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. 2024 Feb;44(2):379-389.
doi: 10.1111/risa.14159. Epub 2023 Jun 21.

Worst-case scenarios: Modeling uncontrolled type 2 polio transmission

Dominika A Kalkowska  1 , Eric Wiesen  2 , Steven G F Wassilak  2 , Cara C Burns  3 , Mark A Pallansch  4 , Kamran Badizadegan  1 , Kimberly M Thompson  1
Affiliations

Worst-case scenarios: Modeling uncontrolled type 2 polio transmission

Dominika A Kalkowska et al. Risk Anal. 2024 Feb.

Abstract

In May 2016, the Global Polio Eradication Initiative (GPEI) coordinated the cessation of all use of type 2 oral poliovirus vaccine (OPV2), except for emergency outbreak response. Since then, paralytic polio cases caused by type 2 vaccine-derived polioviruses now exceed 3,000 cases reported by 39 countries. In 2022 (as of April 25, 2023), 20 countries reported detection of cases and nine other countries reported environmental surveillance detection, but no reported cases. Recent development of a genetically modified novel type 2 OPV (nOPV2) may help curb the generation of neurovirulent vaccine-derived strains; its use since 2021 under Emergency Use Listing is limited to outbreak response activities. Prior modeling studies showed that the expected trajectory for global type 2 viruses does not appear headed toward eradication, even with the best possible properties of nOPV2 assuming current outbreak response performance. Continued persistence of type 2 poliovirus transmission exposes the world to the risks of potentially high-consequence events such as the importation of virus into high-transmission areas of India or Bangladesh. Building on prior polio endgame modeling and assuming current national and GPEI outbreak response performance, we show no probability of successfully eradicating type 2 polioviruses in the near term regardless of vaccine choice. We also demonstrate the possible worst-case scenarios could result in rapid expansion of paralytic cases and preclude the goal of permanently ending all cases of poliomyelitis in the foreseeable future. Avoiding such catastrophic scenarios will depend on the development of strategies that raise population immunity to type 2 polioviruses.

Keywords: dynamic modeling; eradication; interdependent risks; oral poliovirus vaccine; polio.

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Figures

Figure 1.
Figure 1.
Variability among 100 stochastic iterations for RC with outbreak response using mOPV2, best nOPV2, or worst nOPV2 for (a) 2022–2026 and (b) 2022–2035
Figure 1.
Figure 1.
Variability among 100 stochastic iterations for RC with outbreak response using mOPV2, best nOPV2, or worst nOPV2 for (a) 2022–2026 and (b) 2022–2035
Figure 2.
Figure 2.
10 (out of 100) worst performing stochastic iterations for RC with outbreak response for the 2022–2026 time horizon using (a) mOPV2, (b) best nOPV2, or (c) worst nOPV2
Figure 3.
Figure 3.
10 (out of 100) worst performing stochastic iterations for RC with outbreak response for 2022–2035 time horizon using (a) mOPV2, (b) best nOPV2, or (c) worst nOPV2
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