African leaders said Tuesday the continent is free of wild poliovirus, a historic public health achievement that will spare tens of thousands of children from the devastating disease every year.

The Africa Regional Certification Commission for Polio Eradication officially declared the continent free of polio, four years after Nigeria reported the last known case.

“This is a momentous milestone for Africa. Now future generations of African children can live free of wild polio,” said Matshidiso Moeti, the World Health Organization’s Africa regional director.

Poliovirus paralyzed an estimated 75,000 African children annually in the 1990s, when African nations began their push to eradicate the virus. Then-South African President Nelson Mandela kicked off the continentwide effort to end infections in 1996.

Polio has not completely ended in Africa. Sixteen countries are still battling outbreaks of circulating vaccine-derived poliovirus, according to the World Health Organization. That type can occur in under-immunized populations when particles of virus used in vaccines mutate to cause paralyzation.

Those mutations are extremely rare. Since 2000, more than 10 billion doses of oral polio vaccine have been administered, and just 760 cases of vaccine-derived virus have been identified.

World Health Organization officials said they were confident that continued surveillance and vaccination could completely eliminate even the vaccine-derived cases.

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