Once measles threatens a community, there’s only one surefire way to stop its spread — vaccines.

Thanks to vaccines, doctors and public health workers have been able to halt the spread of measles and save millions of lives. Last year, for the first time in history, the number of people who died from measles dropped below 100,000, the World Health Organization reports.

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In 2016, measles killed about 90,000 people, a new report by top health agencies revealed. The death toll is still high, but it marks an 84% decrease since 2000 when measles killed more than 550,000 people.

According to the Measles & Rubella Initiative (M&RI), the decreasing death rate is due to aggressive worldwide vaccination campaigns that reach more and more children every year.  The MR&I is a partnership among various top health agencies including the American Red Cross, the US Centers for Disease Control and Prevention, the United Nations Foundation, UNICEF, and the World Health Organization. The agencies joined forces in 2001.

The United Nations says that about 5.5 billion measles vaccines delivered to children have saved an estimated 20.4 million lives since 2000.

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Despite the positive news, public health workers say they still have a lot of work to do.

Measles begins with a fever, cough, and a tell-tale splotchy rash but can quickly worsen, causing pneumonia, brain swelling, and even death. The highly contagious illness can spread rapidly through communities and is particularly dangerous for young children.

20.8 million children are still missing their first measles vaccine dose, WHO says. More than half of the unvaccinated children live in just six countries in Africa and Asia: Nigeria, India, Pakistan, Indonesia, Ethiopia, and Democratic Republic of the Congo.

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Earlier this month, New Zealand announced that it had officially eliminated measles and the majority of European countries have also prevented the spread of measles, WHO reported. However, in the United States, some parents have avoided vaccinating their children for fear that the vaccines cause autism — a widespread myth — leading to outbreaks of the airborne illness in some communities.

“We have seen a substantial drop in measles deaths for more than two decades, but now we must strive to reach zero measles cases,” said Dr Jean-Marie Okwo-Bele, the director of WHO’s Department of Immunization, Vaccines and Biologicals. “Measles elimination will only be reached if measles vaccines reach every child, everywhere.”