Three… Two… One?

On 10 November 2012, an 11 month old boy from Yobe in northern Nigeria became the last child to be paralyzed by wild polio virus type 3 (WPV3). More than two years on, no other case of the virus has been reported since, anywhere in the world. Experts are becoming quietly more confident that this means global WPV3 transmission may have been interrupted.

This would be a historic milestone for the Global Polio Eradication Initiative (GPEI), following on from the global eradication of wild poliovirus type 2 (WPV2) in 1999. It would mean that only one wild serotype – wild poliovirus type 1 (WPV1) – is still circulating anywhere in the world.

Two years with no cases of the virus is no guarantee of its eradication, however. One of the key dangers with WPV3 is that it is less virulent than WPV1, causing cases at a rate of approximately 1 in 1,000 infections (compared with 1 in 200 infections with WPV1). While causing fewer cases is a good thing, it also means the virus can transmit silently for longer without being detected. Continued surveillance is necessary before the global eradication of WPV3 can be conclusively determined, with more time being the strongest guarantee that the virus is not circulating without showing itself through cases of paralysis.

Despite this, the fact that no WPV3 has been detected for more than two years is extremely encouraging news for the global effort to eradicate all strains of this disease. It is a reminder that the eradication of polio is achievable, and that children everywhere will one day be free from the threat of this disease.

For more, please visit CDC’s Morbidity and Mortality Weekly Report article, ‘Possible Eradication of Wild Poliovirus Type 3’, from 14 November 2014.