How can vaccine-derived poliovirus arise from oral polio vaccine?

Vaccine-derived polioviruses (VDPVs) arise from the oral poliovirus vaccine (OPV) because the vaccine contains live, attenuated (weakened) poliovirus.12

After a person receives the vaccine, the weakened virus replicates in their small intestine and is subsequently shed through their feces. In rare instances, particularly in populations with low immunization rates, the attenuated virus can undergo genetic mutations as it circulates. Through a process of reversion, the virus can mutate back into an infectious form capable of causing paralysis and attacking the nervous system.13

While these occurrences are rare, they represent a significant public health challenge, leading many high-income countries to transition to the inactivated poliovirus vaccine (IPV), which uses killed virus and carries no risk of VDPV. However, OPV remains a vital tool in global eradication efforts due to its effectiveness in improving herd immunity in areas with ongoing transmission.12