The measles case count in the United States for 2026 has already exceeded the total cases recorded in the record-breaking year of 2025, with still five months remaining in 2026.
According to an update from the U.S. Centers for Disease Control and Prevention (CDC) on Friday, there have been 2,318 measles cases reported as of Thursday.
In 2025, the U.S. experienced 2,289 measles cases, marking that year as the most severe in over three decades. However, 2026 has now become the worst year for measles since 1991, with significant outbreaks in South Carolina, Utah, and Arizona affecting hundreds, and smaller clusters emerging in other states.
In November, international health officials are set to convene to assess whether the U.S. and Mexico have lost their measles-free status. The U.S. had achieved the elimination of local measles spread in 2000 through high vaccination rates, which have since decreased to below the 95% threshold needed to prevent outbreaks.
Measles cases are undercounted
Although measles cases in the U.S. are increasing, determining the full extent of the spread remains challenging. Public health departments and disease researchers acknowledge that official counts are often incomplete, as some individuals may become ill and not seek treatment — a situation not unique to measles.
Experts suggest the actual spread might be more extensive than reported due to the virus’s high contagion level and declining vaccination rates across the country. National vaccination rates for measles, mumps, and rubella have decreased to 92.5% among kindergartners in the 2024-25 school year from 95.2% in 2019-20, with even lower rates in specific communities.
In Utah, where health officials have battled measles for over a year, more than 700 people have contracted the virus, according to the state health department. Mathematical modeling and genetic analyses suggest an outbreak on the Utah-Arizona border could be three to four times larger than currently recorded, as stated by state epidemiologist Dr. Leisha Nolen.
In South Carolina, which faced the largest outbreak in 35 years, the reported total of 997 cases is likely an undercount, the state health department indicated, though the extent of the undercount is unknown.
Dr. Brannon Traxler, acting director of the state department of health, noted that the undercount is “impossible to know and may vary during the course of an outbreak.”
Gaps in data make estimating an outbreak’s true scope difficult. Experts point out that while hospitalization rates can serve as a good indicator, measles hospitalizations are not required to be reported in every state.
“If we really had some kind of solid gold standard for the percentage of all cases that have hospitalization or some measure of severity, then that would be another way of estimating the outbreak size that we could see if it’s consistent with these other methods,” said Damon Toth, an applied mathematician at the University of Utah’s medical school involved in one of the Utah outbreak analyses.
Researchers are still analyzing the 2025 Texas outbreak
In Texas, researchers continue to evaluate the state’s 2025 outbreak, with early findings suggesting it may have been nearly double the size of the 762 known cases.
Rémy Pasco, a mathematical epidemiologist at the University of Colorado Boulder, working on the analysis, remarked that the undercounts are unsurprising. Without an adequate community vaccination rate — 95% as advised by health experts — “there’s just not much you can do about measles once you have it,” he stated.
The CDC considers an outbreak to be three or more linked cases. In communities with low vaccination rates and limited disease surveillance, once three cases are identified, “either you missed the previous ones or you’re going to have a lot more,” Pasco added.
Dr. Varun Shetty, Texas’ chief state epidemiologist, mentioned that there were cases where individuals tested positive for measles, but health officials were unable to determine who else in the household might have been exposed.
“What we’re able to count and report is almost always an underestimate of what actually occurred, because it relies on people being willing to be able to get tested, to share information with healthcare providers and with public health,” Shetty explained. “Sometimes that just doesn’t happen.”
The state health department had previously reported that 182 probable measles cases went unconfirmed in March 2025 among minors in Gaines County — the outbreak’s epicenter — due to a lack of information. The confirmed case count for the entire outbreak in western Texas County is 414.
Shetty anticipates continued measles cases and potential outbreaks because many individuals remain unprotected.
“It’s really critical, not only for individual people, but for communities, to have high vaccination coverage,” he emphasized.
Vaccination is about protecting others, physician says
Dr. Mark Roberts, retired director of the Public Health Dynamics Lab at the University of Pittsburgh School of Public Health, expresses concern for those he refers to as “innocent bystanders.”
Research and measles modeling by his team reveal that individuals who cannot receive vaccinations — such as young infants, immunocompromised individuals, and those who seldom acquire robust immunity from the vaccine — are disproportionately affected during outbreaks.
Roberts points out that some view skipping vaccination as comparable to choosing not to wear a seatbelt in a car.
“Not vaccinating your kid is like saying, ‘I don’t want my car to have brakes,'” he remarked. “Because it’s other people that you can hit. It’s not just you in your car. It’s other people.”
— Devi Shastri
