Quick Facts

• Utah reports 583 confirmed measles cases since the outbreak began in summer 2025, making it the nation’s largest active outbreak
• 83% of cases occur among unvaccinated people, with children outpacing adults by nearly 2-to-1
• Utah’s kindergarten vaccination rate of 88.6% falls below the 95% threshold needed for herd immunity

Utah’s measles outbreak has reached 583 confirmed cases since it began in summer 2025, making it the nation’s largest active outbreak. State officials recorded 24 new cases in the past five days, with the virus now spreading across every corner of the state.

The outbreak started in small communities along the Utah-Arizona border last summer. It has since spread statewide, with recent exposures at a high school wrestling tournament and the University of Utah campus accelerating transmission.

Dr. Leisha Nolen, Utah’s state epidemiologist, said the outbreak has evolved beyond specific communities. “It is now hitting people from all different areas of the state with all different practices, from all different kinds of communities,” Nolen said. “It isn’t limited to any specific group anymore.”

Of the 583 total cases, 83% occurred among unvaccinated individuals. Children represent nearly twice as many cases as adults. State officials report that 56 vaccinated people contracted measles during the outbreak, reflecting the virus’s high transmission rate when community immunity drops.

Utah’s kindergarten vaccination rate sits at 88.6%, below the national average of 92.5% and well under the 95% threshold needed for herd immunity. In Washington County, where the outbreak began, only 79.2% of kindergarteners received the MMR vaccine.

Health officials express concern about case severity. “It is not a mild infection. It is not a mild virus. It is severe illness,” Nolen said at a recent briefing. Many patients experience breathing difficulties, dehydration, and high fevers.

Measles poses the greatest danger to children under 5 and people with compromised immune systems. Severe complications can include pneumonia, brain swelling, and death. Three measles deaths were recorded nationally in 2025.

The outbreak has prompted a 31% increase in MMR vaccine administration statewide compared to the same period last year. However, Nolen said this increase remains insufficient to stop transmission.

Utah now accounts for nearly half of the nation’s new measles cases each week. As of April 2, 2026, the United States reported 1,671 confirmed measles cases nationwide, with 94% linked to outbreaks.

“There’s still a larger number of people out there who haven’t been vaccinated against the measles virus and are at risk of getting this pretty bad infection,” Nolen said. With widespread community transmission established, officials acknowledge the challenge of containment.

Read more: A measles outbreak that began in rural Utah continues to spread