Measles in the United States — March 2024

Summary

What CDC knows

Measles is an extremely contagious virus that can make people very sick. A measles infection can cause serious problems, like pneumonia, encephalitis (infection and swelling of the brain), or even death. The number of measles cases and outbreaks are rising globally, increasingly in countries often visited by U.S. travelers. Recently, measles outbreaks have been reported in multiple U.S. states, including in daycares and schools.

What CDC is doing

CDC works with state and local health departments to prevent the spread of measles. CDC recommends that everyone get the measles-mumps-rubella (MMR) vaccine. This vaccine is safe and works well to protect against these diseases. It is part of the routine immunization schedule for all children and adults that doctors follow. CDC also has special guidance for people travelling internationally. If measles cases are detected in a community, it is important for public health to take action to stop it from spreading. There's a well-known playbook to do just that. To prevent transmitting measles to others, people who are exposed to measles but haven't been vaccinated are recommended to stay home and away from settings where unvaccinated people may be exposed, like schools and daycares. This helps protect vulnerable people who are unable to get vaccinated from getting infected.

Measles in the United States

Thanks to a strong childhood vaccination program, measles was declared eliminated from the United States in 2000. Although overall childhood vaccination rates remain high in the U.S., measles still occurs frequently in other parts of the world. That’s especially true right now. The World Health Organization has noted a significant increase in measles cases worldwide, with a 30-fold increase in Europe. This includes popular international tourist destinations for Americans, like England.

Measles can easily come to the United States by way of unvaccinated travelers, and measles cases have been increasing around the country. This most commonly happens when people who live in the United States visit countries where there are measles outbreaks. Once someone gets measles and returns to America, measles can spread if people in their community aren't up-to-date on their vaccinations.

How measles spreads

• Measles is so contagious that if one person has it, up to 90% of the people close to them can also become infected if they are not protected by vaccination (or, less commonly, prior infection).
• The measles virus can stay in the air for up to 2 hours after an infected person left an indoor space.
• Someone can get infected by simply being in a room where a person with measles walked through.
• In addition, people with measles can transmit to others when their symptoms are fever, cough, and runny nose, which look like common respiratory viruses.

Common measles complications

Worse, measles can be very serious. Children younger than 5 years and adults older than 20 years are more likely to suffer from complications. Common measles complications include ear infections and diarrhea. More severe complications like pneumonia (lung infection) and encephalitis (infection and swelling of the brain) are possible and often require hospitalization and even intensive care. This is a real risk for people who are not vaccinated, especially for young children, adults, pregnant persons, and people who are immunocompromised.

On average, nearly 1 in 5 unvaccinated people in the United States who get measles need to be hospitalized. For example, in a recent outbreak in Ohio, over 40% of infants and children infected with measles were hospitalized.

When outbreaks do occur, local health departments lead the response. The playbook for ending measles outbreaks is decades old, and it works. People who are infected or who are exposed to measles but haven't been vaccinated are recommended to stay home and away from settings where unvaccinated people may be exposed, like schools and daycares. By following these simple procedures, countless jurisdictions have successfully curbed local measles outbreaks and limited the illness and suffering that accompany them.

Safe and effective MMR vaccination

Key to maintaining the elimination of measles in the U.S. is vaccination. The measles-mumps-rubella vaccine (MMR) is part of the national immunization schedule for all children and adults. Vaccination with MMR is the best and safest way to prevent measles. When both doses of MMR vaccine are given (typically when the child is about 1 and 4 years old), MMR is 97% effective at preventing measles.

CDC recommends the safe and effective MMR vaccination as part of the routine immunization schedule for all children and adults, with special guidance for those travelling internationally. With spring break travel coming up and people going to and coming from countries that have seen sharp upticks in measles cases, the time to be sure you and your family members are up to date on their MMR is now.