As the U.S. marks a year of measles outbreaks, is the disease back for good?

"The U.S. had been virtually free of the disease for more than a quarter-century thanks to highly effective and safe vaccines, but now experts say we're on track to losing that status if officials determine measles has spread continuously for a year. The U.S. is in the throes of the deadliest measles outbreak it has seen in decades, says Jennifer Nuzzo, an epidemiologist and director of the Pandemic Center at Brown University."

"Losing measles elimination status is an official acknowledgement that the country is on the wrong path. For measles, the Pan American Health Organization (PAHO) formally declares a country has eliminated the disease when cases can no longer be linked to one anotherthere is zero continued transmissionfor 12 months or more. Last November the Americas officially lost their elimination status when PAHO's review of epidemiological data revealed that Canada was no longer measles free for a year."

Measles began ripping through West Texas in January 2025 and has spread across multiple U.S. states, Mexico, and Canada. Prior to this resurgence, the United States had been virtually measles-free for more than a quarter-century because of highly effective, safe vaccines. Pan American Health Organization rules require zero linked transmission for 12 months to declare elimination; continuous transmission for a year would end the U.S. elimination status. The Americas lost elimination last November after epidemiological review found Canada had ongoing transmission for a year. Loss of elimination is a public-health signal but can be reversed with intensified vaccination, strengthened surveillance, and rapid outbreak response.

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