“True polio eradiation is zero incidence of polio virus infection, by both wild and vaccine viruses. This new definition was universally accepted only last year,” said Dr. T. Jacob John, member of the WHO committee on global polio eradication.
The root cause of the problem is the use of live, weakened polio viruses in the oral polio vaccine (OPV) for inducing immunity against the wild-type virus. Although weakened, the viruses are still alive and can “quite often” undergo genetic changes (back-mutate) to cause neuro-virulence (polio). Hence the very vaccine that is supposed to protect children against polio causes the disease.
“There are only 15 per cent genetic differences between wild polio viruses and the weakened viruses used in oral polio vaccine,” said Dr. John. The weakened viruses in OPV are genetically highly unstable and have a tendency to drift back to the wild (back-mutate) and become neuro-virulent.