Gunmen murdered a woman in Peshawar, Pakistan, Wednesday who was working on a United Nations-backed polio vaccination campaign immunizing children. Her driver was also killed.
On Monday and Tuesday, one male World Health Organization volunteer and five female health workers administering vaccines in Karachi were also murdered.
Though no one has yet claimed responsibility, officials suspect the Taliban is behind the deadly attacks. The terrorist group has opposed efforts to fight polio in the region.
"It's a very grim situation," a government official in the provincial area where the attacks occurred told CBS News. "The Taliban are making certain that this (anti-polio) campaign fails completely."
Both campaigns were a part of a three-day push by the government to vaccinate the highest risk parts of the country.
The Pakistani government has now suspended vaccinations in two cities because of the attacks.