Public health officials in New Mexico have said they suspect some of the state's cases are linked to the Texas outbreak, but haven't confirmed it.
The Texas Department of State Health Services said Monday that 13 people are in hospital with measles.
State health officials say this outbreak is Texas' largest in nearly 30 years.
Health department spokeswoman Lara Anton said last week that cases have been concentrated in a "close-knit, under-vaccinated" Mennonite community — especially among families who attend small private religious schools or are homeschooled.
At least three of the New Mexico cases are in Lea County, which borders Gaines County in Texas.
The state health department has said people may have been exposed at a grocery store, a primary school, a church, Nor-Lea Hospital and a Walgreens in Hobbs, New Mexico.
Measles is a respiratory virus that can survive in the air for up to two hours.
Up to nine out of 10 people who are susceptible will get the virus if exposed, according to the US Centres for Disease Control and Prevention.
Most kids will recover from measles if they get it, but infection can lead to dangerous complications like pneumonia, blindness, brain swelling and death.
The measles, mumps and rubella vaccine is safe and highly effective in preventing measles infection and severe cases of the disease.
The first shot is recommended for children between 12 and 15 months old and the second between four and six years old.
The vaccine series is required for kids before entering kindergarten in US public schools.
Before the vaccine was introduced in 1963, the US saw some three million to four million cases per year.
Now, it's usually fewer than 200 in a normal year.
There is no link between the vaccine and autism, despite a now-discredited study and health disinformation.
In communities with high vaccination rates — above 95 per cent — diseases like measles have a harder time spreading through communities. This is called "herd immunity."
But childhood vaccination rates have declined nationwide since the pandemic and more parents are claiming religious or personal conscience waivers to exempt their kids from required shots.
The US saw a rise in measles cases in 2024, including an outbreak in Chicago that sickened more than 60.
Gaines County has one of the highest rates in Texas of school-aged children who opt out of at least one required vaccine, with nearly 14 per cent of K-12 children in the 2023-24 school year.
Health officials say that number is likely higher because it doesn't include many children who are homeschooled and whose data would not be reported.
Health workers are hosting regular vaccination clinics and screening efforts in Texas.
They are also working with schools to educate people about the importance of vaccination and offering shots.
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