A rare brain complication linked to measles has killed an 18-year-old in Pennsylvania, marking the state’s fourth death in a surge of cases this year. The teen from Mifflin County died from acute disseminated encephalomyelitis (ADEM), a condition where the immune system attacks the brain and spinal cord after infection. The Mifflin County coroner confirmed the cause in a Facebook post, noting the damage typically appears days to weeks after the initial illness.
ADEM often begins with symptoms resembling a viral infection, fever, headache, nausea, and vomiting, but quickly worsens into confusion, unusual sleepiness, weakness, or vision changes. In severe cases, it can lead to seizures or balance problems. Doctors emphasize that early medical attention is critical, as treatment is most effective when started promptly.
The condition affects fewer than 1 in 100,000 children annually, but before vaccines, measles was its most common trigger. While other viruses can also cause ADEM, the outcomes for measles-linked cases were historically worse. Today, the complication more often follows common respiratory or stomach infections.
None of Pennsylvania’s four measles deaths this year involved vaccinated individuals. Two infants in Lancaster County died last month, both too young for the MMR vaccine under current guidelines. A 40-year-old woman in Jefferson County also died from measles complications last week.
Pennsylvania has recorded nearly 700 measles cases across 38 counties in 2026, with about 100 new cases reported in the past week alone. The state’s last measles deaths occurred in 1991, and the current outbreak is the worst in over three decades. Nationally, 2026 is the first year with more than seven measles-related deaths in two years, a sharp rise from the previous three decades.
Vaccination rates have fallen below the 95% coverage needed to prevent outbreaks, reversing progress made after the U.S. declared measles eliminated in 2000. International health officials will reassess in November whether the U.S. and Mexico still meet measles-free standards.
Acute disseminated encephalomyelitis is a severe but rare complication of measles, one that can be prevented through vaccination. The state health department has urged residents to ensure they and their children are up to date on the MMR vaccine, which has kept measles outbreaks under control for decades.
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