A health official administers a polio vaccine to a child in Kawo Kano, Nigeria, Sunday, April. 13, 2014. Nigeria is one of three countries in the world where the wild polio virus remains endemic. (Sunday Alamba/AP)

| From staff reports and news services

Nigeria has reported its first two cases of polio in more than two years, in an area newly liberated from Islamist extremists who had attacked polio vaccinators in the past, the government and the World Health Organization said Thursday.

Nigeria’s removal from the WHO’s list of polio-endemic countries in October had meant the entire African continent was free of the crippling disease.

Tarik Jasarevic, a spokesman for the WHO, said in an email that “finding children paralyzed by polio shows that surveillance is working, even in areas of the country affected by insecurity, but it is a sobering reminder that countries need to remain vigilant and immunize children until the virus is completely eradicated worldwide.”

Two children have been paralyzed by polio in Nigeria’s northeastern Borno state in two local government areas that had been cut off by Boko Haram’s Islamist militants, Health Minister Isaac Adewole said in a statement Thursday night.

Adewole ordered the deployment of a national emergency response team. The WHO said it was working with the government to urgently use large-scale immunizations and other measures to prevent more children from being infected.

The U.S. Centers for Disease Control and Prevention issued a statement Thursday saying that “this is not the first time that polio eradication efforts have experienced a setback. It is a reminder that we must redouble efforts to strengthen surveillance and immunization activities. We remain 100 percent committed to eradicating polio.”

It was unclear how accessible the two areas in Nigeria are. The United Nations last month suspended aid to newly liberated but still dangerous areas of Borno after Boko Haram ambushed a humanitarian convoy, wounding three civilians, including a ­UNICEF worker. The suspension came even as aid groups declared that half a million people are starving in those areas and ­children are dying daily of starvation.

Because of the Islamist uprising in the country’s northeast, health workers have been testing sewage and stool samples of refugees from areas too dangerous to access.

Nigeria’s fight against polio has been dramatic. Two decades ago, it was recording 1,000 polio cases a year, the highest in the world.

The Islamist extremists opposed the anti-polio campaign. Boko Haram gunmen killed nine female vaccinators in ­northern Kano state in February 2013, but the vaccinations continued.