Senior police official Shafiullah Khan said two attackers on foot fired a pistol at the women. He said police have started a search operation.
Pakistan militants have increasingly attacked polio workers because they suggest the vaccine actually harms children and also that the health workers are spying for the United States, according to Radio Free Europe.
The attacks have made it harder for Pakistan to join the vast majority of nations declared polio-free, and late Tuesday, government officials were debating whether to suspend the U.N.-backed vaccination campaign in the northwest.
Vaccination workers in Nigeria and Aghanistan have also been killed in recent months, according to the Los Angeles Times.
In separate attacks last December in Pakistan, gunmen killed at least nine polio workers. Police officers assigned to protect the workers have also been killed or injured.
Meanwhile, the number of polio cases dropped from 173 in 2011 to 56 in 2012.
The Associated Press contributed to this report.