Unidentified militants opened fire on a polio vaccination team in Pakistan on Tuesday, killing one of those handing out doses and two policemen, officials said.

A child was injured in the attack and there was no immediate claim of responsibility. The attack in the northwest region bordering Afghanistan comes a day after Pakistan launched its latest national campaign to stamp out the virus, which still poses a health threat in the South Asian nation, although mostly eradicated elsewhere.

“Unknown militants opened fire at a polio team,” according to an official report from the region’s deputy commissioner that listed the casualties and added that a search for the culprits had begun.

Pakistan reported three new polio cases this year after a gap of 15 months, all in the northwest province of Khyber Pakhtunkhwa which borders Afghanistan.

Pakistan and Afghanistan are the only two countries in the world still struggling to eradicate polio.