Another measles-related death has occurred in Pennsylvania, marking the fourth one in just a matter of weeks. Yesterday the Mifflin County coroner announced an 18-year-old resident died “due to complications of measles,” which was identified acute disseminated encephalomyelitis (ADEM).1
No other information about the teen was shared by the coroner or the state health department. Just a few days ago, the Jefferson County, PA coroner announced a measles death in a 40-year old woman who was unvaccinated.
“My thoughts are with the two families who lost loved ones to this highly-contagious virus, as Pennsylvania faces the worst measles outbreak in more than three decades,” Secretary of Health Debra Bogen, MD, said in a statement. “We remain committed to working with our partners across Pennsylvania to stem this outbreak and prevent more deaths. That means ensuring people have the facts about measles and access to the MMR vaccine—which kept measles outbreaks at bay for decades.”
What You Need to Know
Pennsylvania is experiencing its worst measles outbreak in over three decades, with 693 cases across 38 counties and four deaths so far (an 18-year-old, a 40-year-old woman, and two infants), the state's first measles deaths since 1991.
The 18-year-old's death was linked to acute disseminated encephalomyelitis (ADEM), a rare but often fatal measles complication that mostly affects children over 4 and typically strikes days to weeks after infection.
Because infants can't get their first MMR dose until around age 1, they depend on community herd immunity (roughly 95% vaccination coverage) for protection, making the outbreak especially dangerous for the youngest residents.
In Pennsylvania, this marks the fourth measles-related death in just the last few weeks, and the first time since 1991 that there has been deaths in the state. In 2025, there were 3 reported measles-related deaths across the entire nation, without any deaths in Pennsylvania.
Pennsylvania is in the throes of its worst measles outbreak in decades. As of yesterday, the department of health was reporting 693 cases in 38 of the 67 counties in the state. In late August, the state had reported 393 cases in 28 counties, so there has been a 300 case increase in just a few weeks.
What is ADEM?
This complication is rare, occurring in 1 of every 1000 cases, and mostly in children over the age of 4 years. The disease onset is acute and usually occurs within days to weeks after measles, and is often fatal.2
Herd Immunity Offers Community Protection
Within the last few weeks, Pennsylvania health officials reported 2 measles-related deaths in babies. One was a newborn who died shortly after birth and the other was a 6-week old.
Typically the first dose measles, mumps, and rubella (MMR) vaccines are not administered until a child is about 1 years old. So, neonates and young babies need outside protection from the local community with herd immunity from people who have been vaccinated already. Without herd immunity, all people who are not vaccinated are vulnerable to the measles. To achieve herd immunity in local communities, the MMR vaccine rate needs to be approximately 95% of the population.
2.Griffin, D. E. (2014). Measles virus and the nervous system. In Handbook of Clinical Neurology (pp. 577-590). (Handbook of Clinical Neurology; Vol. 123). Elsevier B.V.. https://doi.org/10.1016/B978-0-444-53488-0.00027-4
