LAGOS, Nigeria (AP) — Once stigmatized as the world’s polio epicenter, Nigeria on Friday celebrates its first year with no reported case of the crippling disease, having overcome obstacles ranging from Islamic extremists who assassinated vaccinators to rumors the vaccine was a plot to sterilize Muslims.

Just 20 years ago this West African nation was recording 1,000 polio cases a year — the highest in the world. The last recorded case of a child paralyzed by the wild polio virus endemic in Nigeria’s impoverished and mainly Muslim north was on July 24, 2014.

“We are celebrating the first time ever that Nigeria has gone without a case of polio, but with caution,” Dr. Tunji Funsho, chairman of Rotary International’s polio campaign in Nigeria, told The Associated Press.

If there are no new cases and laboratory tests remain negative in the next few weeks, the World Health Organization will take Nigeria off the list of polio-endemic countries, said Oliver Rosenbauer of the U.N. agency’s polio unit.

Nigeria is the last African country on that list.

The two remaining countries are Pakistan, which recorded 28 new cases this year, and Afghanistan, with five, said Rosenbauer. It’s a 99 percent reduction since the Global Polio Eradication Initiative began in 1988, when one of the world’s most feared diseases was endemic in 125 countries and was paralyzing nearly 1,000 children every day.

Polio shows up unsuspiciously as a fever and cold, followed quickly by acute paralysis as the virus destroys nerve cells. The disease mainly affects children under 5. The virus invades the body through the mouth and multiplies in the intestine, then is spread through the feces. It is highly contagious with infected but asymptomatic carriers able to spread it silently and swiftly.

That’s why “surveillance takes place in every nook and cranny of this country, even in those areas that have been free for years,” said Rotary’s Funsho.

In Nigeria, where Boko Haram Islamic extremists held a large swath of the northeast for months until March, that means testing sewage and stool samples of refugees from areas too dangerous to access.

The extremists opposed the campaign and Boko Haram gunmen killed nine women vaccinators in northern Kano state in February 2013, but the vaccinations continued.

The milestone has been reached despite the government’s failure to deliver the most basic services: 100 million of Nigeria’s 170 million people defecate in the open, while the percentage with piped water has shrunk from 12 percent in 1990 to 2 percent today, according to U.N. estimates.

Nigeria has been on the brink of recording no new cases before, only to fall back during elections in 2007 and 2011 when money was lavished on political campaigns instead of vaccinations, said Dr. Oyewale Tomori, chairman of the government’s Expert Review Committee on Polio Eradication.

Politicians spent unprecedented amounts on March elections that for the first time ousted a sitting president. But 2015 also brought the government’s biggest commitment of $80 million to fight polio.

Flexible strategy was needed for the campaign to succeed. “Initially there was this wrong approach … we thought we could overcome it with global pressure and scientific information,” Tomori said. “It didn’t work.”

The campaign had to win over religious and community leaders and grass-roots women’s groups, he said.

Nigeria tracks vaccinators through GPS on their cell phones and has emergency operations centers that provide “real-time information,” said Tomori. “If someone refuses vaccination, we know within minutes and can go back and take action. Before, it could take weeks.”

The polio tracking system has additional benefits. It formed the backbone of Nigeria’s successful efforts to fight Ebola.

The WHO will not declare Nigeria out of the woods until 2017.

“It will take another two extra years of no polio to be polio-free and that is why we cannot relax,” said Tomori, who has been fighting polio for 20 years.

He said monitoring, surveillance and vaccinations all must increase to ensure no backsliding: “On no account must we lose focus and take our eye off the polio radar.”