Montana is the ninth U.S. state to have an active measles outbreak.
The U.S. was up to 800 cases of measles nationwide on Friday. Texas is driving many of the numbers, with a small outbreak centered in West Texas that started nearly three months ago and is up to 597 cases. Two unvaccinated elementary school-aged children died from measles-related illnesses near the epicenter in Texas, and an adult in New Mexico later died of a measles-related illness.
Other states with active outbreaks — defined as three or more cases — include Indiana, Kansas, Michigan, Oklahoma, Ohio, Pennsylvania and New Mexico. The U.S. has more than double the number of measles cases it saw in all of 2024.
Measles is caused by a highly contagious virus that’s airborne and spreads easily when an infected person breathes, sneezes or coughs. It is preventable through vaccines, and has been considered eliminated from the U.S. since 2000.
Health experts fear the virus will take hold in other U.S. communities with low vaccination rates and that the spread could stretch on for a year.
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.
The Associated Press contributed to this report.