FILE - in this file photo taken Monday, Nov. 25, 2013, Pakistani health worker, Nooman Mehboob, 21, center, gives Ameeq Andriaz, 4, a polio vaccine, while other women holding their children wait to have them vaccinated in a neighborhood in Islamabad, Pakistan. The World Health Organization said the northwestern Pakistani city of Peshawar has become the largest poliovirus reservoir in the world. (AP Photo/Muhammed Muheisen, File)