Emergence of vaccine-derived poliovirus strains from the novel oral polio vaccine in the Central African Republic

The novel oral polio vaccine of serotype 2 (nOPV2) was engineered to prevent the emergence of revertant polio vaccine strains, which caused numerous outbreaks in the 2000s and 2010. Since 2021, it has been used in many countries, especially in Sub-Saharan Africa, to contain poliomyelitis outbreaks. In 2023, double recombinant nOPV2-derived isolates that had lost all the attenuation determinants were detected in the Central African Republic (CAR). Several of these were the first nOPV2 revertant isolates ever reported to the Global Polio Eradication Initiative, thereby demonstrating that the engineered modifications in nOPV2 do not entirely prevent reversion via recombination with non-polio enteroviruses of species Enterovirus coxsackiepol (EV-Cs). This study corroborates the increased genetic stability of nOPV2 compared to the historical vaccine strain but demonstrates that reversion through recombination with non-polio EV-Cs remains possible. This underscores the need for comprehensive EV-C surveillance alongside poliovirus monitoring, especially in Sub-Saharan Africa where EV-Cs are particularly abundant. In particular, assessing EV-C potential seasonal circulation patterns could inform the design of vaccination strategies tailored to minimize the risk of recombination between nOPV2 and non-polio EV-Cs.