Islamabad (CNN) A string of deadly attacks in Pakistan targeting healthcare workers has sparked fears that the spread of misinformation is fueling a resurgence of violence against those attempting to rid the country of polio.

Attacks were reported on Monday in Bannu, Wednesday in Buner and Thursday in Quetta. One polio vaccination worker and two policemen have been killed.

Public health experts say there is concern that these attacks are exacerbating what is already one of the world's most intractable public health threats.

Pakistan is one of only three countries to have failed in its bid to stop the transmission of polio, according to the World Health Organization . That is in part due to a historical distrust of foreign healthcare providers, concerns that were inflamed after allegations surfaced that US intelligence officials had used a fake vaccination program in the Pakistani city of Abbottabad as part of efforts to capture Osama bin Laden in 2011.

Islamist militants have attacked and killed those attempting to distribute vaccines since the bin Laden revelation.

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