NEW YORK (AP) — International health experts are meeting this week to determine if the United States and Mexico have forfeited one of their greatest public health victories — the elimination of measles.
Measles is one of the most contagious diseases known to medicine, but vaccines had safely stopped the virus' spread in the U.S. for 30 years. Over those decades, measles had become a medical rarity in the U.S., with deaths from the disease virtually unheard of. But in the past two years, large outbreaks have hit multiple states, spawning thousands of illnesses, including about a dozen deaths.
Experts expect that the meeting, convened by the Pan American Health Organization, or PAHO, will show that measles has officially returned to the U.S. and Mexico — that the virus is now continually spreading within the nations' borders.
"It's a big deal. The decision represents us moving backwards," said Dr. David Margolius, director of Cleveland's health department and a leader in a coalition of big U.S. city health departments.
Here's a look at the meeting's deliberations and why it's important.
International health experts are poring over measles data this week
In a closed-door meeting this week, a PAHO advisory commission is looking at genetic evidence to determine if the same measles virus has been spreading for one year or more in the outbreaks that have torn through North America starting in 2024.
"It's solely based on genetics," said Dr. Amesh Adalja, an infectious disease doctor in the Pittsburgh area and a senior scholar at the Johns Hopkins Center for Health Security.
If so, the commission will say the country can no longer be considered to have "eliminated" measles, meaning a return to sustained circulation of the virus. Last year, PAHO stripped Canada of the measles-free designation it had had since 1998.
The commission will present its determination to PAHO Director Dr. Jarbas Barbosa, a former Brazilian health official, who makes the final determination. An announcement of the findings is being scheduled for next week, PAHO officials said.
The CDC says loss of measles elimination status won't change its approach
A PAHO decision to strip the U.S. of its measles elimination status will not change how federal health officials are addressing outbreaks, CDC Director Erica Schwartz said this week.
"The measles elimination designation is not what protects Americans. Vaccination does. We know where transmission is occurring and we're working with state and local health departments to reach those communities. Losing a designation doesn't mean we abandon an evidence-based approach. It means we remain focused on stopping outbreaks," she said in the statement.
But many public health experts say such an occasion demands a stepped-up, full-throated campaign to promote vaccinations and provide more advice to doctors. They fault what they say is a politically fraught, muted federal response, and blame U.S. Health Secretary Robert F. Kennedy Jr., who was a leading voice in the anti-vaccine movement before President Donald Trump put him in charge of the nation's health agencies.
Kennedy has moved to downsize the childhood vaccination schedule, reshape a key vaccine advisory board, and lauded Trump's executive order calling for spacing out the measles, mumps and rubella vaccine. Such a move runs counter to medical groups' recommendations, and likely would result in fewer children getting fully vaccinated, experts say.
The US is having its worst measles year in decades
Measles typically begins with a high fever followed by a telltale rash that starts on the face and neck. Most people recover, but it's one of the leading causes of death among young children, according to the World Health Organization. Serious complications, including blindness and swelling of the brain, are more common in young children and adults older than 30.
The U.S. achieved measles elimination status in 2000, after decades of vaccination campaigns brought the childhood measles vaccination rate to above 97%. Health experts say a 95% vaccination rate is needed so that when an infected traveler enters a community, so many people are vaccinated that it will not spark an outbreak.
But U.S. vaccination rates have been slipping for years, in part because of disproven claims that the vaccine can cause autism. Trump claimed earlier this year, without evidence, that the MMR vaccine — which is credited with saving millions of lives globally — is possibly "quite lethal." Last year, the childhood vaccination rate fell to about 92% nationally, and was much lower in certain states and certain communities.
Measles exploded last year in large outbreaks in Texas, Arizona, Utah and South Carolina. And the more than 5,100 confirmed cases this year are already double the 2025 tally, driven largely by an outbreak in Pennsylvania that has dwarfed the earlier ones. The U.S. has now seen eight measles-associated deaths this year — more than any year in more than three decades — and is enduring its worst year for measles illnesses since 1991.
At least 50 people have died from measles in Mexico
A measles vaccine did not become available in Mexico until years after a measles vaccine was first licensed — in 1963, in the U.S. — and the U.S. started giving shots. Mexico did not achieve measles elimination status until 2016.
Cases began surging in Mexico early last year. Researchers think an outbreak in the northern border state of Chihuahua stemmed from an unvaccinated Mennonite child from that Mexican state who traveled to Gaines County, Texas, where an outbreak was occurring, and came back infected.
As of this week, more than 20,500 confirmed cases have been reported across the nation. Fifty measles-related deaths have been reported, most of them children younger than 5 years old.
The issue has not been confined to North America. Early this year, the World Health Organization confirmed that Armenia, Austria, Azerbaijan, Spain, the United Kingdom, and Uzbekistan lost their status.
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Associated Press writer Megan Janetsky contributed to this story from Mexico City.
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