One of the largest measles outbreaks in the U.S. is now centered in bordering areas of southwestern Utah and Arizona.
In Southwest Utah, all but one of the 27 confirmed cases are among unvaccinated, school-age kids, the Southwest Utah Public Health Department reported. In Mohave County, Arizona, which health officials believe is connected to the Utah outbreak, there have been 42 confirmed cases of the highly contagious virus.
An NBC News investigation, done in collaboration with Stanford University, has found that much of the United States doesn’t have the vaccine protection to prevent outbreaks of communicable diseases such as measles.
About 79% of kindergartners in Washington County, Utah, are vaccinated against measles, according to NBC News data. That’s only slightly higher than rates in Gaines County, Texas, the epicenter of the 2025 outbreak earlier this year — and well below the 95% level of herd immunity experts say is needed to protect against an outbreak.
“I’ve worked for this health department for about 18 years, and we’ve never seen a case of measles that I know of up until this point,” said David Heaton, the public information officer for the Southwest Utah Public Health Department. “We are just at that low rate of (vaccine) uptake that does leave us open for this kind of an outbreak.”
Heaton said many community members were vaccine-hesitant before the pandemic, but Covid mandates made some people even more reluctant to get their shots.
“About a month ago, we started getting cases where we could see evidence of community spread, meaning that there was measles being passed on the ground in our five-county district,” said Heaton.
Cases have been steadily increasing in the district of more than 287,000 people and more are expected, health officials said.
The Mohave County Department of Public Health, which borders Utah, first announced a case on Aug. 12. Of the 42 confirmed cases, one child has been hospitalized.
In a statement, the Arizona Department of Health Services said that it’s working closely with officials in Mohave and Utah in a coordinated response to the ongoing outbreak. “This is the highest number of cases we have seen since the 1990s.”
The Arizona outbreak is primarily in Colorado City and the surrounding area, which is separated geographically from the rest of the state by the Grand Canyon. The rural area, which was founded in the 1930s and associated with fundamentalist Mormon leader Warren Jeffs, has a history of isolation.
“This is exactly what you expect to see when you have a highly infectious vaccine-preventable disease drop into a community with low vaccination rates, almost inevitable,” said Dr. Bob England, a former Arizona public health official affiliated with The Arizona Partnership for Immunization.
As of the 2024-25 school year, not a single school in Mohave County had kindergarten classes with herd immunity protection against measles.
According to data published by the Arizona health department, at Cottonwood Elementary School in Colorado City in Mohave County, the kindergarten rate for the measles-mumps-rubella (MMR) vaccine in 2024-25 was staggeringly low at 7.7%, with exemptions to the vaccine at 84.6%. Nearby, Masada Charter School reported a kindergarten MMR rate of 40%.
Arizona has lost about half a percent in immunization rates every year for more than a decade, England said. “What you see happening right now in the small, isolated communities could just as easily happen in any number of communities across our state and elsewhere where the immunization rate has fallen” England said. “That really adds up over time.”
Vaccination rates aren’t just declining in Arizona, but across the United States. Since 2019, 77% of counties and jurisdictions in the U.S. have reported notable declines in childhood vaccination rates. Among states that have data on the MMR vaccine, 67% of counties and jurisdictions now have immunization rates below 95%.
As MMR vaccination rates dwindle, the U.S. is experiencing the highest number of cases in more than 30 years. The Centers for Disease Control and Prevention has reported 1,514 cases and 40 outbreaks as of Sept. 23.
Last year there were 16 outbreaks.
The CDC is actively monitoring the measles spread in the close-knit communities along the Arizona-Utah border and ready to assist as needed, HHS Deputy Secretary and acting CDC Director, Jim O'Neill said in a statement Wednesday. "I encourage parents to vaccinate their children. Vaccines not only protect individual children from measles but also contribute to community immunity."
Officials in both Arizona and Utah are urging parents to get themselves and their kids up-to-date on the measles vaccine.
“It’s herd immunity that has protected us for decades from this disease, and it will continue to protect us if we don’t blow it,” said England.
Data from the NBC News investigation reveals that Mohave and Washington counties are in the middle of a cluster of counties with low MMR vaccination rates, creating concern of even further spread.
- Neighboring Yavapai County in Arizona is at 75.3%, while Navajo County is at 80%.
- Nearby, Kane, Iron and Piute counties in Utah all sit below herd immunity, with Iron and Kane just above 80% and Piute at 60%.
- Across the border in Nevada, Lincoln and Esmeralda counties are both below 70%, while Eureka County is at 75% and Nye County is at 82.5%.
Dr. Nathan Lo, infectious diseases physician and scientist at Stanford University School of Medicine, said the local nature of the outbreak underscores the importance of knowing vaccination rates at the county level.
“If you only have state-level data in Texas and Arizona, for example, vaccine coverage may seem relatively OK,” said Lo, the lead collaborator in the NBC News investigation.
Only with more detailed data at the county level is it possible to identify pockets that are very susceptible to surges in infections, he said. “Indeed, in the states like Texas and Arizona, that’s where the outbreaks have taken place.”
