Nigeria is launching an emergency polio vaccination program after two infants were found to have contracted the disease in the far-flung northeastern state of Borno, the country's first two cases in more than two years.

Military helicopters are airlifting the vaccine to the affected region, but carrying out the inoculations won't be easy. The radical Islamist group Boko Haram controls or threatens much of the area.

The group has been known to kill health workers carrying out the vaccinations. But the militant group has lost territory in recent months, and the government is determined to push ahead with the vaccination effort.

The Nigerian government has "moved into emergency outbreak response mode," UNICEF spokesperson Priyanka Khanna said in a statement.

"Planning for a large-scale campaign is in place," Khanna said. "The first campaign will start on August 27, targeting 1.3 million children. Subsequently two further rounds will be conducted, at two-to-three week intervals, reaching four-to-five million children."

The latest cases are a major setback for Nigeria, which was on track to be certified free of the illness in 2017. The World Health Organization (WHO) removed Nigeria from its polio-endemic List in 2015, meaning that all of Arica was free of the disease. The only two other countries that remain on the list are Pakistan and Afghanistan.

Aid convoy attacked

But even with the support of the WHO and the US Centers for Disease Control, Nigeria faces considerable obstacles in an area where the UN suspended aid last month after a military-escorted humanitarian convoy was attacked.

"Not all the areas that have been liberated by the military could be accessed by our health officials because of recent attacks in Jere and Gwoza local government areas carried out by Boko Haram," said Ibrahim Miringa, a Borno state health commissioner.

The new immunization plan calls for international organizations to support Nigerian health workers using "a hit-and-run strategy," according to the WHO director for polio eradication, Dr. Michael Zaffran.

After starting in Nigeria's Borno state, the large-scale vaccination drive will extend into nearby Benin, Chad, Central African Republic and Cameroon, Zaffran said.

The WHO said the new cases indicate the virus has circulated undetected in Borno state for the past five years.

Polio is an infectious viral disease that primarily affects children and can lead to permanent paralysis. There is no cure for the disease and it can only be prevented via immunization.

bik/cmk (AP, AFP)