The Philippines, which has more than 2.4 million children who aren’t vaccinated against measles, declared an outbreak of the disease on Tuesday following nearly 2,000 cases and 26 deaths since Jan. 26. In Madagascar, more than 50,000 people have been infected by the disease since October — more than the total number of reported cases throughout Africa in 2018. And in Europe, measles cases tripled between 2017 and 2018, according to the World Health Organization.

All around the world, measles appears to be making a dangerous comeback, endangering millions of children. The ongoing spike is primarily driven by a large numbers of unvaccinated people.

In developing countries, poor access to health care means people are not able to get or afford vaccines, allowing infectious diseases like measles to spread rapidly. In wealthier countries where health care services tend to be more accessible, misinformation spread by the “anti-vaxxer” movement questioning the safety of vaccines has deterred many parents from immunizing their children.

In the US, for example, Washington state was forced to declare a public health emergency last month, following a measles outbreak driven by a high number of parents refusing to vaccinate their children.

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“The increase in measles cases is deeply concerning, but not surprising,” said Dr. Seth Berkley, CEO of Gavi, the Vaccine Alliance, in a press release.

“Complacency about the disease and the spread of falsehoods about the vaccine in Europe, a collapsing health system in Venezuela and pockets of fragility and low immunization coverage in Africa are combining to bring about a global resurgence of measles after years of progress,” he added.

Measles is a highly infectious disease that mainly affects children. Although its symptoms can, at first, be hard to distinguish from the common cold, it can rapidly escalate, causing encephalitis, deafness, and even death.

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Before the measles vaccine was introduced in 1963, measles was the leading killer of children around the world. Today, measles kills around 100,000 people, mostly children, per year.

What makes the recent spread of measles particularly vexing to health officials is that it can be easily prevented through vaccinations. By the turn of the 21st century, rising vaccination rates seemed to forecast the eventual elimination of the disease.

But the progress that has been made is now in jeopardy.

The WHO urges countries to vaccinate at least 95% of its citizens to generate “herd immunity,” which is when enough people are immunized against a disease to effectively prevent it from spreading and causing an outbreak.  

Madagascar currently has an immunization rate below 50% and the Philippines has seen immunization plummet to around 60% in recent years. Immunization rates in countries like the US and Italy have been steadily declining for years.

The WHO and other health organizations are working with countries experiencing measles outbreaks to contain the disease. These groups are calling for greater investment in immunization systems, more resources dedicated to vaccination services, and public health campaigns to counter the spread of misinformation.

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“Existing strategies need to change,” Berkley said in the press release. “More effort needs to go into increasing routine immunization coverage and strengthening health systems. Otherwise we will continue chasing one outbreak after another.”