In 2015, wild poliovirus transmission is at the lowest levels ever, with fewer cases reported from fewer areas of fewer countries than ever before. In 2015, 56 wild poliovirus cases have been reported from two countries (Pakistan and Afghanistan), compared to 290 cases from nine countries during the same period in 2014.
However, in the end stages of polio eradication, with most of the world polio-free, the risks posed remaining vaccination coverage gaps anywhere is becoming more evident. On extremely rare occasions, in areas of chronic vaccination coverage gaps, circulating vaccine-derived polioviruses (cVDPVs) can emerge to cause outbreaks of polio cases. This is not a side effect of the oral polio vaccine, but rather an effect of low vaccination coverage in a community, which is enabling such strains to emerge. Though typically less virulent than wild polioviruses (ie typically causing fewer cases and having a lower profile for geographic spread), such strains nevertheless are this year causing paralysis in children at a rate greater than wild polioviruses. More countries are affected by cVDPV outbreaks (Ukraine, Guinea, Lao, Nigeria, Madagascar) than wild polioviruses (Pakistan and Afghanistan); 3 WHO Regions are affected by cVDPV outbreaks.
Efforts are ongoing by the Global Polio Eradication Initiative to urgently address both remaining wild poliovirus transmission and cVDPV outbreaks. This is particularly important in the lead-up to next year’s start of the phased removal of OPVs, beginning with the globally-coordinated switch from trivalent OPV to bivalent OPV in April 2016.