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Although measles was considered eliminated in the United States in 2000, measles cases have surged over the past few years, with 2026 expected to be one of the worst in recent history. We’re just a few months into the year, but the number of confirmed measles cases in the country so far is about half of last year’s (also very high) total.
You probably know that measles is a virus you don’t want to get, but it’s understandable to be fuzzy on the details. Thanks in large part to very effective childhood vaccines, most adults don’t think much about measles in their daily lives. But recent news reports and rising case numbers may still influence who gets vaccinated.
Here’s what infectious disease doctors want you to know about measles, what the vaccine prevents, and potential complications.
Meet the experts: Thomas Russo, MD, Professor and Director of Infectious Diseases, University at Buffalo, New York; William Schaffner, MD, Infectious Disease Specialist, Professor at Vanderbilt University School of Medicine; Amesh A. Adalja, MD, Senior Scholar, Johns Hopkins University Center for Health Security
What is measles?
Measles, also known as rubella, is a highly contagious viral infection. It causes a cough, runny nose, small spots in the mouth, rash, and often a high fever. Measles can also cause serious complications, such as pneumonia, immune amnesia, and encephalitis (or brain swelling).
The World Health Organization considers measles one of the most contagious diseases in the world. It is spread through contact with respiratory droplets. According to the World Health Organization, the virus can remain active and contagious in the air or on surfaces for up to two hours.
“Because we haven’t seen a lot of measles here in a while, [some assume] It’s just a minor illness with a rash,” said William Schaffner, MD, Infectious disease specialist and professor at Vanderbilt University School of Medicine. “That’s not true. Before vaccination in the United States, 400 to 500 children died from measles and its complications every year.”
What does the latest data show?
It’s worth noting that measles cases occur every year in the United States, even after the virus is thought to have been eradicated. But the number of cases has been unusually high in recent years. According to CDC data, there have been 1,136 confirmed cases of measles so far in 2026, with cases in 28 states. The CDC notes that the actual number is likely higher because these 1,136 cases are just Confirmed Example.
Ten new measles outbreaks were reported this year and the majority (90%) of cases were associated with these outbreaks. (Amesh A. Adalja, MD, senior scholar at the Johns Hopkins University Center for Health Security, explained that a classic example of a non-outbreak-related case would be an international traveler to the United States who came down with measles.) Notably, South Carolina’s outbreak has made national and international headlines over the past month.
What does the rise in measles cases mean for people?
A lot depends on your vaccination status. Unvaccinated people living during an outbreak are more likely to get measles and get sick. They may also be more likely to develop infection-related complications.
It’s a different story if you’re vaccinated. According to the CDC, the measles vaccine is 97% effective at preventing infection when you receive two doses of the vaccine. “The measles vaccine is one of the best vaccines we have,” Schaffner said. “The vast majority of people who are vaccinated against measles will not have any problems if exposed to measles,” Adalja added.
But Dr. Thomas Russo, a professor and chief of infectious diseases at the University at Buffalo in New York, pointed out that 97% is not 100%, which still opens the door to potential infection even for those who have been vaccinated. “However, if you are vaccinated, the disease tends to be much milder.”
In the event of a severe outbreak, such as the one in South Carolina, schools may quarantine after exposure, Adalja said. Adalja said the CDC also requires measles cases to be reported to public health departments for further investigation, which could divert resources from other issues.
Who is most likely to get measles?
Russo explained that people who are unvaccinated and undervaccinated (meaning they have only received one of two doses of vaccine) are most at risk. This includes young children and immunocompromised children who are not yet eligible for vaccination. He pointed out that because the measles vaccine is a live attenuated vaccine, not everyone can get it. “That’s why, as a community, we want to work to increase vaccination rates,” Russo said.
What are the complications of measles?
Measles can cause a complication called immune amnesia, which affects the body’s ability to respond to pathogens it has previously been exposed to, Adalja said. Studies show that the measles virus can eliminate 11 to 73 percent of the antibodies a person produces to protect themselves against viral and bacterial strains. This means that previous immunity to illnesses such as the flu, COVID-19, chickenpox, etc. may be suddenly lost, increasing the risk of future illness.
“This can happen to some degree in everyone who gets measles,” Adalja explained. While it’s unclear how long immune amnesia lasts, data suggests it could last two to three years. (That said, Adalja says there are no routine recommendations for revaccination of childhood vaccines.)
Encephalitis is another serious complication of measles. It can cause brain swelling and can even be fatal. “Even if children recover, they may be left with disabilities,” Schaffner said.
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If you’re fully vaccinated against measles, you usually don’t need to do anything different. “If you are vaccinated and exposed, it is not recommended that you quarantine,” Russo explained. However, that’s different if you’re unvaccinated or under-vaccinated, in which case call your healthcare provider for next steps.
Experts also stress the importance of getting vaccinated if you haven’t been vaccinated against measles or are under-vaccinated. “The number of cases in the United States is a choice,” Adalja said. “Measles solutions have been around for decades. People are choosing to abandon those solutions.”
Schaffner agrees. “Measles is a nasty virus,” he said. “It’s worth preventing. I wouldn’t even want any child to get simple measles.”
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