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More than 17,000 infections have been confirmed in that period, four times the number in the United States. Measles is largely preventable with two shots of a common vaccine. But most of those with infections hadn’t gotten it.
Mexico’s ongoing measles outbreak offers a case study of what can happen when a country’s vaccine coverage slips. The disease was first identified in the 9-year-old’s neighborhood, in a secluded Mennonite community of apple, wheat and corn farms in Chihuahua state, south of Texas, authorities said. It spread to agricultural laborers, many of them from Indigenous communities.
By the end of 2025, this Mexican state, roughly the size of Michigan, had confirmed around 4,500 cases – more than in the entire United States.
Pinning down the movement of a microscopic pathogen can be difficult. But Mexican authorities believe that the measles virus probably arrived in the throat or lungs of the third-grader, who was unvaccinated, and then spread wildly.
In Chihuahua, officials did genetic tests on more than 100 cases. Each came back with the stamp of the measles virus that popped up in Canada in 2024 and later appeared in Texas: genotype D8 and lineage MVs/Ontario.CAN/47.24. The virus has since traveled through Mexico’s 32 states.
Scenes of the Mexican countryside near Cuauhtemoc, where Mennonite community has extensive farmland in Cuauhtemoc where they cultivate apples, corn and wheat. These farmworkers were part of the chain of spread of measles. Mary Beth Sheridan/CNN
“Everything comes from the outbreak in Chihuahua,” said Dr. Miguel Nakamura, director of epidemiological information at Mexico’s Health Ministry.
In the United States, a series of measles outbreaks starting in Seminole raised concerns about the growing role of vaccine skeptics in the government.
Mexico’s case is somewhat different. The president, Claudia Sheinbaum, is a leftist with a PhD in engineering who prides herself on her scientific background. What unites the neighboring nations’ outbreaks is something else, epidemiologists say: complacency.
Measles was declared eliminated in both countries more than a quarter-century ago – a historic public-health achievement. But Mexico’s once-robust vaccine program has atrophied amid disarray in its government-dominated health system, say epidemiologists.
“This is the paradox,” said Samuel Ponce de León, an epidemiology professor at the National Autonomous University of Mexico. Thanks to the success of vaccines, “you don’t see kids with signs of polio or complications from measles, like deafness or meningitis. We stopped having measles cases, so people began to say, ‘Why should I worry?’”
Measles is one of the most contagious diseases in the world, far more so than Covid-19. It’s spread by an infected person coughing, sneezing or even just talking. The virus can hang in the air for up to two hours. A single person can potentially infect 18 others.
Measles can lead to serious complications and even death by triggering pneumonia or brain swelling. Bergen quickly realized that the illness was like nothing his kids had had before. One son was so pained by sunlight that his father covered the windows in black plastic. Another went limp. “He couldn’t even drink water at night by himself,” Bergen recalled.
But after the family left Seminole, the virus exploded. In the following months, more than 760 people in the Texas town were infected, and 99 were hospitalized, according to the state health department. Two girls died. (An unvaccinated New Mexico man who also died tested positive for measles, in a related outbreak.)
Many cases are mild. The 9-year-old who returned from Seminole developed a high fever and rash but quickly got better and returned to school, said his mother, who spoke with CNN on the condition of anonymity.