In this Wednesday, Jan. 30, 2013, photo, a Pakistani police officer, right, guards a group of health workers going from house to house to give polio vaccines to children, in Islamabad, Pakistan. ... more 
In this Wednesday, Jan. 30, 2013, photo, a Pakistani police officer, right, guards a group of health workers going from house to house to give polio vaccines to children, in Islamabad, Pakistan. Gunmen killed a policeman who was guarding a polio vaccination team on Monday, May 20, 2013, in Pakistan's northwest Bajur tribal area, said local government administrator Faramosh Khan. (AP Photo/Muhammed Muheisen) less 
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Associated Press | Photo By Muhammed Muheisen
Mon, May 20, 2013 1:08 PM EDT