Cameroonian soldiers stand guard at a lookout post on Feb. 25 as they take part in operations against the Islamist extremist group Boko Haram in northern Cameroon, near the border with Nigeria. Edwin Kindzeka Moki/AP hide caption

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No one knows how many children have been affected by the spread of Boko Haram across Nigeria and neighboring countries. This photo shows the school uniforms of the girls kidnapped from a school a year ago. Glenna Gordon/Glenna Gordon for NPR hide caption

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On the outskirts of Islamabad, a Pakistani health worker vaccinates an Afghan refugee against polio. Muhammed Muheisen/AP hide caption

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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

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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

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