The two attackers on a motorbike opened fire on the team as they went to administer polio drops on the edge of the city of Peshawar, near the restive Khyber tribal region where the military has been battling homegrown insurgents with links to the Taliban.
"One lady worker was killed and another wounded in the attack on the first day of a three-day campaign meant for areas on the outskirts of Peshawar," local police official Shafi Ullah told AFP.
An official in the city's Lady Reading hospital confirmed the death.
No one has claimed responsibility for the killing. But last year the Pakistani Taliban banned polio vaccinations in the tribal region of Waziristan, alleging the campaign was a cover for espionage.
Late last year polio teams came under attack in Karachi and in the northwest, with nine health workers carrying out vaccinations killed by gunmen.
Pakistan, Afghanistan and Nigeria are the only countries where polio is endemic. Polio cases in Pakistan hit 198 in 2011, the highest figure for more than a decade and the most of any country in the world, according to the UN.
UN officials say there are about 161,000 children in North Waziristan district alone who have not received a polio vaccine since June last year.