Islamabad, June 9 : Gunmen shot dead two policemen guarding a team of polio vaccine workers in north-western Pakistan on Wednesday, police said, in the latest apparent attack on the campaign to eradicate the disease. The attack occurred in Mardan district of the conservative and volatile province of Khyber-Pakhtunkhwa, dpa reported. The health workers escaped the attack unhurt, police official Jumma Gul told dpa. Pakistan is two days into a five-day vaccination drive as part of a UN-funded campaign aimed at eradicating polio, which is still prevalent in Pakistan and Afghanistan. The campaign is targeting more than 30 million children under the age of 5. "We are in contact with local administration and assessing the situation for continuation of the campaign," a Health Ministry official said. The health workers, mostly young women, and police guards go door-to-door across the country to vaccinate children up to the age of five, multiple times a year. Militants linked with al-Qaeda often attack health workers. Dozens of vaccine handlers and security officials have been killed by Taliban militants in the past. The militants accuse the health workers of acting as spies and claim the polio vaccine is intended to make Muslim children sterile. Pakistan started a polio programme in 1994 and came very close to eliminating polio but recorded 147 cases, a five-year high, in 2019, amid vaccine boycotts and attacks on health workers. According to official statistics, only one case of polio has been reported so far this year. /IANS