Gunmen fatally shot a police officer assigned to protect polio workers in Pakistan’s northwest, an official said Tuesday. At least 10 police have died this year while on security duty for vaccination campaigns in Khyber Pakhtunkhwa province. The gunmen fired at a team working in Bajaur district, killing the officer on the spot, police officer Dilawar Khan said. No one immediately claimed responsibility for the assault. Anti-polio campaigns in Pakistan are regularly marred by violence. Militants target vaccination teams and police assigned to protect them, falsely claiming that the campaigns are a Western conspiracy to sterilize children. A five-day anti-polio campaign started Monday in 13 high-risk districts of Khyber Pakhtunkhwa. More than 21,000 teams are tasked with administering vaccines to 4,423,000 children under age 5. More than 32,000 police are protecting the teams. Pakistan and neighboring Afghanistan are the only countries where the spread of polio has never been stopped. The potentially fatal, paralyzing disease mostly strikes children under age 5 and typically spreads through contaminated water.