The New Mexico Department of Health said Thursday that the state had its first measles death.

A person in New Mexico tested positive for the measles virus after death, the state Health Department said. The official cause of death is still being investigated.

The adult, who was unvaccinated, didn’t seek medical care before dying, the Health Department said.

Measles is spreading rapidly in West Texas, with 159 cases as of Tuesday. Most of the cases are in Gaines County. In neighboring Lea County, New Mexico, 10 cases have been identified.

A school-age child in Texas last week was the first person to have died in the outbreak and the first to have died from measles in the United States in a decade.

Most of the people who have gotten the measles in Texas haven’t been vaccinated, including the child who died.

Experts say the most effective way to prevent measles is the MMR vaccine. Two doses are 97% effective.

On Sunday, Health and Human Services Secretary Robert F. Kennedy Jr. wrote in an editorial that “vaccines not only protect individual children from measles, but also contribute to community immunity.”

But Kennedy, a longtime anti-vaccine activist, stopped short of calling for parents to vaccinate their children. “The decision to vaccinate is a personal one,” he wrote.