The deadliest of Wednesday's attacks occurred in the northwestern town of Charsadda, where the female polio worker and her driver were gunned down, said senior government official Syed Zafar Ali Shah. Gunmen attacked two other polio immunization teams in Charsadda and one in the town of Nowshera, but no one was hurt in those attacks, he said.
Earlier in the day, gunmen shot a polio worker in the head in the city of Peshawar, wounding him critically, said Janbaz Afridi, a senior health official in surrounding Khyber Pakhtunkhwa province.
On Tuesday, gunmen killed five female polio workers — three of them teenagers — in a series of attacks in Karachi, the capital of southern Sindh province, and a village outside Peshawar. Two men who were working alongside the women were critically wounded in those attacks. A male polio worker was also shot to death in Karachi on Monday.
Police conducted two operations in Karachi in the wake of the shootings in which they arrested a dozen suspects and killed two suspected militants, said senior police official Shahid Hayat.
Several dozen polio immunization workers and human rights activists protested against the killings in Pakistan's capital, Islamabad, on Wednesday and demanded security for the field staff.
The Pakistani government also condemned the attacks, saying they deprive Pakistan's most vulnerable populations — specifically children — of basic life-saving health interventions. The U.N. said it was increasing security for its polio workers, but did not provide any details.
Polio usually infects children living in unsanitary conditions, attacks the nerves and can kill or paralyze. A total of 56 polio cases have been reported in Pakistan during 2012, down from 190 the previous year, according to the U.N. Most of the new cases in Pakistan are in the northwest, where the presence of militants makes it difficult to reach children.
The new campaign aimed to give oral polio prevention drops to 34 million children under the age of five. Clerics and tribal elders were recruited to support polio vaccinations in an attempt to open up areas previously inaccessible to health workers.
Associated Press writer Rasool Dawar in Peshawar, Pakistan, and Adil Jawad in Karachi, Pakistan, contributed to this report.