A surge in measles cases during the past two years has coincided with a steady slump in MMR immunization rates for children since the start of the COVID-19 pandemic.
Average U.S. vaccination coverage among kindergarten children dropped last year to 92.5%, well below the level of 95% considered necessary to achieve effective "herd" immunity needed to prevent the spread of the virus, the CDC says.
In at least 16 states, some of them with the highest measles incidence this year, vaccine coverage rates have declined to less than 90%, the CDC said.
Many health officials have cited a public backlash to the government's pandemic response and blame U.S. Health Secretary Robert F. Kennedy Jr.'s anti-vaccine policies for further undermining trust in disease-preventing immunizations by embracing unproven theories about vaccine dangers.
Kennedy has repeatedly promoted the claim that measles vaccines are linked to autism despite overwhelming scientific evidence to the contrary. Last June, he fired all members of the CDC's expert vaccine advisory panel, which recommends how vaccines are used and by whom.
"Since early last year, federal leaders have dismissed measles as benign and unavoidable and have spread misleading information about the MMR vaccine," said Andrew Racine, president of the American Academy of Pediatrics.
"Halfway into 2026, the U.S. is experiencing the worst year for measles since 1991. We are witnessing an avoidable crisis that disproportionately hurts children."
As many as 93% of this year's cases were in unvaccinated individuals, with a fraction of the rest having received one or two doses of vaccine before being infected, the CDC said.
Infections were documented by the CDC this year in 45 states and the District of Columbia, with 93% associated with one of 35 new outbreaks reported in 2026, versus 48 last year.
States with the most cases included South Carolina, Utah, Arizona, Texas, Florida, Virginia and Pennsylvania, the CDC says. Just 16 of this year's cases were reported among visitors from other countries.
A South Carolina outbreak sickened nearly 1,000 people over six months after it began in October 2025 to become the largest single-location U.S. outbreak since measles was declared eliminated in the United States in 2000.
That elimination status is now under review, with the Pan American Health Organization delaying a decision until November.
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