The number of measles cases in the U.S. this year is nearing a 30 year high.

That number has quadrupled compared to 2023. As of Friday, according to the CDC, there have been 1,168 confirmed cases across 33 states nationwide. Most cases are in unvaccinated people.

There are also new challenges to addressing the spread of measles: according to a Johns Hopkins University study published this week, rates of childhood vaccination against measles fell broadly across the U.S. in the wake of the COVID-19 pandemic.

Childhood vaccination for measles dropped in close to 80% of counties, according to available data for more than 2,000 counties nationwide. The decline includes states that are actively battling outbreaks of the disease.

Domestic and international travel both contribute to the spread of the disease, experts say. U.S. health officials in June directed Americans to get vaccination against measles if they were participating in international travel, no matter their destination or itinerary.

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Three people have died in 2025's national outbreak.

The outbreak also threatens to reverse measles' formal elimination in the U.S. If the outbreak continues until January of 2026, measles will no longer be considered eliminated — a designation that requires 12 months with no local transmission of the disease.