A soldier guards polio vaccination team administering polio vaccination to children during a three-day countrywide vaccination campaign in Peshawar, Pakistan. Though new polio cases dropped to a nine-year low in 2016, attacks by Islamist militants against health workers and police guarding them remained a challenge for a UN-funded vaccination campaign. Photo Arshad Arbab/EPA
An Afghan girl looks on as a health worker administers polio vaccine drops to others during a vaccination campaign on the outskirts of Jalalabad. Polio, once a worldwide scourge, is endemic in just three countries now – Afghanistan, Nigeria and Pakistan. Photo Noorullah Shirzada/AFP/Getty
Police guard a polio vaccination team, during a three-day vaccination campaign in Karachi. Pakistan. Though new polio cases dropped to a nine-year low in 2015, attacks by Islamist militants against health workers and police guarding them remained a challenge for a UN-funded vaccination campaign.
AP Photo/Allauddin Khan
An Afghan burqa clad female health worker gives a vaccination to a child during a polio campaign in Kandahar, Afghanistan, on Monday
A Pakistani health worker administers polio drops to a young girl during a polio vaccination campaign in Karachi on Monday
A health worker administers a polio vaccine to a child, in Peshawar, Pakistan on Monday. Pakistan still accounts for the majority of polio cases globally
A girl receives polio vaccination during an anti-polio campaign on the outskirts of Jalalabad on Monday
Girls show off their painted fingers after receiving the polio vaccine in Lahore, Pakistan, on Tuesday
Metin Aktas/Anadolu Agency/Getty Images
Pakistani health workers mark the thumb of a child after giving him vaccine during a polio vaccination campaign in Rawalpindi, Pakistan. Pakistani health workers go door to door to administer vaccinations to children for diseases including polio, tuberculosis, tetanus, whooping cough, measles and hepatitis.
A woman in Islamabad, Pakistan, takes her child to a health worker to be vaccinated against polio. More than a dozen polio vaccine workers have been killed by militants in the past year in the country. They claim the workers are spies and the vaccination is intended to make Muslim children sterile.