The worker was fatally injured and died while en route to the hospital. The gunmen’s identities were not revealed, but the Taliban previously issued threats against the Pakistan polio drive, BBC reports.
Officials suspended the vaccination program in several parts of Quetta after the shooting.
“We are investigating if the dead man had any dispute with the attackers or the shooting was carried out by opponents of the campaign,” Tariq Mengal, a senior local official, said, according to AFP.
Opposition to immunization drives is common in several parts of Pakistan, especially after a fake CIA vaccination plan helped locate Osama Bin Laden in 2011.
Militants kidnapped and killed foreign non-government organization workers in the past and a doctor administering polio vaccines in the southern city of Karachi was shot dead in July in an effort to stop the immunization drives. The militants claim that the drives are attempts by the workers to spy on them.
Pakistan, along with Nigeria and Afghanistan, is one of the three remaining countries where polio is still an endemic disease, BBC reports.