A Pakistani health worker gives a polio vaccine to a child in slums of Lahore, Pakistan, Thursday, Jan. 23, 2014. Militants make heath workers targets of a number of their attacks, and gunmen killed three health workers yesterday in Karachi. The militants oppose vaccination against polio and consider such campaigns to be a cover for spying and claim the vaccine is intended to make Muslim boys sterile. According to the World Health Organization (WHO), Pakistan is the only polio-endemic country in the world, and it reported the most cases of the crippling disease in 2013 and 2012. Pakistan had 83 polio cases in 2013 and 58 cases in 2012.