"The new case has been detected in North Waziristan where we had been denied access in June last year," the World Health Organization's senior coordinator for polio eradication in Pakistan, Elias Durry, told AFP.
Tribesmen in North Waziristan, Pakistan's most notorious stronghold of Taliban and Al-Qaeda linked militants, endorsed the Taliban ban and stopped authorities from vaccinating children under a nationwide campaign.
"This has been the first case since we were stopped from vaccinating children in the region last year," Durry said.
The Taliban alleged that the campaign was a cover for espionage.
Efforts to tackle the highly infectious disease have been hampered over the years by local suspicion about vaccines being a plot to sterilise Muslims, particularly in Pakistan's conservative and poorly educated northwest.
"We are worried because this new case comes as an example of a bigger impending outbreak of disease in the region," the WHO official said.
Pakistan, Afghanistan and Nigeria are the only three countries in the world where the highly infectious, crippling disease remains endemic and infections shot up from a low of 28 in 2005 to almost 200 last year.
Durry said the United Nations and the Pakistani government are working together to reach out to the children in North Waziristan.