Vaccine-associated paralytic polio (VAPP) and vaccine-derived poliovirus (VDPV)

The oral polio vaccine (OPV) is an extremely safe and effective tool for immunizing children against polio. Over the past 10 years, more than 10 billion doses of OPV have been administered to over 2.5 billion children worldwide, preventing more than 10 million polio cases during that period. On very rare occasions, OPV can lead to vaccine-associated paralytic polio or vaccine-derived poliovirus. These are similar but different phenomena.