Two gunmen riding a motorcycle fired at the vaccinators at Badabher area on the outskirts of Peshawar while they were administering polio drops to children.
One female vaccinator was killed instantly, police and witnesses said. The injured vaccinator was taken to Lady Reading Hospital, where doctors described her condition as critical.
Security forces cordoned off the area and launched a search operation for the gunmen. No group claimed responsibility for the attack though the Pakistani Taliban banned polio vaccinations in parts of the tribal belt last year, claiming the drive was a cover for espionage.
Following the attack, WHO announced it was temporarily suspending its vaccination campaign in Peshawar, the capital of Khyber-Pakhtunkhwa province.
A fresh three-day anti-polio campaign had been launched Tuesday in parts of Peshawar. President Asif Ali Zardari strongly condemned the attack on the female vaccinators, saying "such cowardly acts of militants and extremists cannot deter the strong resolve of the government to eradicate polio".
The government will not permit militants to deprive children of basic healthcare, he said. Zardari directed authorities to provide foolproof security to anti-polio vaccination teams so that they could continue their campaign.
On May 20, suspected militants attacked a team of polio vaccinators in the restive Bajaur tribal region and killed a security personnel.
Last month, a policeman was killed and another injured when suspected militants attacked a team of polio vaccinators in Mardan town of Khyber-Pakhtunkhwa.
In January, six women and a man working for a NGO involved in the vaccination campaign were shot dead in Swabi district. In December, eight volunteers involved in a polio vaccination drive were gunned down in a string of attacks in the southern port city of Karachi and Khyber-Pakhtunkhwa.
Pakistan, Afghanistan and Nigeria are the only countries where polio is still endemic.