Authorities in Pakistan said seven police officers have been killed, three of which were guarding polio workers, after gunman open fired on the group.
Eight gunman on motorcycles open fired at a group of three of the officers and later at a van carrying four others.
The opposition to vaccinating children under an extremist belief system is not new to Pakistan. Militants believe it is a Western conspiracy to sterilise children through these vaccination programs.
In 2014 Pakistan recorded over three hundred cases of polio and is one of two countries where polio remains an epidemic.
Sindh police Inspector General AD Khawaja told reporters polio drops would be “administered to our children at all costs” and that security for the polio teams would be increased.