The vaccinators were attacked while they administering polio drops to children in Swabi area of Khyber-Pakhtunkhwa province, officials said.
This was the second such attack in Swabi.
In January, six women and a man working for a NGO involved in the vaccination campaign were shot dead in the district.
Last month, the killing of a female polio vaccinator on the outskirts of Peshawar city had prompted the World Health Organisation to suspend its vaccination campaign.
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On May 20, suspected militants attacked a team of polio vaccinators in the restive Bajaur tribal region and killed a security personnel.
In April, a policeman was killed and another injured when suspected militants attacked a team of polio vaccinators in Mardan town of Khyber-Pakhtunkhwa.
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.