Measles outbreak: how contagious is it and what are the symptoms?

The Guardian

28-02-2025

Twenty-five years ago, the US eliminated the measles virus. Measles is extremely contagious, and sporadic cases and outbreaks are expected.
But as of 28 February, 146 people in Texas – the majority of whom are unvaccinated children – have contracted measles. Twenty have been hospitalized, according to the Texas department of state health services. One 'school-aged child' who was not vaccinated died this week, according to a 26 February statement – the first measles death in the US since 2015.
Nine other cases have been reported in a neighboring county in New Mexico, say state health officials.
'This is a significantly sized outbreak,' says Dr Adam Ratner, a pediatric infectious disease physician in New York City and author of the book Booster Shots: The Urgent Lessons of Measles and the Uncertain Future of Children's Health. The CDC defines an outbreak as three or more related cases; last year, a total of 285 cases were reported across 31 states and Washington DC.
Here's everything to know about measles as the virus spreads.
The last major US measles outbreak occurred in 2019, when nearly 1,300 people caught the virus. According to the CDC, this almost cost the US its elimination status. (Measles is considered eliminated when it hasn't spread in a region for 12 or more consecutive months.)
Dr Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston, says the latest case numbers are 'still the tip of the iceberg' and are on track to reach or surpass those of past outbreaks.
That's largely due to declines in vaccination rates in the US and worldwide that have contributed to a fourfold rise in measles outbreaks from 2023 to 2024 alone. 'I think we're still on that trajectory,' Hotez says. 'I would imagine 2025 is going to be a pretty rough year for measles.'
Measles is a respiratory virus that mostly affects children, but can also affect adults who were never infected or vaccinated against it, says Robert Bednarczyck, an epidemiologist and associate professor of global health at Emory University in Georgia.
Measles is often lumped together with mumps and rubella because there's one vaccine, known as MMR, that protects against all three diseases. But they're each caused by different respiratory viruses.
The measles virus lives in the nose and throat mucus of infected people. When they cough, sneeze or breathe, viral particles slingshot into the air, where they can linger for up to two hours. 'You don't even have to have direct or close contact with an infected individual' to get sick, says Hotez. This is why measles is one of the most contagious viruses we know of.
According to the CDC, if one person has measles, up to 90% of people who are not immune and breathe the contaminated air or touch an infected surface will get sick. Unlike other respiratory bugs, it is not seasonal.
A person infected with measles is contagious for about eight days, including the four days before a rash appears, and the four days after. This is problematic, says Ratner, because it means you can spread the virus without knowing it.
You may not know you have measles right away because symptoms typically emerge one to two weeks after exposure. Around that time, you might develop a cough, runny nose, red and watery eyes, and high fever, according to the CDC. At this point you might assume you have the flu, but in another two to three days you may find tiny white spots inside your mouth, Bednarczyck says, which 'is a clear giveaway' for measles.
Three to five days in, you might develop the classic rash: red patches on the face that dot the hairline, then spread to the neck, trunk, arms, legs and feet, says the CDC. The darker your skin, the more likely you'll see small raised bumps in the same areas without discoloration. Although it looks painful, a measles rash usually isn't itchy.
Overall, you might feel sick for about a week, says the World Health Organization, and the rash could take five to six days to fade away. If you suspect that you or your child has measles, call the doctor's office or hospital before you arrive, says Ratner, so they can reduce your exposure to others in the waiting room.
Most people who catch measles recover with no lingering consequences, say experts. But complications can affect a relatively large number of people who get the virus; some are very serious.
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Ear infections, for example, occur in about one out of every 10 children with measles, according to the CDC. As many as one in 20 will get pneumonia, which is the most common cause of measles-related death in young kids. About one in every 1,000 children will develop brain swelling called encephalitis, which can cause deafness, convulsions or intellectual disability. Data show that about one to three of every 1,000 kids with measles will die from these complications.
A fatal central nervous system disease called subacute sclerosing panencephalitis can happen to very few people about seven to 10 years after they recover from measles; the risk is higher for those who get measles before age two.
Unvaccinated people, children younger than age five, adults over age 20, people with weakened immune systems, and pregnant people face the greatest risks of measles complications, says the CDC. Even so, it's important to remember that anyone, regardless of their health, can get seriously ill and die from measles, says Ratner – especially considering there are no treatments for the virus. Some hospitalized people may receive vitamin A, which may reduce their risks of bad outcomes, says Ratner, but it's not a cure.
Because measles is airborne, face masks can help protect against infection, experts say. But vaccination is by far the best way. Before the US measles vaccination program began in 1963, about 3 to 4 million people caught the virus, 48,000 were hospitalized, 1,000 developed encephalitis, and 400 to 500 died each year in the US, according to CDC data.
There are two doses. The first, which children get aged 12 to 15 months, is about 93% effective, and the second, which kids get between ages four and six, is about 97% effective. That means roughly three out of every 100 people who are fully vaccinated still get measles after exposure to the virus, says the CDC.
Still, the vaccine can lower the odds of severe disease and the likelihood of spreading it to others, says Ratner, including those who can't get vaccinated because they're too young or have weakened immune systems. And research suggests that the virus diminishes the antibodies you've acquired for other germs, says Bednarczyck, leaving you vulnerable to all sorts of infections, especially if you aren't vaccinated.
The measles shot is safe, according to decades of research. One infamous 1998 study of 12 children suggested a link between MMR and autism; it was later retracted for 'scientific fraud'. Several papers have since proved that association wrong.
If you are exposed to measles and have not been vaccinated or have only received one dose, you can receive a measles vaccine within 72 hours of exposure, says Ratner, which could prevent infection or reduce the chances you get really sick. Kids too young for vaccination and people considered high-risk for severe disease could receive an antibody treatment called immunoglobulin within six days of exposure via IV or a shot in their arm.
Infection and vaccination against measles are both thought to offer lifelong immunity – that is, you can't get measles twice. But if you're unvaccinated and have been infected, says Ratner, you should roll up your sleeve anyway to protect against mumps and rubella.
MMR contains a weakened version of the measles virus, which causes a harmless infection that helps people develop immunity. So some people shouldn't get the vaccine, says the CDC, including those who are pregnant, have a weakened immune system due to disease or treatment, or have a parent or sibling with a history of immune system problems.
If you've been vaccinated, you don't have much to worry about. But overall, the CDC says measles is a concern for the US. Fewer children worldwide are getting their measles shots, fueled in part by Covid-related anti-vaccine rhetoric. This means infections could become more common as unvaccinated travelers spread the virus. 'Our control of measles is really a testament to the vaccine and our ability to use it,' says Bednarczyck, 'but we're potentially sitting right on the edge of where we might start seeing more widespread outbreaks.'
From the 2019-20 to 2023-24 school year, vaccinations among US kindergartners dropped from 95% to just below 93%. It's a concerning trend, says Ratner, because we need at least 95% vaccination coverage to achieve herd immunity, which is when enough people are immune to measles to prevent significant spread. Within individual states, rates can be even lower; Idaho, for example, has a 80% vaccination rate.