Gunmen kill a polio worker during a vaccination campaign in Pakistan

Pakistani police say gunmen on motorcycles opened fire on police escorting a team of polio workers during a door-to-door vaccination campaign in the northwest, killing an officer and a polio worker. No one immediately claimed responsibility for Wednesday's attack in Bajur, a district in the Khyber Pakhtunkhwa province and a former stronghold of the Pakistani Taliban. Pakistan on Monday launched a nationwide anti-polio campaign amid a spike in militant attacks. The potentially fatal, paralyzing disease mostly strikes children under age 5 and typically spreads through contaminated water. Pakistan and Afghanistan are the only countries in which the spread of polio has never been stopped.