A Pakistani girl shows finger marked after being immunized in Lahore, Pakistan on Wednesday, Dec. 19, 2012. Gunmen shot dead a woman working on U.N.-backed polio vaccination efforts and her driver in northwestern Pakistan on Wednesday, officials said, raising the number of people killed in the last 48 hours who were part of the immunization drive. (AP Photo/K.M. Chaudary)

Associated Press
A Pakistani girl shows finger marked after being immunized in Lahore, Pakistan on  Wednesday, Dec. 19, 2012. Gunmen shot dead a woman working on U.N.-backed polio vaccination efforts and her driver in northwestern Pakistan on Wednesday, officials said, raising the number of people killed in the last 48 hours who were part of the immunization drive. (AP Photo/K.M. Chaudary)
A Pakistani girl shows finger marked after being immunized in Lahore, Pakistan on Wednesday, Dec. 19, 2012. Gunmen shot dead a woman working on U.N.-backed polio vaccination efforts and her driver in northwestern Pakistan on Wednesday, officials said, raising the number of people killed in the last 48 hours who were part of the immunization drive. (AP Photo/K.M. Chaudary)
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