A Surge in Measles Cases Raises Concerns in the U.S.
The U.S. is experiencing a significant measles outbreak, with Arizona notably affected, as the number of cases in 2026 has already surpassed the previous year’s record. With five months remaining in the year, the Centers for Disease Control and Prevention (CDC) report over 2,318 cases, marking the highest count in more than three decades.
The outbreak is largely concentrated along the Arizona-Utah border, where mathematical models and genetic studies suggest the true number of cases could be three to four times higher than reported, according to Utah epidemiologist Dr. Leisha Nolen. This discrepancy arises due to unreported infections.
In 2025, the U.S. recorded 2,289 measles cases, the highest in over 30 years, but 2026 has already topped this with several months to go. Besides Utah and Arizona, South Carolina has experienced a large outbreak, alongside smaller clusters in other states.
In November, international health officials are set to convene to assess whether the U.S. and Mexico will lose their measles-free status, achieved in 2000 through high vaccination rates that have since dropped below the 95% threshold needed to prevent outbreaks.
Undercounting of Measles Cases
Despite rising numbers, the actual spread of measles remains uncertain. Experts acknowledge that official counts are incomplete as some individuals do not seek treatment when infected. The virus’s high contagion level and declining vaccination rates further complicate accurate assessments. For instance, national vaccination rates for the measles, mumps, and rubella (MMR) vaccine among kindergartners fell to 92.5% in 2024-25 from 95.2% in 2019-20.
In Utah, more than 700 people have been affected by measles over the past year, as reported by the state health department. Meanwhile, South Carolina’s outbreak, the largest in 35 years, might be an undercount, though the extent is unknown.
Wastewater samples from Sedona tested positive for the measles virus, suggesting recent infections in the area.
Dr. Brannon Traxler from the state department of health notes that the undercount is “impossible to know and may vary during the course of an outbreak.” This lack of clarity makes it challenging to determine the outbreak’s true size. Hospitalization rates could provide insights, but not all states require reports on measles hospitalizations.
Continuing Analysis of Past Outbreaks
Researchers are still evaluating the 2025 Texas outbreak, which may have been nearly twice as large as the reported 762 cases. Rémy Pasco from the University of Colorado Boulder mentions that undercounts aren’t surprising in the absence of a 95% community vaccination rate.
Dr. Varun Shetty, Texas’ chief state epidemiologist, highlights challenges in confirming cases when individuals are unwilling or unable to get tested or provide information. In Gaines County, 182 probable cases in minors went unconfirmed due to insufficient data, while the confirmed count was 414.
Shetty warns that without widespread vaccination, measles cases and outbreaks will likely continue, emphasizing the importance of high vaccination coverage for community protection.
Vaccination: A Broader Responsibility
Dr. Mark Roberts, former director of the Public Health Dynamics Lab at the University of Pittsburgh, emphasizes the broader societal impact of vaccination. His research indicates that those unable to get vaccinated, such as young infants and individuals with compromised immune systems, are most vulnerable during outbreaks.
Roberts likens skipping vaccination to not using brakes in a car, as it endangers not only the individual but also others. “Not vaccinating your kid is like saying, ‘I don’t want my car to have brakes,’” he said, highlighting the communal nature of disease prevention.
For more information on the outbreak and vaccination efforts, refer to the following resources: AP News – Measles Outbreak, AP News – Measles-Free Status, AP News – Vaccination Rates.
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