As measles continues spreading across the U.S. at a pace not seen in decades, physicians are warning about a rare but often fatal neurological complication that can emerge years after initial infection, KFF Health News reported March 13.
Subacute sclerosing panencephalitis, or SSPE, occurs when the measles virus reactivates in the brain, sometimes years after a person is infected.
Researchers estimate about 1 in 10,000 people who contract measles will develop SSPE, with children who contract the virus before age 5 facing a significantly higher risk. The condition is almost always fatal.
Concern about the complication has grown alongside the national resurgence in measles. The CDC has confirmed 1,281 measles cases nationwide as of March 5. That is more than half of the 2,283 cases confirmed last year in just the first three months of 2026, with a large outbreak in South Carolina driving about half of this year’s cases.
“We are likely to see SSPE cases going forward, especially if we don’t get this under control,” Adam Ratner, MD, a member of the American Academy of Pediatrics’ Committee on Infectious Diseases, told KFF Health News.
In January, the Child Neurology Society shared an educational video for clinicians on SSPE, as the condition has been largely unseen in the U.S. since the widespread adoption of measles vaccination.
Aaron Nelson, MD, a professor of neurology at NYU Grossman School of Medicine in New York City, noted that there is not a reliable way to predict who will develop the complication, and that no effective treatments exist.
“The one best thing that we can do, ideally, is to prevent children from having to go through it in the first place,” Dr. Nelson told the publication.
About 77% of measles cases this year have involved children and adolescents, the majority of whom were unvaccinated or had an unknown vaccination status.
Two doses of the measles vaccine lowers an exposed person’s risk of contracting the virus from 90% to 3%, according to the report.
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