What is vaccine-derived polio?
Q: What is vaccine-derived polio?
A: Oral polio vaccine (OPV) contains a weakened version of poliovirus, activating an immune response in the body. A vaccinated person transmits the weakened virus to others, who also develop antibodies to polio, ultimately stopping transmission of poliovirus in a community. In very rare instances, the virus in the vaccine can mutate into a form that can paralyse - this is what is known as a vaccine-derived poliovirus or VDPV. If this virus regains the ability to circulate, it is called a circulating vaccine-derived poliovirus (cVDPV). As with naturally occurring poliovirus, the only protection against cVDPV is full vaccination.
The spread of a cVDPV shows that too many children remain under-immunized. A fully-immunized population will be protected from all strains of poliovirus, whether wild or vaccine-derived.
Over the past 10 years, more than 10 billion doses of OPV have been administered to more than 2.5 billion children. As a result more than 3.5 million polio cases were prevented. During that time, 18 outbreaks of cVDPVs have occurred in 16 countries, resulting in 510 VDPV cases.
The small risk of VDPVs pales in significance to the tremendous public health benefits associated with OPV. Every year, hundreds of thousands of cases due to wild polio virus are prevented. Well over eight million cases have been averted since large–scale administration of OPV began 20 years ago.
Circulating VDPVs in the past have been rapidly stopped with 2–3 rounds of high-quality immunization campaigns. The solution is the same for all polio outbreaks: immunize every child several times with the oral vaccine to stop polio transmission, regardless of the origin of the virus.
