As of March 6, 2025, there are active measles outbreaks in Texas, New Mexico and New Jersey. The largest of these, in Texas, includes 198 measles cases and the first measles death in the U.S. since 2015. The death occurred in an unvaccinated school age child. Most of the U.S. measles cases in 2025 have been among children ages 5-19 years (45% of cases) and children under 5 years (34% of cases). Nearly all measles cases (94%) have occurred in people who are unvaccinated or have unknown vaccination status. In 2025 to date, there have been more than twice as many measles cases in the U.S. as the same date in 2024.

Measles is one of the world’s most infectious diseases, and spreads through the air. The virus can remain active on surfaces and in the air for up to two hours. One person infected by measles can infect nine out of ten unvaccinated people they come into contact with.

Measles used to result in 48,000 hospitalizations each year before the vaccine was developed.

In the US, the vaccine is not given to babies under 1 year of age or people with weakened immune systems. This makes these groups especially susceptible to infection if they are exposed to someone with the virus. As a result, they can only rely on herd immunity (having around 95% of the population immunized) to help protect them against measles.

Side effects of the measles vaccine have been well researched. About 10% of children will develop a fever 6-12 days after vaccination, and some experience a small rash. In very rare cases, the fever can induce seizures.

Two doses of the vaccine (MMR vaccine) are 97% effective at preventing measles, and one dose is 93% effective. Breakthrough infections, especially somewhere where high levels of measles outbreaks are occurring, are possible. The MMR vaccine protects against measles, mumps, and rubella.

Multiple studies have shown no connection between the measles vaccine and autism. Autism symptoms begin to show in children around the same time a child is receiving vaccines. It makes sense to suspect vaccines as a cause, and research has looked into this for that reason. However, according to these studies, the timing is coincidental.

Parents can have conversations with their doctors to decide if their child should receive the measles vaccine, and choose a timeline that works best for their family.

The CDC and state health departments are actively monitoring measles outbreaks and measles cases. The CDC website is updated every Friday with updated measles information.