The roadside bomb was detonated as the police-guarded convoy of polio vaccination workers drove through a village in Khyber Pakhtunkhwa province, the BBC reported.
Initial reports said the convoy hit two separate bombs on Saturday.
No group has claimed responsibility for the attack.
Assistant Political Agent Nasir Khan confirmed that 10 security personnel guarding the polio team were killed, along with one child, Dawn News reported.
This was the latest blow to the vaccination program in Pakistan, which militants have called a cover for espionage programs.
The World Health Organization said Pakistan is the world's "largest reservoir" of polio, with 91 cases of the crippling disease reported last year.
Neighboring India recently celebrated its third year without a single polio case being reported.
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