Texas measles outbreak surpasses 600 cases with most among children, teens

The measles outbreak in western Texas has now reached 624 cases, with 27 new infections confirmed over the last five days.

Nearly all of the cases are among unvaccinated individuals or among those whose vaccination status is unknown, according to new data published by the Texas Department of State Health Services (DSHS) on Tuesday.

Currently, 10 cases are among residents who have been vaccinated with one dose of the measles, mumps and rubella (MMR) vaccine, while 12 cases are among those vaccinated with two doses.

At least 64 measles patients have been hospitalized so far, according to the DSHS. The majority of confirmed cases have presented in children and teenagers between ages 5 and 17, followed by children ages 4 and under.

Gaines County, which borders New Mexico, remains the epicenter of the outbreak, with 386 cases confirmed so far, DSHS data shows.

The increase in cases comes as five measles cases have been confirmed in Montana. The patients were exposed while traveling outside of Montana and are either unvaccinated or have unknown vaccination status, the state Department of Public Health & Human Services (DPHHS) said in a press release.

Montana DPHHS and the Gallatin City-County Health Department said that these are the first measles cases recorded in Montana in 35 years.

Three additional states – Louisiana, Missouri and Virginia – also reported their first measles cases of 2025 within the last week.

Additionally, two new measles cases have been confirmed in Indiana, connected to an earlier reported outbreak, bringing the total cases in the state to eight, according to the Indiana Department of Health.

As of Friday, the Centers for Disease Control and Prevention (CDC) has so far confirmed 800 measles cases in at least 24 states: Alaska, Arkansas, California, Colorado, Florida, Georgia, Hawaii, Indiana, Kansas, Kentucky, Maryland, Michigan, Minnesota, New Jersey, New Mexico, New York, Ohio, Oklahoma, Pennsylvania, Rhode Island, Tennessee, Texas, Vermont and Washington. That number is likely an undercount due to delays in states reporting cases to the federal health agency.

Among the nationwide cases confirmed by the CDC, about 97% are in people who are unvaccinated or whose vaccination status is unknown. Of those cases, 1% are among those who have received just one dose of the MMR inoculation and 2% are among those who received the required two doses, according to the CDC.

The CDC currently recommends that people receive two vaccine doses, the first at ages 12 to 15 months and the second between 4 and 6 years old. One dose is 93% effective and two doses are 97% effective against measles, the CDC says. Most vaccinated adults don't need a booster.

Public health officials may recommend a dose of the MMR vaccine as early as 6 months old for babies traveling internationally or in areas impacted by an outbreak in the U.S.

Measles was declared eliminated from the U.S. in 2000 due to the highly effective vaccination program, according to the CDC. However, CDC data shows vaccination rates have been lagging in recent years.

An outbreak lasting 12 months or more would threaten to end measles elimination status in the U.S. The large outbreak in Texas began in January of this year.

ABC News' Youri Benadjaoud and Jade Cobern contributed to this report.