Nine polio health workers have been killed in two attacks in northern Nigeria on Friday, following a spate of recent attacks on polio workers in Pakistan.

The Associated Press reports that the attacks took place in two neighborhoods of the largest city in Nigeria's north, Kano, when gunmen opened fire on the vaccinators.

Media reports indicate that Islamist group Boko Haram has been blamed for the killings.

A series of attacks have killed polio workers in Pakistan in recent weeks, possibly fueled by blowback from the fake vaccination drive used there to find bin Laden. The New York Times reported:

Some militants [in Pakistan] accuse polio workers of using vaccination campaigns as a cover to spy on behalf of the United States — a claim that has been fueled by the revelation that the C.I.A. used a vaccination drive as cover for the effort to find Osama bin Laden in Abbottabad in early 2011.

According to the World Health Organization, Nigeria and Pakistan are two of the three countries where polio remains endemic. Afghanistan is the third.