(CNN) - Polio has been declared eradicated from Africa, the World Health Organization announced Tuesday.
"Today we come together to rejoice over a historic public health success, the certification of the eradication of wild poliovirus in the African region," said Tedros Adhanom Ghebreyesus, director general of the World Health Organization, during a live-streamed event.
"The end of wild polio in Africa is a big day," said Tedros, who is also the chairman of the Polio Oversight Board. «Your success is the success of the world. None of us could have done this alone.
Polio was once a common virus. In some young children it can affect the nerves and cause muscle weakness or paralysis. There is no treatment or cure, but getting vaccinated can prevent infection.
- LOOK: A vaccine against polio that already exists could help protect against the coronavirus
Governments and non-profit organizations have worked since 1996 to try to eradicate the virus from the African continent with sustained vaccination campaigns. Nearly 9 billion polio vaccines have been delivered, according to Tedros.
A large part of the eradication effort has been carried out through the Global Polio Eradication Initiative (GPEI), which was created in 1988 and is led by national governments and five partners: Rotary International, WHO , UNICEF, the US Centers for Disease Control and Prevention, and the Bill and Melinda Gates Foundation.
US Secretary of Health and Human Services Alex Azar, US Centers for Disease Control and Prevention Director Dr. Robert Redfield, and Bill and Melinda Foundation Co-Chair Gates, Bill Gates, congratulated Africa on eradicating polio during the certification event for this milestone on Tuesday.
"Today is a historic day for world health and is a cause for celebration for all who work to improve the health of Africans," Azar said in a prerecorded message. "Congratulations to everyone who helped make it possible."
Officials wanted to make sure the polio really did go away and have waited four years since the last case of the wild virus was diagnosed.
Rose Gana Fomban Leke, president of the African Regional Commission for Certification for the Eradication of Polio, told CNN that the decision to declare the region free of the virus came after many years of surveillance, immunization and laboratory analysis by the poliomyelitis in the 47 member states of the region on the continent.
“The work has continued for years and now we can see the results. It is a huge milestone. I am sure I can say that in the region, during the last four years, we have not seen a single poliovirus, "she said.
According to a WHO statement, “The last case of wild poliovirus in the region was detected in 2016 in Nigeria. Since 1996, polio eradication efforts have prevented up to 1.8 million children from paralysis for life and saved approximately 180,000 lives.
This does not mean that no child will develop polio symptoms. The weakened virus used to make the oral vaccine can sometimes survive in populations that are not immunized and, if it circulates long enough, it can revert back to a dangerous form. It's called a vaccine-derived acirculating poliovirus. The WHO says 16 African countries are currently fighting outbreaks of this vaccine-derived strain.
"The small risk of circulating poliovirus derived from the vaccine pales in the face of the enormous public health benefits associated with oral polio vaccine," says the WHO on its website.
“Hundreds of thousands of cases due to the wild polio virus are prevented each year. More than 10 million cases have been prevented since the large-scale administration of the oral polio vaccine began 20 years ago.
- MORE: Children under 5 should not wear masks, says WHO
That is why children in developing countries receive two doses of the vaccine: the oral vaccine, which is given in easy-to-give drops, and an injection, which is made with a completely inactivated polio virus that cannot be reactivate. Children in developed countries only receive the vaccine, but they need four doses to be fully protected.
“In the past, circulating vaccine-derived polioviruses were quickly stopped with two or three rounds of high-quality immunization campaigns. The solution is the same for all polio outbreaks: immunize all children several times with the oral vaccine to stop the transmission of polio, regardless of the origin of the virus, "said WHO.
The last region to eradicate wild polio was Southeast Asia. Polio has been eradicated in the Americas, Europe, most of Australasia, and now Africa. Wild polio strains now only circulate in two countries: Afghanistan and Pakistan.
"Wild poliovirus cases have decreased by more than 99% since 1988, from an estimated 350,000 cases in more than 125 endemic countries at that time, to 175 cases reported in 2019," the WHO noted.
Bill Gates, founder of Microsoft and co-chairman of the Bill and Melinda Gates Foundation, called it a "historic milestone and a public health triumph for Africa."
But he cautioned that it is important now more than ever to protect the progress made. Wild polio is still present in Pakistan and Afghanistan, and until it disappears everywhere, it can still return, he said.
Redfield of the CDC in the US also noted that there is still work to be done. He said that each country must continue to vaccinate to maintain high levels of protection against vaccination.
"This is Africa's time to celebrate and savor, and I want you to know that the CDC is with you today, until the day polio is finally eradicated," Redfield said in a pre-recorded interview.
"They have shown how much can be achieved when determination, partnership and resources come together, no matter the circumstances," he said.
WHO Polio