Two children in Nigeria have contracted polio, World Health Organizations officials confirmed Thursday. The outbreak of wild polio marks Africa's first cases in two years as the continent works to crack down on the almost-eradicated disease. August 11, the same day the new outbreak was announced, was meant to mark two years since Africa's last polio case. If Africa had gone three years without a new case of polio, the World Health Organization would have declared the continent polio-free.
