Suspected militants riding a motorcycle fired indiscriminately at a team of two female health workers at Kala area of Swabi district in Khyber-Pakhtunkhwa province.
Elite Force constable Munsif Khan, who was protecting the team, was killed instantly, police officials said.
The two vaccinators, who were administering the polio vaccine to some children inside a house, escaped unhurt.
Additional police forces cordoned off the area and launched a search operation.
No group claimed responsibility for the attack though the Taliban have for long opposed the polio vaccination campaign.
On January 1, six women and a man working for a NGO involved in polio vaccinations were shot dead in Swabi district.
Last month, eight volunteers involved in a polio vaccination campaign were gunned down in a string of attacks in the southern port city of Karachi and Khyber-Pakhtunkhwa province.
The attacks prompted UN agencies to withdraw their workers from the vaccination campaign.
