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By Nat Lash and Patricia Callahan, ProPublica | June 8, 2026
American children lined up for the world’s first measles shots in the early 1960s, but it took nearly 40 years of shoring up immunization programs before the infamous contagion had been so thoroughly controlled that a panel of experts declared in 2000 that the United States had eliminated measles within its borders.
For a quarter century, the U.S. only saw outbreaks when infected travelers brought the virus in from abroad. The resulting waves of measles didn’t last more than a year. Those days are gone.
Measles began tearing through the dusty plains of West Texas in January last year, and since then, all but a handful of states have seen cases. Two unvaccinated Texas girls and an adult across the border in New Mexico died before the West Texas outbreak seemed to burn out last July. By then, measles was popping up in Utah, and state health officials couldn’t tell where the earliest patients had caught the virus.
The Texas and Utah cases now sit at the center of an unusually technical, and politically fraught, question: whether the United States will lose its measles-free distinction. Countries aren’t penalized for losing the status, but it’s an indication of cracks in a nation’s once rock-solid immunization programs, a loss of faith in vaccines among its people, or both.
To have any chance of keeping the designation, the U.S. will need to make a strong case that measles didn’t spread endemically, meaning person to person in a continuous chain within the country for more than a year. For clues, the Centers for Disease Control and Prevention is analyzing the full genetic code of measles viruses that infected patients.
ProPublica embarked on its own analysis, reviewing over 1,800 whole genome sequences, including those released as recently as last month, to compare the genetic fingerprints of measles viruses circulating in the U.S. and Canada. This showed that the measles virus still spreading in Utah as of this May is very closely related to the one that sickened Texans over a year ago.
ProPublica’s analysis isn’t a smoking gun that proves endemic spread, but given how similar the viruses are, it will be difficult for the U.S. to prove measles isn’t endemic, “unless CDC has something up their sleeves,” said Dr. Alberto Severini, a retired molecular virologist and measles expert who spent two decades at Canada’s Public Health Agency.
With the midterm elections approaching, the spread of measles has become a political liability for President Donald Trump, who picked the founder of an antivaccine organization to be his health secretary. Since Trump’s inauguration last year, there have been more than 4,300 U.S. cases, a high not seen in three decades.
Read ProPublica’s full investigation, including their detailed genomic methodology, interactive family-tree graphics and CDC and HHS responses, at the original story: What ProPublica Found in the Genetic Code of America’s Measles Outbreaks.
This story was originally published by ProPublica, a Pulitzer Prize-winning nonprofit newsroom that investigates abuses of power, and is republished here under ProPublica’s Creative Commons license.