Three anti-polio campaign members were hit by a remote-controlled blast in Mamond area of Bajaur in Federally Administered Tribal Areas (FATA), one of the seven districts where Taliban is active.
An official from the political agent office said that the injured were shifted to a hospital in the town of Khar where they were said to be in stable condition.
The attack came just a day after militants had openly threatened anti-polio workers of targeted attacks if they continue to participate in the ongoing polio drive.
Militants in Pakistan's tribal region are vehemently opposed to anti-polio medicine and often see it as a conspiracy by the west to sterile Muslims.
The latest attack on immunisation teams comes as Pakistan broke its 13-year-old record of highest number of polio cases in a year on October 3. As many as 207 children in Pakistan have already been infected by the crippling virus in 2014, with an overwhelming 96 per cent cases reported from the tribal regions of Khyber Pakhtunkhwa and FATA.
A recent World Health Organisation report described Pakistan as the "greatest single risk" to eradicating the disease, saying it accounts for nearly 80 per cent of the polio cases globally.