ARI SHAPIRO, HOST:

The continent of Africa is now free of wild polio, the virus that occurs naturally in the environment. As NPR's Eyder Peralta reports, this is a huge public health victory decades in the making.

EYDER PERALTA, BYLINE: For years, health workers had to go into some of the most dangerous places in Africa to deliver vaccines. In Nigeria, they ventured into insurgent territory just after bomb blasts to deliver vaccines to children. On Aug. 21, 2016, Nigeria detected the last case of wild polio on the continent. Today, the Africa Regional Certification Commission declared the continent free of wild polio. Dr. Matshidiso Moeti of the World Health Organization credits the huge effort of local health workers and the international community.

MATSHIDISO MOETI: It is a vivid reminder that vaccines work and that the collective actions of communities, governments and partners can bring about tremendous changes.

PERALTA: But African countries still face a threat - vaccine-derived polio. In communities with low vaccination rates, the weakened virus in the oral vaccines can circulate and, in rare cases, mutate into a virus that causes paralysis just like wild polio. Still, this is a historic achievement. In 1996, Nelson Mandela launched the Kick Polio Out of Africa campaign. Since then, health workers have administered billions of doses of the vaccine in cities and remote villages and refugee camps. The head of the WHO, Dr. Tedros Adhanom Ghebreyesus, says at times, a polio-free world seemed impossible.

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TEDROS ADHANOM GHEBREYESUS: But in the words of Nelson Mandela, when people are determined, they can overcome anything.

PERALTA: Wild polio is still present in Afghanistan and Pakistan. But today, we're one step closer to a world without polio.

Eyder Peralta, NPR News, Nairobi. Transcript provided by NPR, Copyright NPR.