The personnel were part of a nationwide anti-polio drive launched this week, aiming to inoculate tens of millions of children in Pakistan - one of only two countries where the crippling disease remains endemic.
Two gunmen on a motorcycle carried out the attack in the Lal Qila area of K-P province, near the border with Afghanistan, as police were gathering at a health centre before heading out with polio vaccinators, said police official Arif Shahbaz.
"The vaccinators were unhurt," added Shahbaz. Another police officer confirmed the incident and the toll.
The attack comes during a devastating year in Pakistan's long fight against the disease, with at least 104 cases reported in 2019 so far.
Year’s last polio campaign gets underway in K-P
Last year, just 12 cases were reported.
There was no immediate claim of responsibility for Wednesday's killings.
Vaccination campaigns have faced stubborn resistance for years in Pakistan, with many refusing to have their children inoculated because of misinformation and conspiracy theories.
But as Pakistan tries to reach its goal of eliminating polio from its territory, a new challenge has emerged in the form of a growing global movement against vaccinations.
The phenomenon has attracted adherents worldwide, fuelled by medically baseless claims and proliferated by social media resulting in a resurgence of once-eradicated, highly-contagious diseases.
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