Nobody will ever know the identity of the thousands of African children who were not killed or paralyzed by polio this year. They would have been hard to keep track of no matter what because in ordinary times, they would have followed thousands last year and thousands the year before and on back in a generations-long trail of suffering and death.

Instead, no African children were claimed by polio this year or last year or the year before. It was in 2016 that the last case of wild, circulating polio was reported in Nigeria—the final country on the 54-nation African continent where the disease was endemic. And with a required multi-year waiting period now having passed with no more cases, the World Health Organization today officially declared the entirety of Africa polio-free. A disease that as recently as the late 1980s was endemic in 125 countries, claiming 350,000 children per year, has now been run to ground in just two remaining places, Pakistan and Afghanistan, where there have been a collective 102 cases so far in 2020. That’s 102 too many, but there is no denying the scope of the WHO announcement.