A child receives a polio vaccine Sunday in Kano, Nigeria. The country is the primary source of the virus in Africa but appears to be making progress against the disease; the current outbreak in Cameroon that has spread to Equatorial Guinea came by way of Chad, not Nigeria. Sunday Alamba/AP hide caption

itoggle caption Sunday Alamba/AP

Sylvestre Mebam (right) runs an unauthorized health clinic in Cameroon's largest city of Douala. He and his assistant treat about 10 to 15 people each day. Andres Caballero/NPR hide caption

itoggle caption Andres Caballero/NPR