What Is Measles? The Highly Contagious Respiratory Infection Explained
Key takeaways:
Measles (rubeola) is a very contagious viral illness that can cause serious health complications.
Measles outbreaks still happen in the U.S. because fewer people are getting vaccinated against the illness.
Measles can be prevented with a vaccine that’s safe, effective, and doesn’t cause autism.
Table of contents
Measles is a viral illness that mostly affects young children. In many parts of the world, measles is still a major cause of illness and even death. Thanks to the measles vaccine, which was introduced in the 1960s, the U.S. is largely free of measles. But outbreaks are on the rise.
How did measles elimination — one of the biggest public health success stories in U.S. history — almost turn into one of the biggest failures? Let’s take a closer look at measles.
How does measles spread?
Measles, also called rubeola, is an illness caused by the virus paramyxovirus. Paramyxovirus is a respiratory virus, which means it’s spread through respiratory droplets, just like influenza or COVID-19.
A person with measles releases the virus anytime they talk, cough, or sneeze. The virus particles can then travel through the air and infect other people who are nearby and happen to breathe in those droplets. This is called airborne transmission.
Measles can also spread through surfaces, but this is less common. When someone coughs or sneezes and then touches an object, they can transfer the virus onto that object. When another person touches these objects and then touches their face, they can pick up the virus and get sick.
Is measles contagious?
Yes, measles is one of the most contagious diseases in human history. Measles is so contagious that if someone who isn’t immune comes in contact with the virus, they have a 90% chance of getting sick.
Do you need a measles booster? Our experts review who should get another measles vaccine.
Measles prevention: Measles is extremely contagious. Here are our top tips for prevention.
Not sure what’s causing your child’s rash? Our image guide to the most common rashes in kids can help.
Like with COVID-19, people with measles don’t have symptoms right away. That means they can pass it to other people because they don’t realize they are sick.
Research shows that each person with measles passes the virus to up to 18 other people. In comparison, someone with COVID-19 passes the virus to five or six other people.
What are the symptoms of measles?
When someone gets measles, they develop symptoms similar to other respiratory viral diseases, such as:
High fever
Cough
Congestion or runny nose
Conjunctivitis (pink eye)
These symptoms usually start between 1 and 2 weeks after someone comes in contact with the virus.
A few days after these symptoms start, people develop the classic measles rash. The rash starts off as flat, red spots near the hairline. It spreads down the body to the feet over several days. The spots may join together as they spread.
People may also develop white spots in the back of their throat called Koplik spots.
There’s no treatment for measles, so people have to recover on their own. Some people experience only mild symptoms, but many develop more serious complications while they are sick. Some people also develop lifelong medical problems because of measles.
What does measles look like?
Here’s what the classic measles symptoms, including the measles rash, can look like.
Measles complications are common
A rash, fever, and cough may not sound like a serious illness. But the problem with measles is that it can cause serious complications. And these complications are very common, especially in:
Children younger than 5 years
Adults older than 20 years, even if they have no health issues
Pregnant women
Those with a weakened immune system
Complications happen more frequently from measles than other viruses. Here are some facts about complications from measles:
Among people with measles, 1 out of 5 needs to be hospitalized.
Among children with measles, 1 out of every 10 gets pneumonia.
Among children with measles, 1 out of every 1,000 gets brain swelling that can lead to permanent intellectual disability, lifelong seizures, and hearing loss.
Among children with measles, about 2 out of every 1,000 will die.
The complication and death rates are a major reason for the ongoing, worldwide vaccine campaign. Another reason is that measles is extremely dangerous.
Are there still measles outbreaks in the U.S.?
Measles has been eliminated in many countries, including the U.S. But this doesn’t mean that the disease never occurs in the U.S. — it just means that the virus isn’t endemic.
Viruses like influenza are endemic. That means that every year we can expect a flu season because the virus is always around. Once a virus isn’t endemic anymore, the only way people can get the virus is if it’s brought into an area from somewhere else.
In most of the outbreaks, an unvaccinated person from the U.S. traveled outside the country and came back with measles. Because measles is so contagious, these people rapidly passed measles to all the unvaccinated people in their local community.
Until measles is eliminated from every country, unvaccinated people will continue to get measles and bring it into the U.S. This is a problem for two reasons:
More people are traveling internationally than ever before.
Fewer people are getting vaccinated against measles in the U.S.
Because measles is so contagious, 95% or more of a population needs to be vaccinated against measles to stop an outbreak. But fewer and fewer states in the U.S. reach this 95% threshold. Research has shown that low immunization rates are the reason for ongoing measles outbreaks in the U.S.
How can you prevent the measles?
The most important thing you can do to protect yourself and your loved ones from measles is to get the measles vaccine. The measles vaccine is safe and effective, and doesn’t cause autism. The measles vaccine is given as a combination vaccine with mumps, rubella, and sometimes chicken pox.
Being fully immunized against measles will keep you safe both in the U.S. and while traveling in other countries.
What to do if you are exposed to the measles
Contact your local health department and your primary care provider if you think you were exposed to the measles. It’s important to report any possible exposures even if you are fully vaccinated.
The health department may ask you to isolate at home for several days. People who are unvaccinated will also be offered the measles vaccine or measles immunoglobulin. These treatments may help lower the risk of developing serious illness from measles.
Frequently asked questions
No, you cannot get measles twice. People who get measles will develop lifelong immunity to the virus. But they may still develop complications from measles later in life.
Measles can be deadly. In fact, about 2 out of every 1,000 children die from measles, even if they have no medical conditions. The risks are higher for children who have underlying medical conditions. Adults of all ages can also develop serious complications and die from measles. The risk is higher if you are pregnant or have a weakened immune system.
If you are pregnant, you are more likely to develop serious health complications from measles, such as pneumonia, severe illness, and death. Measles during pregnancy can also lead to premature birth and stillbirth.
The bottom line
Measles is one of the most contagious viral illnesses in the world. Children, adults, pregnant women, and those with weakened immune systems are most at risk for serious complications from measles. Outbreaks of measles are increasing because of low vaccination rates. The best way to protect yourself against measles is to get vaccinated against the virus.
Why trust our experts?
Images used with permission from VisualDx (www.visualdx.com).
References
Centers for Disease Control and Prevention. (2024). How measles spreads.
Centers for Disease Control and Prevention. (2024). Measles symptoms and complications.
Centers for Disease Control and Prevention. (2025). Measles cases and outbreaks.
Dimala, C. A., et al. (2021). Factors associated with measles resurgence in the United States in the post-elimination era. Scientific Reports.
Guerra, F. M., et al. (2017). The basic reproduction number (R 0) of measles: A systematic review. The Lancet. Infectious Diseases.
Macmillan, C. (2025). Measles cases are on the rise: What to know. Yale Medicine.
McLean, H. Q., et al. (2013). Prevention of measles, rubella, congenital rubella syndrome, and mumps, 2013: Summary recommendations of the advisory committee on immunization practices (ACIP). Morbidity and Mortality Weekly Report.
Phadke, V. K., et al. (2016). Association between vaccine refusal and vaccine-preventable diseases in the United States: A review of measles and pertussis. JAMA.
Sanche, S., et al. (2020). High contagiousness and rapid spread of severe acute respiratory syndrome coronavirus 2. Emerging Infectious Diseases.
U.S. Travel Association. (2025). Travel forecast.
Wang, C. C., et al. (2021). Airborne transmission of respiratory viruses. Science.
