Public health experts hope a new vaccine, introduced in seven countries this year, will significantly reduce the incidence of polio cases in communities where children are not immunized and exposed to poor sanitation. But limited production is currently curtailing its reach.
There are, essentially, two different categories of viruses that can cause polio. One is “wild” polio — the form of the virus believed to be in circulation for thousands of years. Its elimination is on the horizon, with cases now only found in Afghanistan and Pakistan.
But the goal of eliminating polio in its entirety is complicated by a rise in cases of the “circulating vaccine-derived polioviruses,” or cVDPV. After a child is immunized through the oral poliovirus vaccine, remnants of the weakened poliovirus can leave the child’s body through feces, which can then enter the surrounding environment. Other children can then be exposed to the virus through contamination. And if population immunity is low and the virus is allowed to circulate, over time it can change into a form of the poliovirus that can cause paralysis.