A new study in BMJ Global Health aims to estimate outbreak risk and costs, given the importation of wild poliovirus serotype 1 (WPV1) for non-endemic countries in the WHO Africa region. Preventing importations and spread of wild poliovirus serotype 1 (WPV1) is critical and dependent on population immunity provided through routine immunization (RI) and supplementary immunization activities (SIAs).
Researchers developed a stochastic mathematical model of polio transmission dynamics to evaluate the probability of an outbreak, expected number of poliomyelitis cases, costs and incremental cost-effectiveness ratios under different vaccination strategies. Across variable RI coverage, three key strategies were explored:
Results are presented in 2023 USD over a 5 year- time horizon from the Global Polio Eradication Initiative (GPEI) and health system perspectives.
The annual pSIA strategy has the greatest probability of no outbreaks in comparison to other strategies: under our model assumptions, annual pSIAs result in an 80% probability of no outbreaks when RI coverage is ≥50%. The biennial pSIA strategy requires RI coverage ≥65% to achieve an equivalent risk of no outbreaks. The strategy with no pSIAs requires ≥75% RI coverage to achieve an equivalent risk of no outbreaks.
For the health system, when RI coverage is between 35% and 60%, both pSIA strategies are cost-saving. For the GPEI, below 65% RI pSIA strategies are cost-effective, but the biennial pSIA strategy incurs higher costs in comparison to annual pSIAs due to more oSIAs required to stop outbreaks. Prioritization of pSIAs must balance outbreak risk against implementation costs, ideally favoring the smallest manageable outbreak risk compatible with elimination. Authors infer that there are few short-term risks due to population immunity from RI, but without pSIAs, long-term risks accumulate and can result in outbreaks with the potential for international spread.
Thumbnail image credit: Gavi/2021/Christophe Da Silva
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