Islamabad, Pakistan (CNN) -- Health workers administering polio vaccinations to children came under attack in northern Pakistan on Tuesday, killing their police escort, authorities said.
Two women administering the shots entered a house on the outskirts of Mardan when two assailants on a motorbike opened fire of them, according to Danishwar Khan, a local police official. The women were not injured.
Attacks like these have become a frequent occurrence in some parts of Pakistan and have left 10 workers dead.
Pakistan is one of three countries in the world where polio has yet to be eradicated.
Pakistanis have viewed polio vaccination campaigns with suspicion after the CIA's use of a fake vaccination program in 2011 to collect DNA samples from residents of Osama bin Laden's compound to verify the al Qaeda leader's presence there.
Bin Laden was killed by U.S. forces in May 2011.
In June, a Taliban commander in northwest Pakistan announced a ban on polio vaccines for children in the region as long as the United States continues its campaign of drone strikes in the region, the Taliban said.
It wasn't immediately clear if the Taliban played a role in Tuesday's attacks.
Polio, a highly infectious viral disease that can cause permanent paralysis in a matter of hours, has been eradicated around the world except for three countries where it is endemic: Pakistan, Nigeria and Afghanistan.
After the number of cases spiked sharply last year, Pakistan stepped up its eradication efforts. The numbers fell from 173 in 2011 to 58 in 2012, according to the Global Polio Eradication Initiative.