccine schedule could increase median serotype 2 immunity among children under five to 78% by 2031, compared to 71% under current schedules.
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