The number of measles cases in the United States has already surpassed the total number of cases in 2025, with five months still remaining in 2026. According to the U.S. Centers for Disease Control and Prevention (CDC), there have been 2,318 cases reported as of Thursday. This surpasses the 2,289 cases documented in 2025, marking 2026 as the worst year for measles since 1991. South Carolina, Utah, and Arizona have experienced major outbreaks, while smaller clusters have appeared in other states.
Potential Loss of Measles-Free Status
International health officials are set to meet in November to assess whether the U.S. and Mexico will lose their measles-free status. The U.S. managed to eliminate local measles transmission in 2000 by maintaining high vaccination rates. Recently, these rates have dropped below the necessary 95% to prevent outbreaks.
Challenges in Tracking Measles Cases
Measuring the true spread of measles in the U.S. is challenging due to underreporting. Many people may get infected without seeking treatment. The virus is extremely contagious, exacerbating the spread in a context of declining national vaccination rates. In the 2024-25 school year, the vaccination rate for measles, mumps, and rubella fell to 92.5% among kindergartners, down from 95.2% in 2019-20.
In Utah, over 700 individuals have contracted measles, as reported by the state health department. Mathematical modeling suggests the outbreak near the Utah-Arizona border may be three to four times larger than reported, according to state epidemiologist Dr. Leisha Nolen.
Hospitalization as an Indicator
South Carolina experienced its largest measles outbreak in 35 years, with 997 reported cases. Dr. Brannon Traxler, acting director of the state health department, believes the true figure is higher but challenging to calculate precisely. Hospitalization rates can serve as an indicator of outbreak severity. However, not every state mandates reporting measles hospitalizations.
Damon Toth, an applied mathematician at the University of Utah, emphasizes the need for reliable hospitalization data to align outbreak estimates with other methods.
Undercounts in Texas
Texas researchers are still evaluating the 2025 outbreak, with preliminary results suggesting the outbreak was nearly twice as large as the known 762 cases. Remy Pasco, a mathematical epidemiologist, notes underreporting is common in areas lacking sufficient vaccination coverage.
Dr. Varun Shetty, Texas’ chief state epidemiologist, explains that undetected cases occur when individuals do not get tested or do not provide complete information. In Gaines County, 182 probable cases went unconfirmed due to lack of information, with the total confirmed cases being 414.
Importance of Vaccination
Dr. Mark Roberts, retired director of the Public Health Dynamics Lab, highlights the vulnerabilities of unvaccinated groups such as infants and those with weak immune systems. He underscores that vaccination is crucial not just for personal protection but also for community safety. He compares skipping vaccinations to lacking brakes in a car, emphasizing the risks posed to others.
The AP Health and Science Department receives support from Howard Hughes Medical Institute’s Department of Science Education and the Robert Wood Johnson Foundation. The AP is solely responsible for all content.
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