Vaccine-derived poliovirus (VDPV): Impact on poliomyelitis eradication.

The live attenuated strains used in the oral poliovirus (OPV) have been the main tool in the WHO polio eradication programme. However, these strains replicate in the human gut and are excreted for several weeks after immunisation. During this period, the attenuating mutations in the vaccine strains can rapidly revert. This may, in rare cases, cause vaccine-associated paralytic poliomyelitis (VAPP) in vaccinees or result in transmissible and neurovirulent circulating vaccine-derived poliovirus (cVDPV) strains. Outbreaks of poliomyelitis caused by VDPV have recently occurred in communities with long-term incomplete immunisation coverage. Hypogammaglobulinaemic vaccinees can chronically excrete immunodeficient VDPV (iVDPV) for several decades. As long as OPV is used, cVDPV and iVDPV pose a risk of causing poliomyelitis in unprotected individuals and threaten the goal of poliovirus eradication. VDPV cannot arise from the inactivated poliovirus vaccine (IPV), but financial and logistical barriers to replace OPV with IPV remain.