Wasn’t polio wiped out? Why it is still a problem in some countries

LONDON — Polio was eliminated from most parts of the world as part of a decadeslong effort by the World Health Organization and partners to wipe out the disease. Stopping polio outbreaks means vaccinating at least 95% of the population everywhere, including in conflict-ridden countries and poor regions with broken health systems and other priorities. But it contains weakened, live polio virus and in very rare cases can spread and cause polio in unvaccinated people. Health authorities have become more successful in reducing the number of cases caused by the wild polio virus. “The problem with trying to eradicate polio is that the need for perfection is so great and there are so many weak links,” said Scott Barrett, a Columbia University professor who has studied polio eradication.