Ado Ibrahim carries his son Aminu through a village in northern Nigeria. Aminu was paralyzed by polio in August. Photo: David Gilkey / NPR
Northern Nigeria is the only region in the world where the number of polio cases is on the rise. International groups have poured money and volunteers into the area to combat the disease. But vaccinators face daunting challenges — from security threats like terrorist bombings to a lack of basic resources like electricity.