U.S. measles elimination status at risk as cases hit highest level since 1991

International health authorities announced they will meet April 13 to determine whether the United States has lost its measles elimination status, a certification granted in 2000 that appears in jeopardy following a year-long outbreak that infected 2,242 people across 44 states. The assessment comes as the U.S. records the highest measles case count since 1991, with nearly 50 separate outbreaks documented and cases confirmed in multiple states showing potential signs of continuous transmission.

The reexamination hinges on a technical threshold: whether a single chain of measles has spread uninterrupted within the U.S. for at least 12 months. But public health experts agree the underlying problem extends beyond this definition — vaccination rates have fallen below the 95% level needed to stop the virus’s spread, leaving communities vulnerable to a disease that public health authorities declared eliminated more than two decades ago.

If the Pan American Health Organization votes to revoke the U.S. elimination status, the U.S. would become the second North American nation to lose the designation, following Canada. More broadly, the decision would underscore a public health crisis driven by declining vaccination rates, barriers to health care access, and escalating vaccine hesitancy fueled by misinformation and federal messaging that has cast doubt on vaccine safety.

The Outbreak in Texas and Cross-Border Spread

The outbreak began in rural West Texas on January 20, 2025. Within weeks, it had spread dramatically, particularly in Gaines County, where 762 confirmed measles cases were documented and two children died. Health officials documented evidence suggesting a significant undercount — 182 additional potential measles cases in Gaines County went unconfirmed in March 2025, suggesting the true number may have been roughly 44% higher than reported.

The same measles strain subsequently appeared in New Mexico, Utah, Arizona, and South Carolina. It also crossed the border into Mexico, where it triggered an outbreak that has sickened 6,000 people and killed 21 in Chihuahua state alone. The Mexican outbreak began when an 8-year-old boy from Chihuahua traveled to Seminole, Texas, and returned home infected.

Measles Contagiousness and Declining Vaccination Rates

Measles is one of the most contagious pathogens known. It infects 9 of every 10 unvaccinated people who are exposed to it. Stopping its spread requires a vaccination rate of 95% within a community — a threshold the U.S. has not met nationally. The Centers for Disease Control and Prevention reported a national vaccination rate of 92.5%, with many communities falling well below that critical level.

“The bottom line is the conditions are sufficient to allow this many cases to occur,” said Dr. Jonathan Temte, a Wisconsin family physician who helped certify the U.S. was measles-free in 2000. “And that gets back to de-emphasizing a safe and effective vaccine.”

Experts attribute the decline in vaccination rates to multiple factors: parental vaccine waivers, restricted access to health care, and widespread misinformation about vaccine safety. More recently, Trump administration health officials, including Health Secretary Robert F. Kennedy Jr., have questioned and cast doubt on the safety of vaccines while also defunding local efforts to improve vaccination rates.

A Department of Health and Human Services spokesperson said Thursday that Kennedy has emphasized vaccines as the best way to prevent measles, and that the CDC is responding to outbreaks and working to increase vaccination rates. During a briefing Tuesday, department officials said they do not yet have evidence of a single continuous chain of measles transmission lasting 12 months.

Expert Assessment: The Path Forward

Public health officials say the full scope of the outbreak likely exceeds confirmed case counts. Many people living in outbreak areas face barriers to health care access and distrust of government institutions, leading them to avoid testing. Contact tracing — the work of identifying and monitoring exposed people — has become increasingly difficult and expensive. A single measles case can cost public health departments tens of thousands of dollars to investigate.

“The U.S. has changed its investment in public health, so we’re less able to do the case tracking that we used to do,” said Noel Brewer, a behavioral scientist who chairs the U.S. committee that will finalize the outbreak data for international health officials.

Dr. Andrew Pavia, a Utah physician and longtime CDC consultant, expressed skepticism that continuous transmission could be ruled out. “My best guess is we will lose elimination status,” Pavia said. “The case for this not being continuous transmission is tenuous, and I think they are likely to err on the side of declaring it a loss of elimination status.”

Genetic sequencing has confirmed the same measles strain across multiple states and international borders, including in Canada and Mexico. But genetic similarity alone cannot definitively prove continuous transmission, as the measles virus mutates relatively slowly compared to other pathogens.

Sebastian Oliel, a Pan American Health Organization spokesperson, indicated the organization would apply conservative standards in interpreting ambiguous evidence. “When there is a case of unknown origin in a country with ongoing local spread,” Oliel said, “the most conservative approach is to consider the case part of the existing national transmission.”

Throughout 2025, measles spread far beyond Texas. New Mexico confirmed 100 cases with one adult death. Kansas documented nearly 90 cases across 10 counties over seven months. Ohio confirmed 40 cases. Montana, North Dakota, and Wisconsin each recorded 36 cases.

Most concerning, more than 800 measles cases have been confirmed across Utah, Arizona, and South Carolina since late summer, with no indication the outbreaks have peaked.

Health officials remain uncertain about 2026 trends. “2025 was the year of measles,” Brewer said. “Will 2026 be the year of rising or falling measles cases? Does it get worse or does it get better? No one knows the answer.”