Measles is not often seen in the United States, but Americans are growing more concerned about the preventable virus as cases continue to rise in rural West Texas.

Last week, an unvaccinated child died in the outbreak, which involves nearly 200 cases.

The U.S. Centers for Disease Control and Prevention said the last confirmed measles death in the United States was in 2015. The agency on Tuesday posted a message on X saying that “CDC is on the ground in TX,” indicating that the state had requested federal assistance in investigating and controlling the outbreak.

Here’s what to know about the measles and how to protect yourself.

Where Have Measles Cases Been Reported in the U.S.?

Besides Texas, which has had the most measles cases of any U.S. state this year, there are also 30 cases in New Mexico. The state health department there has said there is no direct connection to the outbreak in Texas.

Measles cases also have been reported in Alaska, California, Georgia, Kentucky, New Jersey, New York, Pennsylvania and Rhode Island.

The CDC defines an outbreak as three or more related cases. Three measles clusters have qualified as outbreaks in 2025, the agency said. In the U.S., cases and outbreaks are generally traced to someone who caught the disease abroad. It can then spread, especially in communities with low vaccination rates.

What Is Measles?

It’s a respiratory disease caused by one of the world’s most contagious viruses. The virus is airborne and spreads easily when an infected person breathes, sneezes or coughs. It most commonly affects kids.

“On average, one infected person may infect about 15 other people,” said Scott Weaver, a center of excellence director for the Global Virus Network, an international coalition. “There’s only a few viruses that even come close to that.”

Measles first infects the respiratory tract, then spreads throughout the body, causing a high fever, runny nose, cough, red, watery eyes and a rash.

The rash generally appears three to five days after the first symptoms, beginning as flat red spots on the face and then spreading downward to the neck, trunk, arms, legs and feet. When the rash appears, the fever may spike over 104 degrees Fahrenheit, according to the CDC.

There’s no specific treatment for measles, so doctors generally try to alleviate symptoms, prevent complications and keep patients comfortable.

People who have had measles once can’t get it again, health officials say.

Related Story: Measles: What to Know and How to Avoid One of the World’s Most Contagious Viruses

Can Measles Be Fatal?

It usually doesn’t kill people, but it can.

Common complications include ear infections and diarrhea. But about 1 in 5 unvaccinated Americans who get measles are hospitalized, the CDC said. Pregnant women who haven’t gotten the vaccine may give birth prematurely or have a low-birthweight baby.

Among children with measles, about 1 in every 20 develops pneumonia, the CDC said, and about one in every 1,000 suffers swelling of the brain called encephalitis — which can lead to convulsions, deafness or intellectual disability.

It’s deadly “in a little less than 1% of cases, mainly in children,” said Weaver, who works at the University of Texas Medical Branch in Galveston. “Children develop the most severe illness. The cause of death in these kinds of cases is usually pneumonia and complications from pneumonia.”

How Can You Prevent Measles?

The best way to avoid measles is to get the measles, mumps and rubella (MMR) vaccine. The first shot is recommended for children between 12 and 15 months old and the second between 4 and 6 years old.

“Before a vaccine was developed in the 1960s, everybody got” measles, Weaver said. “But then when the vaccine came along, that was a complete game-changer and one of the most successful vaccines in the history of medicine.”

There is “great data” on the safety and effectiveness of the vaccine, he said, because it’s been around for decades.

“Any of these outbreaks we’re seeing can easily be prevented by increasing the rate of vaccination in the community,” he said. “If we can maintain 95% of people vaccinated, we’re not going to see this happening in the future. And we’ve slipped well below that level in many parts of the country.”

Vaccination rates have declined nationwide since the COVID-19 pandemic, and most states are below the 95% vaccination threshold for kindergartners — the level needed to protect communities against measles outbreaks.

Related Story: First Measles Death Reported in Texas as Cases Surpass 120

Do You Need a Booster if You Got the MMR Vaccine a While Ago?

Health care professionals are sometimes tested for antibodies to measles and given boosters if necessary, Weaver said — even if they’ve already had the standard two doses as a child.

Adults with “presumptive evidence of immunity” generally don’t need measles shots now, the CDC said. Criteria include written documentation of adequate vaccination earlier in life, lab confirmation of past infection or being born before 1957, when most people were likely to be infected naturally.

Also, people with documentation of receiving a live measles vaccine in the 1960s don’t need to be revaccinated, the CDC added. However, those immunized before 1968 with an ineffective measles vaccine made from “killed” virus — or people who don’t know which type they got — should be revaccinated with at least one dose, the agency said.

Weaver said people at high risk for infection who got the shots many years ago may want to consider getting a booster if they live in an area with an outbreak. Those may include family members living with someone who has measles or those especially vulnerable to respiratory diseases because of underlying medical conditions.

“I don’t think everyone needs to go and run out to their doctor right now if they did receive two doses as a child,” he said. “If people would just get the standard vaccination, none of this would be happening.”

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Educational Media Group and the Robert Wood Johnson Foundation. The AP is solely responsible for all content.