A Nigerian schoolboy is vaccinated against polio during a mass nationwide polio inoculation April 12, 2005, in Kano, Nigeria.
Diego Ibarra Sánchez / TIME
A child is vaccinated against polio at Toll Plaza, on the outskirts of Karachi.
Saurabh Das / AP
A child is administered polio drops by a mobile unit during an anti-polio drive in New Delhi, India, Sunday, Jan. 15, 2012. India marked a full year since its last reported case of polio on Friday, Jan. 13.
JAGADEESH NV / REUTERS
A ten-year-old polio victim in Bangalore, India
NARINDER NANU / AFP / Getty Images
An Indian Sikh boy receives polio vaccination drops from a medical volunteer during an immunisation drive outside the Golden Temple in Amritsar on Feb. 24, 2013
Fayaz Aziz / Reuters
An Afghan refugee woman waits her turn to receive a drop of polio vaccine for her child at the United Nations High Commissioner for Refugees supported Jalozai camp on the outskirts of Peshawar, Sept. 25, 2012.
Bill Gates gives a baby an oral polio drop at a community health clinic in Andhra Pradesh
CHRIS HONDROS / GETTY
POLIO: After a year-long hiatus, children in Nigeria are once again getting oral vaccines
Ben Curtis / AP
In this Wednesday April 24, 2013 file photo a Somali baby receives a polio vaccine, at the Medina Maternal Child Health center in Mogadishu, Somalia.
Chris Hondros / Getty Images
Teams Give Polio Vaccine in Massive Nigerian Innoculation