Estimating Population Immunity to Serotype 2 Poliomyelitis from IPV in Routine Immunization Acro

19 Mar 20264 min read0 viewsJournal Feed

GIST

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.

Clinical Editorial

Context and study aim

An earlier schedule may be used if RI coverage at older ages is low, though with lower immunogenicity.

The work examines how inactivated poliovirus vaccine (IPV)–induced immunity against serotype 2 poliomyelitis would accumulate under routine immunization (RI) programs after the 2016 withdrawal of serotype 2 OPV.
Since 2022, the World Health Organization has endorsed a two-dose IPV schedule (first at ~14 weeks, second at least four months later, e.g., 14–39 weeks).

Design and data synthesis

The researchers integrated published type-2 IPV seroconversion data with country-specific inputs, including RI coverage, the timing of dose introductions, and RI schedules, to build a cohort model of population immunity.
The model projects IPV-induced serotype-2 immunity from 2024 through 2031 for 112 countries and compares scenarios with one versus two IPV doses.
Scenarios evaluated include current schedules, a 6–14 week schedule, and a 14–39 week schedule, with attention to potential benefits from schedule changes and catch-up campaigns.

Key findings and signaling

Under current schedules, median estimated serotype-2 population immunity among children under five in 2025 is 61% (interquartile range [IQR] 52%–72%), rising to 71% (IQR 57%–80%) by 2031.
The later 14–39 week schedule consistently emerged as the optimal approach across all countries in the analysis.
If the 14–39 week schedule were adopted by all countries in 2026, median immunity could reach about 78% (IQR 66%–85%) by 2031.
Eight countries still fail to reach desired thresholds under the modeled conditions, indicating persistent gaps in immunity with current practices.

Context and interpretation

The analysis suggests IPV schedules and coverage are suboptimal in many settings.
For countries relying on a single IPV dose, introducing a second dose on the 14–39 week timetable is recommended.
Nations with earlier, suboptimal schedules would benefit from adopting the 14–39 week schedule.
Catch-up IPV campaigns are advised where RI coverage is insufficient to boost population-level immunity.

Limitations and uncertainties

The conclusions reflect model-based projections contingent on available seroconversion data and country-specific inputs; the source notes limitations inherent to modeling assumptions.