The number of measles cases in the United States has exceeded the previous record high for all of 2025, with five months remaining until 2026.
The U.S. Centers for Disease Control and Prevention recorded 2,318 measles cases as of Thursday, according to the agency’s update on Friday.
The number of measles infections in Japan in 2025 was 2,289, making it the worst year for measles outbreaks in more than 30 years. 2026 is certain to be the worst year for measles in the United States since 1991, with major outbreaks affecting hundreds of people in South Carolina, Utah, and Arizona, and smaller outbreaks in other states.
Global health officials are scheduled to meet in November to determine whether the United States and Mexico have lost measles-free status. The United States eliminated local measles outbreaks in 2000 by maintaining high vaccination rates, but in recent years vaccination rates have fallen below the 95% needed to prevent outbreaks.
The number of measles cases is underestimated
Measles cases are increasing in the United States, but it may be impossible to say exactly how widespread the spread is. Public health agencies and disease researchers have long acknowledged that official counts are incomplete because some people get sick and go untreated, which is not unique to measles.
The United States has the highest number of measles infections in a single year since measles was declared eradicated.
Additionally, experts say the virus is one of the most contagious known to medicine, and the spread may be greater than known because vaccination rates are declining nationwide. National immunization coverage against measles, mumps, and rubella has fallen from 95.2% in the 2019-20 school year to 92.5% of kindergarteners in the 2024-25 school year, but even lower coverage is obscured in certain regions.
Public health officials have been battling measles in Utah for more than a year, during which time the virus has sickened more than 700 people, according to the state health department. State epidemiologist Dr. Leesha Nolen said experts relying on mathematical modeling and genetic analysis suggest the size of the outbreak at the Utah-Arizona border could be about three to four times the size currently known.
The situation is even murkier in South Carolina, which has experienced the nation’s largest outbreak in 35 years. The state health department said the 997 total was likely an undercount, but it was unclear by how much.
Dr. Brannon Traxler, acting director of the state health department, said undercounts are “impossible to know and can fluctuate over the course of an outbreak.”
Gaps in data can make it difficult to reliably estimate the true extent of the outbreak. Experts say hospitalization rates can be a good barometer, but not all states require reporting of measles hospitalizations.
“If we really had some kind of hard standard for hospitalizations as a percentage of total cases and a measure of severity, that would give us another way to estimate the size of an outbreak and see if it’s consistent with other methods,” said Damon Toth, an applied mathematician at the University of Utah School of Medicine who is working on one of Utah’s outbreak analyses.
Researchers are still analyzing the 2025 Texas outbreak
In Texas, researchers are working to estimate the size of the state’s outbreak in 2025, with early findings showing it may have been nearly twice as large as the 762 known cases.
Remy Pasco, a mathematical epidemiologist at the University of Colorado Boulder who worked on the analysis, said the undercount was not surprising. Without adequate vaccination coverage in the region (95%, according to health experts), “once you get measles, there’s very little you can do about it,” he says.
The CDC defines an outbreak as three or more related cases. But by the time three such cases are confirmed in an area with low vaccination rates and poor disease surveillance, “we’ve either missed the previous cases or we’re going to have more cases,” he added.
Dr. Varun Shetty, Texas’ chief epidemiologist, said some people tested positive for measles, but health officials were unable to confirm who else was in the person’s household or whether they were sick.
Measles is back. My sister Marcy isn’t like that.
“What we can count and report almost always underestimates what is actually happening because it relies on people being willing to get tested and sharing information with health care providers and public health,” Shetty said. “Sometimes that just doesn’t happen.”
The state health department previously reported that 182 probable measles cases among minors in Gaines County, the epicenter of the outbreak, were unconfirmed in March 2025 due to lack of information. Overall, there have been 414 confirmed cases in West Texas counties during the outbreak.
Shetty expects there will be more measles cases and even outbreaks because so many people are unprotected.
“High vaccination rates are extremely important, not only for individuals but also for communities,” he said.
Doctor says vaccination is about protecting others
Dr. Mark Roberts, former director of the Public Health Dynamics Laboratory at the University of Pittsburgh School of Public Health, is most concerned about what he calls “innocent bystanders.”
Research and measles modeling by his team shows that those who cannot be vaccinated – young babies, people with weak immune systems, and those who rarely receive strong immunity from vaccines – bear the brunt of the outbreak early on.
Roberts said some people think skipping the vaccine is the same as deciding not to wear a seatbelt in a car.
“Not vaccinating your child is like saying, ‘I don’t want brakes on my car,'” he says. “Because it’s someone else who gets hit. You’re not the only one in the car. It’s other people, too.”
—Devi Shastri
