U.S. Faces Surge in Measles Cases Amidst Declining Vaccination Rates

The number of measles cases in the United States has exceeded the total recorded in all of 2025, even with several months remaining in 2026. The U.S. Centers for Disease Control and Prevention (CDC) reported 2,318 measles cases as of Thursday, surpassing the 2,289 cases reported in 2025. This marks the highest count in over thirty years.

Major outbreaks in states like South Carolina, Utah, and Arizona have led to hundreds becoming ill, while smaller case clusters have emerged in other regions. In November, international health officials plan to assess whether the U.S. and Mexico maintain their measles-free status, which both nations eradicated locally in 2000 by sustaining high vaccination levels. These rates have recently dropped below the 95% threshold necessary to avert outbreaks.

“Maintaining high vaccination coverage is crucial not only for individuals but for the health of entire communities,” noted Dr. Varun Shetty, Texas’ chief state epidemiologist.

Undercounting of Cases

Undercounting of measles cases in the U.S. complicates understanding the true extent of the spread. Many individuals experience symptoms but do not seek medical treatment. This skews official counts and is a common issue with various diseases.

Experts suggest the actual spread may be broader than current data reveals, primarily due to the highly contagious nature of the virus coupled with declining national vaccination rates. During the 2024-2025 school year, vaccination rates for measles, mumps, and rubella fell to 92.5% among kindergartners, compared to 95.2% in 2019-2020. Certain communities report even lower vaccination rates.

Case Studies: Utah and South Carolina

In Utah, over 700 people have contracted measles in the past year, according to the state health department. Epidemiologist Dr. Leisha Nolen indicates that the outbreak along the Utah-Arizona border might be up to four times larger than currently documented estimates.

South Carolina recorded its largest outbreak in 35 years, with official numbers listing 997 cases. However, the true count is likely higher, though how much higher remains unknown. Dr. Brannon Traxler, acting director of the state department of health, states, “The extent of undercounting is impossible to know and may vary during the outbreak.”

Measuring Outbreaks with Limited Data

Accurate assessments of an outbreak’s scope are challenging due to data deficiencies. Hospitalization rates can provide insights, yet states vary in requiring measles hospitalization reports.

“If we had a standardized measure of all hospitalization cases, it would help verify outbreak sizes against other evaluation methods,” said Damon Toth, a mathematician at the University of Utah’s medical school.

Research in Texas

Researchers in Texas continue analyzing the 2025 measles outbreak, where early results suggest twice as many cases as the 762 officially reported. Rémy Pasco, a mathematical epidemiologist, emphasizes that inadequate community vaccination leaves few options for controlling measles.

Dr. Shetty identifies instances where infected individuals tested positive yet it was unclear whom they lived with or whether those individuals also became ill. “What we’re able to count and report often underestimates the actual situation,” Shetty expressed, as it depends on people’s willingness to undergo testing and share information.

Importance of Vaccination

Dr. Mark Roberts, former director of the Public Health Dynamics Lab, underscores the impact on “innocent bystanders” — those unable to receive vaccines such as infants and immunocompromised individuals. His research suggests these groups face significant risks during outbreaks.

Roberts equated vaccination to car safety: “Not vaccinating is like driving without brakes; it’s not only about personal safety but also for others on the road.”

Despite challenges, high vaccination remains critical for public health. Sustained efforts are necessary to ensure community protection and reduce measles transmission risks.