Measles is on the rise in the United States. As of May 22, 2025, the Centers for Disease Control and Prevention has reported 1,046 measles cases across the country with 14 outbreaks, with outbreaks being defined as having three or more measles-related cases. So far, 92% of these confirmed cases are outbreak related. For comparison, in 2024, only 69% of measles cases (198 of only 285) were outbreak related.
John Lednicky, Ph.D., a member of the University of Florida Emerging Pathogens Institute, explains the virus that has reemerged in clusters across 31 states, including Florida, Texas, California and New York. Lednicky, a professor at the UF College of Public Health and Health Professions, currently teaches a course on virology and public health, with his research focusing on virus discovery and surveillance, particularly on arthropod-borne viruses.
What follows is edited for length and clarity.
What is measles?
The measles virus is a fascinating example of how far public health has come. It’s classified as a “morbillivirus” — a name that aptly hints at its serious effects in the past. Not too long ago, measles was one of the leading causes of mortality among children in the United States. Fortunately, thanks to the invention of the vaccine in the 1960s, it’s highly preventable.
When humans first domesticated cattle roughly 5,000 years ago, a virus disease called rinderpest virus jumped species into humans. It became measles, which humans then transmitted to dogs, becoming canine distemper virus. Fun fact: Zoos sometimes give their animals the measles vaccine to protect them against canine distemper virus because the viruses are similar.
How does measles spread? Is the virus airborne?
Measles is spread through airborne routes, primarily through coughs and sneezes. To contract measles, you could inhale the virus, or it might come into contact with the mucus membranes of your nose, mouth or eyes.
Measles will affect your system and can cause serious complications. Like canine distemper virus, the thing to worry about the most is whether the virus gets into your brain. That’s when it can have very serious-to-deadly consequences, like SSPE, or subacute sclerosing panencephalitis — a progressive, deadly brain disorder.
Essentially, we don’t want to contract measles because so many things can happen. Luckily, it’s totally preventable; this is one of the diseases where the old vaccine still works, which is not very common.
Is measles highly transmissible?
I think the statement that measles is highly transmissible is likely a myth. The virus’s reproduction number — an estimate of how many people can get infected if they’re around a sick person — is all over the place. It ranges from three to over 200.
There are two issues with the myth. Number one is that measles tends to have very easily diagnosable symptoms — you get the rash inside your mouth, you cough and you sneeze. Number two, the outcome of a measles infection can result in severe complications like pneumonia, whereas with other respiratory viruses, the outcomes may not be as severe. So, is it really that much more transmissible? I think that’s an outdated concept. But certainly, just like for any of the other viruses, if you have a susceptible population, you will have trouble. Context is more important when discussing how transmissible a virus is.
How do you treat measles?
The vaccine is preventative care. There’s no real treatment other than the usual suspects: Staying hydrated, getting plenty of rest and using emollients for the rash to cut down on itching. There aren’t really any antiviral treatments.
Do people have lasting immunity to measles?
Our immunity to RNA viruses, like measles virus, tends to be shorter-lived than we previously thought. If you’re over 50, it’s a very good idea to have your titer checked, which means reevaluating your antibody level for measles. What we should also do is pay attention to both arms of the immune system: The B cell response, or the antibody response, and the T cell response. T cells kill off virus-infected cells, so for viral infections, those are really important.
Who is most at risk of measles or having serious complications?
Most older Americans probably already have some type of immunity to measles, either naturally acquired or through vaccines. It’s the young ones who haven’t been vaccinated that are at risk. When we talk about measles infections, we mean those capable of transmitting the virus up to four days before symptoms display and four days after symptoms have dissipated. Just because you’re not “sick,” doesn’t mean you aren’t infectious.
Pregnant people should also be cautious because a transient depression of the immune system occurs when you’re pregnant. Communities that are somewhat isolated with a high number of non-vaccinated people are also at risk for developing measles-related complications. Specifically, these are people who, for the most part, may not adhere to standard vaccine recommendations. It’s not just true for measles; it’s true for other preventable diseases as well.
How do you prevent measles?
Staying away from sick people, of course. If someone’s sick and you don’t have to be near them, don’t be near them.
It is a good idea to stay home with a child that has been exposed to measles or has an active measles infection. Going to work is not recommended. If you must, you should inform your coworkers about the situation. I also think it’s a good idea to specifically stay away from people with little kids that may have measles.
Overall, the best thing to do if you’re sick is to self-isolate, and I’ll be the first to say N95 masks are great for this sort of thing to reduce the chances of transmitting the virus to others that come into contact with you.
Written by: Sydney Burge