A measles outbreak in Utah has become the longest-running active outbreak in the United States, raising concerns among public health officials as the country risks losing a public-health milestone it has maintained for a quarter century, reports the Wall Street Journal.
The outbreak has reached 679 cases and has persisted for more than a year, making it the latest and longest-lasting in a series of measles outbreaks reported across the country since early 2025, according to information reviewed by The Wall Street Journal.
The Centers for Disease Control and Prevention is assessing whether any U.S. measles outbreaks have lasted longer than 12 months, a key benchmark used to determine whether the nation has maintained its measles elimination status.
Utah has recorded one of the nation's largest and longest-running measles outbreaks, with transmission stretching from 2025 into 2026. The outbreak has sickened more than 600 people and has been linked to declining vaccination rates and clusters of unvaccinated residents, placing significant pressure on hospitals and public health officials.
The United States declared measles eliminated in 2000, meaning the disease was no longer spreading continuously within the country. While imported cases and localized outbreaks have occurred since then, health officials have largely been able to prevent sustained transmission.
Under international public health standards, continuous transmission of the virus for more than 12 months could jeopardize that designation.
The CDC is reviewing outbreak timelines to determine whether the threshold has been crossed, according to the Journal. Federal health officials have not yet announced any change to the nation's elimination status.
The Utah outbreak highlights a broader resurgence of measles in the United States, where health experts have warned that declining childhood vaccination rates and growing pockets of unvaccinated residents have increased the risk of outbreaks.
Measles is one of the world's most contagious diseases.
The virus spreads through the air and can linger in a room for up to two hours after an infected person leaves, according to the CDC. Symptoms typically include fever, cough, runny nose, and a characteristic rash. In severe cases, measles can lead to pneumonia, brain swelling, and death.
Public health officials say the measles, mumps, and rubella vaccine remains highly effective at preventing infection and severe illness.
The Utah outbreak is the latest challenge for health authorities seeking to contain the virus and preserve the country's elimination status.