Some 19 polio vaccination workers have now died in attacks in Pakistan in the last two months, Geo TV reported Thursday.
The men were killed by a roadside bomb as they visited a village in the upper Kurram tribal region, said Jawal Ali, the head of the campaign in that area.
No group claimed responsibility for the deaths, but the Taliban last year banned such vaccinations in Waziristan, terming the effort a cover for espionage.
A policeman guarding two female polio workers was shot to death Tuesday in the Swabi district where seven staff members of a charity involved in polio vaccinations were killed Jan. 1.
Nine health workers were killed in December in Karachi and the northwest.