The United States has already recorded more measles cases this year than in all of 2025, marking the highest tally since 1991. As of Friday, the U.S. Centers for Disease Control and Prevention reported 2,318 cases, surpassing the previous year's total of 2,289. This surge has made 2026 the worst year for measles in the U.S. in over three decades, fueled by significant outbreaks in South Carolina, Utah, and Arizona, and smaller clusters in other states.
International health officials are set to meet in November to assess whether the U.S. and Mexico have maintained their measles-free status. The U.S. had previously eliminated local measles transmission in 2000 by maintaining high vaccination rates, but these have declined in recent years to below the 95% coverage recommended by experts for outbreak prevention.
National vaccination rates for measles, mumps, and rubella dropped to 92.5% among kindergartners in the 2024-25 school year, down from 95.2% in 2019-20. These national figures can mask even lower vaccination rates within specific communities.
Experts believe that official case counts may be an undercount. Some individuals may experience mild symptoms and not seek medical treatment, or their cases may not be officially reported. Measles is highly contagious, and public health officials acknowledge that the true extent of its spread is difficult to ascertain.
In Utah, where health officials have been addressing measles for over a year, more than 700 people have fallen ill. State epidemiologist Dr. Leisha Nolen indicated that mathematical modeling and genetic analyses suggest a large outbreak on the Utah-Arizona border might be three to four times larger than currently documented.
South Carolina, which experienced its largest outbreak in 35 years, reported 997 cases. The state health department indicated this number is likely an undercount, though the extent remains unknown. Dr. Brannon Traxler, acting director of the state department of health, noted that estimating the precise number of undercounted cases is impossible and can fluctuate during an outbreak.
Data gaps, such as the lack of mandatory state-level reporting for measles hospitalizations, complicate efforts to accurately gauge outbreak severity. Damon Toth, an applied mathematician at the University of Utah, suggested that hospitalization rates could serve as a barometer if data were consistently collected and reported nationwide.
Researchers are still analyzing the 2025 outbreak in Texas, with early findings suggesting it may have been nearly twice the reported 762 cases. Rémy Pasco, a mathematical epidemiologist at the University of Colorado Boulder, stated that undercounts are unsurprising in areas with inadequate vaccination coverage, where measles can spread rapidly once introduced.
Dr. Varun Shetty, Texas' chief state epidemiologist, highlighted instances where positive measles tests could not be fully investigated due to incomplete information about household contacts or other sick individuals. He emphasized that reported figures are almost always an underestimate because they rely on individuals seeking testing and sharing information with health authorities.
Physicians like Dr. Mark Roberts, retired director of the Public Health Dynamics Lab at the University of Pittsburgh, express concern for vulnerable populations, including infants, those with compromised immune systems, and individuals who do not develop robust immunity from the vaccine. He likened the decision not to vaccinate to foregoing essential safety measures, emphasizing that vaccination protects not only the individual but also the broader community.