Detection of vaccine-derived poliovirus type-3 in sewage of Kathmandu Valley, Nepal

Enteroviruses include polioviruses, which are classified into three types: type 1, type 2, and type 3. The oral polio vaccine (OPV), which contains attenuated strains of these three types, has been pivotal in reducing polio incidence worldwide. However, OPV can lead to vaccine-derived poliovirus (VDPV) cases, including circulating VDPV1 (cVDPV1), cVDPV2, and cVDPV3. In contrast, the inactivated or ‘killed’ polio vaccine (IPV), effectively prevents poliomyelitis without the risk of causing cVDPV cases. On 26 May 2024, a novel mutated form of poliovirus was detected in sewage samples from Kathmandu, Nepal, indicating an ongoing risk of poliovirus reintroduction and transmission. This finding highlights the importance of robust surveillance and containment measures. Historically, the Salk vaccine (IPV) and the Sabin vaccine (OPV) have been used against poliovirus, each with its advantages and limitations. Moving forward, it is necessary to replace OPV with genetically modified OPV, or new IPV formulations. Enhanced vaccination strategies and continued surveillance are crucial for achieving complete poliovirus eradication and preventing future outbreaks.