On Apr. 17, 2025, the Department of Public Health and Human Services (DPHHS) and the Gallatin City-County Health Department (GCCHD) reported Montana’s first cases of measles since 1990. 

The GCCHD investigated five confirmed cases of measles. The individuals were children and adults who were exposed to measles while traveling outside of Montana. The cases reside in Gallatin County and are currently isolated at home. All five individuals are unvaccinated, or vaccine status is unknown.

The GCCHD continues to assess any potential exposures while the individuals were contagious and are contacting the people who may have been exposed. People potentially exposed were provided with information about the exposure date and disease symptoms to watch out for.

The GCCHD determined that there were points of exposure to the general public. Potential exposures to the public can be found on the GCCHD website and were updated as needed or as more information became available. The spread of measles can occur before people know they have the disease, and before any rash appears.

Individuals who are immune to measles through vaccination, laboratory evidence of immunity, laboratory confirmation of disease, or were born before 1957 are not considered at risk for infection. Individuals without prior measles infection or vaccination have a 90% likelihood of contracting the disease if exposed.