A child cries after she was administered a polio vaccine during a house-to-house vaccination exercise in Maiduguri, Nigeria. (Sunday Alamba/AP)

An emergency polio vaccination campaign aimed at reaching 25 million children this year has begun in parts of Nigeria newly freed from Boko Haram Islamist extremists, with fears that many more cases of the crippling disease will probably be found.

Two toddlers diagnosed last month were Nigeria’s first reported polio cases in more than two years, putting the world on alert just months after the African continent was declared free of the disease.

Just 20 years ago, this West African nation was considered the world’s epicenter of polio, recording 1,000 cases a year. Men and women with twisted limbs crawling along the roadside to beg remain a common sight. A global drive to end polio began in 1988, when the highly contagious disease was endemic in 125 countries. Polio persists in only two other countries: Pakistan and Afghanistan.

Health workers, using military helicopters, all-terrain vehicles and even tricycle taxis, vaccinated about 1.5 million children in the past week, starting in the refugee camps where the new cases surfaced.

A health official administers a polio vaccine to children at a camp for people displaced by Islamist Extremist in Maiduguri, Nigeria. (Sunday Alamba/AP)

The World Health Organization has said that the two new cases indicate that the wild polio virus has been circulating for five years in northeastern Borno state, where Boko Haram began its uprising in 2009.

More cases are expected to surface as Nigeria’s military ­forces Boko Haram out of more towns and villages, said Tunji Funsho, head of Rotary Club’s “End Polio Now” eradication drive.

The Islamist group, which took over portions of the country, violently opposes Western medicine or culture, making it impossible to vaccinate those living under its rule. Boko Haram’s opposition to all things Western reached new heights in 2013, when militants fatally shot nine women vaccinating children against polio in northern Kano, Nigeria’s second-largest city.

“Boko Haram is largely responsible for the insecurity that has hamstrung vaccination efforts in Nigeria,” a new report from U.S.-based risk-analysis group Stratfor said. “Though the group has weakened since the start of 2015 . . . as long as this security risk remains, so, too, will the risk that Nigeria’s latest run-in with polio will not be its last.”

Boko Haram is in retreat but remains deadly. In July, militants attacked a humanitarian convoy near Maiduguri, the region’s largest city, leading the United Nations to suspend aid to newly liberated areas where it says half a million people are starving.

Over the years, the vaccination campaign has also had to fight rumors that the vaccine was a plot to sterilize Muslims, which it overcame by winning over religious and traditional leaders and grass-roots women’s groups.

People displaced by Islamist Extremist fetch water at Muna camp in Maiduguri, Nigeria. (Sunday Alamba/AP)

“Yes, it’s a major setback, but we are not defeatist,” Funsho declared of the latest cases. He looked over a map of Borno state that showed only a small southern section as “accessible,” most of the sprawling state “partially accessible” and a band in the north bordering Niger, Cameroon and Chad as “inaccessible” because of Boko Haram fighters.

Over the past week, hundreds of health workers from the government, the United Nations and aid organizations spread out across Borno state, delivering the vaccinations through drops on the tongue.

Military armored cars and truckloads of soldiers guarded trips into precarious areas. They included the town of Chibok, where nearly 300 schoolgirls were kidnapped in April 2014, shocking the world. More than 200 remain missing. Boko Haram extremists attacked a village near Chibok last week, killing 11 people.

For areas too dangerous to reach by road, helicopters delivered vaccines to already trained people on the ground, to avoid suspicion of strangers, said Rotary field coordinator Aminu Muhammad.

“We’ve even been able to reach a couple of areas that we had been told by the military were inaccessible, after community leaders informed us we could get through,” Muhammad said. “Still, there were some major communities outside the metropolitan areas that we were unable to reach.”

Muhammad could not estimate costs for the massive campaign because organizations such as the U.S. Centers for Disease Control and Prevention, the U.N. children’s agency and London-based Save the Children all are participating with their own budgets.

Most vaccinators are women, because men traditionally are not allowed into the home of a Muslim woman if her husband is absent.

One campaign member, Maryam Kawule of the Core Group, led green-veiled young women ticking off family names handwritten in an exercise book. “We do the preliminary work of counting the children, and we’re here now to ensure every kid under 5 gets his or her vaccination,” she said.

It doesn’t end there. The polio vaccine has to be administered at least three times to each child, and up to five times in endemic areas, so more rounds are planned next year.

— Associated Press