By Neha Mukherjee and Deidre McPhillips, CNN

(CNN) — Twenty-three measles cases have been reported in Kansas, and the state health department said they could be linked to an ongoing outbreak that has infected at least 379 people across Texas, New Mexico and Oklahoma.

“The confirmed cases in Kansas have a possible link to the outbreaks in Texas and New Mexico. While genetic sequencing of the first Kansas case reported is consistent with an epidemiological link to the Texas and New Mexico outbreaks, the source of exposure is still unknown,” Jill Bronaugh, communications director for the Kansas Department of Health and Environment, said in an email Wednesday.

Children account for 21 of the Kansas cases, and 20 of the cases are in people who are unvaccinated.

The Kansas measles cases are concentrated in the southwestern part of the state and have spread to six counties.

Most of the public school districts in these counties have vaccination rates that are well below the recommended 95% threshold set by the Department of Health and Human Services to stop spread of the virus. Hugoton Public Schools in Stevens County, which accounts for more than a quarter of the cases, had an 83% vaccination rate among kindergartners last school year, according to data from the state health department. And the Sublette Unified School District in Haskell County had a vaccination rate of just 44%.

Statewide, 90.4% of incoming kindergartners in the 2023-24 school year had received the measles-mumps-rubella (MMR) vaccine, US Centers for Disease Control and Prevention data shows. Only 15 other states had lower coverage rates.

Religious exemptions for vaccinations have risen in Kansas over the past decade. Last week, the state House of Representatives passed a bill including language that would expand such exemptions. The measure, which also aims to increase child care availability and capacity, is now being debated in a state Senate committee.

“The provision in HB2294 is simply bad public health policy and Kansas children will be harmed by it,” Dr. Brandon Kennedy, chair of the Immunize Kansas Coalition, said in a statement last week.

As part of the wider measles outbreak, Texas has reported 327 cases as of Tuesday, and New Mexico reported 43 cases. Oklahoma has reported nine cases: seven confirmed and two probable.

Forty-two people have been hospitalized and one death reported, a school-age child who was not vaccinated and had no underlying conditions. Health officials in New Mexico are also investigating the cause of death of an unvaccinated person who tested positive for measles.

Most of the cases in Texas are in Gaines County, where the outbreak was first identified. In New Mexico, most are in Lea County, which borders Gaines County.

Officials say the virus’ spread into additional counties is a problem.

“We’re continuing to see more counties with one case popping up. … It’s concerning every time we add additional counties with cases,” said Katherine Wells, director of Lubbock Public Health in Texas. “It indicates that people are either traveling through Gaines County and picking it up, or we’re having people infected with measles traveling outside the county.”

Tuesday’s update from the Oklahoma State Department of Health indicates links with the Texas and New Mexico cases.

“All cases are linked through exposures to household or extended family; and initial cases reported exposure to the measles outbreak in West Texas and New Mexico. At this time, no cases have resulted from exposure to public settings,” the agency said.

Although most of the cases in the outbreak have been in people who were unvaccinated or who had unknown vaccination status, six were found in people who said they have received at least one dose of MMR: two in Texas and four in New Mexico.

New Mexico’s case update Tuesday reported only one additional case since Friday, but local officials said they worry that the numbers will continue to grow.

“This is not necessarily a downward trend. It could just be a lull in what is an ongoing outbreak,” said Robert Nott, communications director for the New Mexico Department of Health. “We are not taking it for granted.”

The CDC is on the ground in Texas to help with infection control, including figuring out how to reduce exposures in patient waiting rooms and answering technical questions for health care providers who have never seen measles before, Wells said.

New Mexico has not requested CDC assistance, but the agency has been in communication with the health department, according to local officials.

There have been more than 400 measles cases reported in 20 states this year, according to CNN’s tally.

Less than a quarter of the way through 2025, this is already more than all of the cases reported last year. In 2024, there were 285 measles cases reported in the US, according to data from the US Centers for Disease Control and Prevention.

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