Police said the attackers fired indiscriminately after entering the Matni Hospital and then fled the scene, Pakistan's Dawn News reported.
A polio worker was killed immediately. An orderly and a woman were severely injured.
No group claimed responsibility for the attack, but several polio workers and the police protecting them have killed in recent attacks by militants.
Pakistan is one of only three countries where polio is endemic.
Celebrity Couples of 2014 [PHOTOS]