In the southern port city of Karachi, two woman workers and a man were killed and two others injured when unidentified gunmen fired at them in Qayummabad area. The team was working without any security.
According to witnesses, four armed men were waiting in the area and attacked the team as soon as it entered the neighbourhood.
Unidentified armed men opened fire at a vaccination team at Mansehra in the country's restive northwest and killed one worker, The Express Tribune reported on its website.
The attacks came a day after health authorities in Sindh province, of which Karachi is the capital, launched a drive to inoculate 7.6 million children as part of a nationwide campaign against polio that will continue till Thursday.
Also Read
The first day of the drive concluded without any untoward incident.
Pakistan is one of only three countries where polio is still endemic, but efforts to stamp out the disease have been hit by repeated attacks on health teams. Pakistan registered more than 80 polio cases last year.
Most attacks on polio workers in Karachi have occurred in areas on the outskirts of the city that are considered Taliban strongholds.
Yesterday, Prime Minister Nawaz Sharif said Pakistan remains strongly committed to eradicating polio this year.
The anti-polio campaign hit a wall in June 2012, when the Pakistani Taliban banned vaccinations in the tribal belt, saying the restriction would last till US drone strikes cease.
Militants and gunmen have frequently attacked vaccination teams, accusing them of being Western spies and part of a plot to "sterilise" Muslims.