Key result
Simulated vaccination responses were predicted to substantially reduce cVDPV2 transmission and case burden, with the ability to stop the outbreak by February 2021.
Why the study?
Pakistan and Afghanistan faced an outbreak of cVDPV2 alongside WPV1 and SARS-CoV-2, making it critical to understand transmission risks from paused global vaccination and evaluate response strategies during COVID-19 mitigation.
Outbreak response vaccination campaigns against cVDPV2 must be implemented urgently when feasible to stop transmission despite COVID-19 pandemic challenges.
Answers are grounded in this paper and cite their sources.
Vaccination responses can interrupt cVDPV2 despite COVID disruptions; modeling leaves open optimal strategies amid WPV1 co-circulation.
BACKGROUND: Since July 2019, Pakistan and Afghanistan have been facing an outbreak of serotype-2 circulating vaccine derived poliovirus (cVDPV2) in addition to continued transmission of serotype-1 wild poliovirus (WPV1) and SARS-CoV-2 in 2020. Understanding the risks of cVDPV2 transmission due to pause of global vaccination efforts and the impact of potential vaccination response strategies in the current context of COVID-19 mitigation measures is critical. METHODS: We developed a stochastic, geographically structured mathematical model of cVDPV2 transmission which captures both mucosal and humoral immunity separately and allows for reversion of serotype-2 oral polio vaccine (OPV2) virus to cVDPV2 following vaccine administration. The model includes geographic heterogeneities in vaccination coverage, population immunity and population movement. The model was fitted to historic cVDPV2 cases in Pakistan and Afghanistan between January 2010-April 2016 and July 2019-March 2020 using iterated particle filtering. The model was used to simulate spread of cVDPV2 infection from July 2019 to explore impact of various proposed vaccination responses on stopping transmission and risk of spread of reverted Sabin-2 under varying assumptions of impacts from COVID-19 lockdown measures on movement patterns as well as declines in vaccination coverage. RESULTS: Simulated monthly incidence of cVDPV2 from the best-fit model demonstrated general spatio-temporal alignment with observed cVDPV2 cases. The model predicted substantial spread of cVDPV2 infection, with widespread transmission through 2020 in the absence of any vaccination activities. Vaccination responses were predicted to substantially reduce transmission and case burden, with a greater impact from earlier responses and those with larger geographic scope. While the greatest risk of seeding reverted Sabin-2 was predicted in areas targeted with OPV2, subsequent spread was greatest in areas with no or delayed response. The proposed vaccination strategy demonstrated ability to stop the cVDPV2 outbreak (with low risk of reverted Sabin-2 spread) by February 2021. CONCLUSION: Outbreak response vaccination campaigns against cVDPV2 will be challenging throughout the COVID-19 pandemic but must be implemented urgently when feasible to stop transmission of cVDPV2.
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Molodecky et al. (2021) studied serotype-2 circulating vaccine derived poliovirus (cVDPV2) outbreak. Outbreak response vaccination campaigns (OPV2) vs. No vaccination activities was evaluated on Spread of cVDPV2 infection and risk of reverted Sabin-2 spread. Simulated vaccination responses were predicted to substantially reduce cVDPV2 transmission and case burden, with the ability to stop the outbreak by February 2021.
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