Quantifying the Impact of Vaccinating Under-Immunized Groups in Polio Outbreaks: A Simulation-Based Study

Polio, an infectious disease that causes paralysis, remains a global health concern, especially with the emergence of circulating vaccine-derived poliovirus (cVDPV) and recurring outbreaks in areas with cohorts of under-immunized individuals. This study assessed how the allocation of vaccines during a polio outbreak response might impact outcomes. Adapting a compartmental simulation model, we projected poliovirus transmission from 2024 to 2026 under different levels of vaccination campaign coverage (i.e., the proportion of the target population reached by vaccination), vaccine allocation schemes (e.g., across different immunity groups), and vaccination campaign delays. Results highlighted that compared to other allocation schemes, priority allocation of vaccines to under-immunized groups (i) significantly reduced the number of paralytic cases, even with lower coverage and longer delay; (ii) achieved die-out of transmission with two rounds of vaccination if the delay was short (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\le$</tex> 3 weeks) and coverage was high (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\ge$</tex> 70%).