The first attack took place in the Gulshan-e-Bunir area where armed men attacked a team of female workers who were going to administer the anti-polio vaccine drops and shot them dead.
The workers were identified as Naseem and Kaneez.
In the second incident that took place half-an-hour later in Orangi, armed men shot at a female and male worker killing them both.
The World Health Organisation in reaction to the killings immediately announced the suspension of the anti-polio vaccine campaign in Karachi.
"We have informed the Sindh provincial government of our decision to suspend the campaign," a WHO spokesman said.
On Monday a worker of the anti-polio campaign was also attacked in Sohrab Goth while he was returning home.
Militant groups have openly opposed the anti-polio campaign in the country as some groups describing it as anti-islamic.
