Stopping Vaccine-Derived Poliovirus Outbreaks

Any polio outbreak begins in the same way: a child complaining of a headache and a fever. Within just a few hours, the virus causes rapid onset, floppy, paralysis, for which there is no cure. Whether caused by one of the three strains of wild poliovirus (WPV) or by circulating vaccine derived poliovirus (cVDPV), the result of is the same: a lifetime of paralysis that could have been prevented with a simple vaccine.

The Global Polio Eradication Initiative (GPEI) works to stop all types of the virus permanently, to provide a polio-free world for future generations. In 2014 and 2015, cases of paralysis caused by cVDPVs have been reported in Madagascar, Mali, Nigeria, Pakistan, South Sudan and Ukraine. The GPEI responds to children paralysed by cVDPVs just as they would to an outbreak of WPV- with technical support to the country, strengthened and expanded surveillance, community engagement and a rapid, large scale immunization response.

Preventing outbreaks of cVDPV

A cVDPV is an extremely rare strain of polio genetically changed from its original, weakened strain contained in oral polio vaccine (OPV).  Excreted vaccine-viruses can find susceptible children and begin to circulate beyond the immediate household into the broader community, which in the vast majority of cases is a positive thing, spreading the protection of the vaccine further. However, the longer it is allowed to survive this way in areas where not all children are receiving the vaccines, the more genetic changes it undergoes as it replicates, and eventually it can revert to the point that it can cause paralysis. Circulating VDPVs are viruses that have gone through this process. Therefore cVDPVs are the consequence of failure to vaccinate children, rather than of the vaccine itself.

Circulating VDPV events are extremely rare. Over the past 10 years, more than 10 billion doses of OPV have been administered to more than 2.5 billion children, preventing more than 650,000 polio cases every single year. In that same period, only 21 cVDPV episodes are known to have occurred, resulting in 622 cases. But a child paralysed by any polio virus is irrevocably affected for life, and so once wild polioviruses have been successfully eradicated, OPV must be phased out, as the public health benefits of OPV will no longer outweigh the very small risk of its continued use.

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Written By Beyond Polio