As the United States struggles to contain a resurgence of measles that has swept through swaths of the Southwest, neighboring countries are responding to their own outbreaks.
Canada has reported more than 730 cases this year, making this one of the worst measles outbreaks in the country since it declared the virus “eliminated” in 1998. Mexico has seen at least 360 measles cases and one death, most of them in the northern state of Chihuahua, according to Mexican health authorities.
Many of the communities grappling with measles have large Mennonite populations that public health officials have linked to outbreaks. The multinational resurgence has concerned epidemiologists, who fear that simultaneous outbreaks near the U.S. border will make it more difficult to contain the virus.
“It’s just a line on the map that separates them — we share air, we share space,” said Lisa Lee, an epidemiologist at Virginia Tech.
Falling vaccination rates have left the United States more vulnerable to the highly contagious virus, she added. “If we don’t have a buffer or herd immunity to keep the virus out,” she said, “we will be at risk as long as any of our neighbors are at risk.”
The outbreak in the Southwest shows no signs of slowing. Since late January, the virus has sickened more than 560 people in Texas, 63 people in neighboring New Mexico, and a dozen people in Oklahoma.
More than 30 cases have been reported in Kansas, which public health officials believe may be linked to the Texas outbreak. Alarmed, officials in several states have issued warnings to their residents.
The governor of Nebraska released a measles response plan though the state hasn’t yet reported any cases. New York State officials earlier this month issued a travel advisory about trips to Ontario and several U.S. states, warning that measles is “only a car ride away.”
The virus has spread so widely in North America this year that the Pan American Health Organization published an alert in late February, warning that the region’s elimination status was at risk if nations did not strengthen their vaccination and outbreak response efforts.
A risk assessment by the organization concluded that measles posed a “high” risk to public health in the Americas.
The outbreak in Canada, which began in late 2024, has been “disproportionately affecting” people from Anabaptist communities, including Mennonite and Amish people, and can be traced back to a large Mennonite gathering in the fall, according to the Ontario Ministry of Health.
The largest outbreak in the United States began in a Mennonite community on the western edge of Texas. Areas with smaller outbreaks, like Oklahoma and Southwest Kansas, also have sizable Mennonite communities, according to Steven Nolt, who studies Mennonite and Amish groups at Elizabethtown College in Pennsylvania.
There is no religious doctrine in the Mennonite faith that bars vaccination; however, many in the community avoid interacting with the medical system and adhere to a long tradition of natural remedies.
Highly contagious viruses, like measles, take root in close-knit, undervaccinated communities. In 2019, measles spread through a large Orthodox Jewish population in what became the largest outbreak in recent U.S. history.
Even if the virus doesn’t break into the broader community, measles can infect hundreds by hopping between pockets of vulnerable people. Outbreaks have the potential to spread over country borders and hundreds of miles if the virus finds a network of unvaccinated communities.
That appears to be part of the story in the current measles resurgence. The virus was first brought into a Mennonite community in Chihuahua by a 9-year-old boy who visited Texas with his family, according to Rodolfo Cortés, a spokesman with the state’s health ministry.
Mennonite groups across North America are extremely interconnected, Dr. Nolt said. While he’s unaware of large, organized gatherings between the groups, he said that Mennonites will often cross borders to visit extended family.
While no firm link has been established to the Canadian cases, the same virus type has been detected in all three countries, according to data presented this week at a Centers for Disease Control and Prevention meeting.
Measles cases have not been confined to Mennonite communities, however. More than half of U.S. states have reported at least one case this year, and there have been outbreaks in Ohio and Indiana with no known connections to other outbreaks.
In a public meeting Tuesday, David Sugerman, a C.D.C. senior scientist, said recent threats to local public health funding meant the agency was now “scraping to find the resources” to support Texas and other states grappling with outbreaks.
On average, each measles case costs between $30,000 and $50,000 in public health response work, he said.
While there have for decades been insular, undervaccinated communities, Dr. Lee said the people surrounding those groups have generally had high immunization rates. But in recent years, national childhood vaccination rates have fallen.
“That ring around those groups are not protected.” she said. “And so there is, for lack of better words, leakage out into communities.”
