The United States is witnessing a worrying rise in measles cases, surpassing the record for 2025 with 2,318 reported cases as of Thursday, according to the Centers for Disease Control and Prevention (CDC). Five months remain in 2026, making it potentially the worst year for measles since 1991. Three significant outbreaks in South Carolina, Utah, and Arizona have led to infections among hundreds, while additional cases appear in other states.

International health officials will convene in November to decide whether the U.S. and Mexico should lose their measles-free status. The U.S. had eliminated local measles transmission by 2000 through high vaccination rates, which recently dropped below the required 95% to prevent outbreaks.

Challenges in Accurate Reporting

Determining the exact pervasiveness of the measles spread presents challenges due to acknowledged undercounting. Individuals often fall ill without seeking medical advice, leading to incomplete case records. Measles is highly contagious, and reduced vaccination rates exacerbate its spread.

Data collected from the 2024-25 school year shows a decline in national vaccination rates for measles, mumps, and rubella to 92.5% among kindergartners, down from 95.2% in 2019-20. In Utah, where cases have exceeded 700 in a year, experts using mathematical modeling and genetic analysis predict the actual outbreak size might be three to four times larger than what’s reported.

South Carolina’s Major Outbreak

South Carolina has faced the country’s largest measles outbreak in 35 years, amassing nearly 997 cases, though officials admit this is likely an undercount. Dr. Brannon Traxler from the state health department notes that the true figure may fluctuate during outbreaks.

Data gaps hinder reliable assessments of an outbreak’s scope. Hospitalization rates can serve as a key indicator, despite not being mandated for reporting across all states. Applied mathematician Damon Toth, involved in Utah’s outbreak analysis, indicates that linking hospitalization percentages with outbreak severity could provide more consistent estimates.

Texas Case Studies

Texas researchers are still evaluating the 2025 outbreak. It could have been nearly twice the size of the 762 documented cases. Remy Pasco from the University of Colorado Boulder notes insufficient vaccination rates as a significant factor in controlling measles.

Dr. Varun Shetty, Texas’ chief state epidemiologist, describes the limitation in reporting accurately due to challenges in verifying household contacts who might have contracted measles. Shetty explains the discrepancies in reported cases often stem from people’s unwillingness to get tested or divulge information to healthcare providers.

The state health department mentioned that 182 probable cases were not confirmed in March 2025 among minors in Gaines County, due to data gaps. Confirmed counts for this outbreak reached 414. Shetty foresees continued outbreaks, stressing the importance of comprehensive vaccination coverage.

Vaccination’s Role in Public Health

Dr. Mark Roberts, a retired director from the University of Pittsburgh School of Public Health, emphasizes the necessity of vaccines to protect vulnerable community members like babies, those with compromised immune systems, and individuals with inadequate immunity from vaccines.

Roberts compares skipping vaccination decisions to refusing safety measures in vehicles. He highlights the communal aspect of vaccination in preventing harm to others beyond oneself.

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