A Pakistani police spokesman says gunmen have killed three women working on a polio vaccination campaign, along with their driver.
The women's driver was also killed in the attack on November 26 on the outskirts of Quetta, a western city near the Afghan border.
Police spokesman Shahzada Farhat said the women and their driver were waiting for a police escort to arrive when two men on a motorcycle pulled beside them and opened fire.
Militants have frequently targeted people involved in dispensing polio vaccinations, claiming the immunization program is a cover for spying.
The attacks have contributed to an increase in polio cases in Pakistan, which now stand at a 15-year high, making Pakistan one of only three countries in the world where polio remains endemic.
The World Health Organization has registered 235 polio cases in Pakistan this year.