Measles outbreak spreads to 9th state: What to know

Montana has become the ninth state to have an active measles outbreak in the U.S.

State health officials announced five cases last Thursday in unvaccinated children and adults who had traveled out of state. The cases were officially confirmed on Monday.

The five cases are being traced in Bozeman and Belgrade and are the state’s first measles cases in 35 years, health officials said. 

Measles outbreaks across US

Dig deeper:

There are currently measles outbreaks in Texas, Kansas, Oklahoma, Ohio, Indiana, Pennsylvania, Michigan and now Montana. 

In North America, an outbreak in Ontario, Canada has sickened 925 from mid-October through April 16. That's on top of cases in Mexico that the World Health Organization has said are linked to the Texas outbreak. A large outbreak in Chihuahua state has 433 cases as of April 18, according to data from the state health ministry.

Texas is driving the high numbers in the U.S., with an outbreak centered in West Texas that started nearly three months ago. Two unvaccinated elementary school-aged children died from measles-related illnesses near the epicenter in Texas, and an adult in New Mexico who was not vaccinated died of a measles-related illness.

By the numbers:

• Texas: 597 cases
• Kansas: 37 cases
• Oklahoma: 12 cases
• Ohio: 30 cases
• Indiana: 8 cases
• Pennsylvania: 9 cases
• Michigan: 7 cases

There have been 800 cases in 2025 as of Friday, according to the U.S. Centers for Disease Control and Prevention, and 10 clusters — defined as three or more related cases.

Measles cases have been reported in Alaska, Arkansas, California, Colorado, Florida, Georgia, Hawaii, Kentucky, Louisiana, Maryland, Minnesota, New Jersey, New York, Rhode Island, Tennessee, Vermont, and Washington.

What is measles?

Why you should care:

Measles is a highly contagious virus that can survive in the air for up to two hours.

Up to 9 out of 10 susceptible people will get the virus if exposed, according to the U.S. Centers for Disease Control and Prevention. Before the vaccine was introduced in 1963, the U.S. saw some 3 million to 4 million cases per year. Now, it’s usually fewer than 200 in a normal year.

It is preventable through vaccines and has been considered eliminated from the U.S. since 2000.

FILE - A health care worker fills a syringe with the MMR vaccine, at a vaccine clinic put on by Lubbock Public Health Department on March 1, 2025 in Lubbock, Texas. (Photo by Jan Sonnenmair/Getty Images)

Measles vaccine

What you can do:

The best way to avoid measles is to get the measles, mumps and rubella (MMR) vaccine. The first shot is recommended for children between 12 and 15 months old and the second between 4 and 6 years old.

Getting another MMR shot is harmless if there are concerns about waning immunity, the CDC says.

People who have documentation of receiving a live measles vaccine in the 1960s don’t need to be revaccinated, but people who were immunized before 1968 with an ineffective measles vaccine made from "killed" virus should be revaccinated with at least one dose, the agency said.

People who have documentation that they had measles are immune and those born before 1957 generally don’t need the shots because most children back then had measles and now have "presumptive immunity."

In communities with high vaccination rates — above 95% — diseases like measles have a harder time spreading through communities. This is called "herd immunity."