cVDPVs

Circulating vaccine-derived poliovirus (cVDPV) refers to poliovirus strains that originated from the attenuated Sabin strains used in oral polio vaccine (OPV) and have accumulated mutations during replication in under-immunized populations. When such vaccine-derived viruses continue to circulate in a community, they can regain neurovirulence and transmissibility, causing outbreaks of poliomyelitis that resemble those caused by wild poliovirus. The illness can range from asymptomatic infections to paralytic poliomyelitis, with paralysis occurring in a minority of cases.

cVDPVs are classified into serotypes 1, 2, and 3 (cVDPV1, cVDPV2, cVDPV3). They are distinguished from immunodeficiency-associated VDPVs (iVDPVs), which arise from prolonged shedding by people with immune system deficiencies and do not indicate sustained community transmission. A cVDPV isolate is typically defined by genetic divergence in the VP1 gene from the corresponding Sabin strain of more than about 1% and evidence of circulation for an extended period, though exact criteria can vary by surveillance system.

Epidemiologically, cVDPVs have caused outbreaks in regions with gaps in immunization and weak public health infrastructure, including parts of Africa, Asia, and the Middle East. Detection relies on acute flaccid paralysis surveillance and environmental surveillance, such as testing sewage for poliovirus. Outbreak responses combine vaccination campaigns using OPV (types 1 and 3 with bOPV, and type 2 with monovalent or novel vaccines) and inactivated polio vaccine to strengthen immunity and halt transmission. Novel oral vaccines with greater genetic stability are being pursued to reduce the risk of reversion and future cVDPV emergence.