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The measles outbreak that began in west Texas in late January 2025 continues to grow, with and more than 50 in and as of March 28.

Public health experts believe the numbers are much higher, however, and some worry about a in the U.S. In the past two weeks, health officials have identified potential measles exposures , including and on an – as well as at health care facilities where the infected people sought medical attention.

Measles infections can be extremely serious. So far in 2025, . Last year, that number was 40%. Measles can damage the lungs and immune system, and also inflict permanent brain damage. Three in 1,000 people who get the disease die. But because measles vaccination programs in the U.S. over the past 60 years , few Americans under 50 have experienced measles directly, making it easy to think of the infection as a mere childhood rash with fever.

As a biologist who studies , I believe it is important for people to understand how dangerous a measles infection can be.

Underappreciated Acute Effects

Measles is one of the most contagious diseases on the planet. One person who has it will infect if those people are unvaccinated. A two-dose regimen of the vaccine, however, is .

When the measles virus infects a person, it binds to specific proteins on the . It then inserts its genome and replicates, destroying the cells in the process. This first happens in the upper respiratory tract and the lungs, where the virus can damage the person’s ability to breathe well. In both places, the virus that carry it to the lymph nodes, and from there, .

Measles can wipe out immune cells’ ability to recognize pathogens.

What generally lands people with measles in the hospital is the disease’s effects on the lungs. As the virus destroys lung cells, , which is characterized by severe coughing and difficulty breathing. Measles pneumonia afflicts and is the most common cause of death from measles in young children.

The virus can and also damage it by causing inflammation. Measles can cause : a direct infection of the brain that occurs in roughly 1 in 1,000 people, or inflammation of the brain two to 30 days after infection that occurs with the same frequency. Children who survive these events and impairments such as and .

Yearslong Consequences of Infection

An especially alarming but still poorly understood effect of measles infection is that it can reduce the it has previously encountered. Researchers had long suspected that children who get the measles vaccine also tend to , but they were not sure why. A study published in 2019 found that having a measles infection , leaving them vulnerable to many of the infections to which they previously had immunity. This effect, called immune amnesia, lasts until people are reinfected or revaccinated against each disease their immune system forgot.

Occasionally, the virus can lie undetected in the brain of a person who recovered from measles and . This condition, called , is a progressive dementia that is almost always fatal. It occurs in about 1 in 25,000 people who get measles but is about five times more common in .

Researchers long thought that such infections were caused by a , but more recent research suggests that the measles virus can acquire mutations that enable it to infect the brain .

There is still much to learn about the measles virus. For example, researchers are exploring . However, even if such treatments work, the best way to prevent the serious effects of measles is to avoid infection by getting vaccinated.

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