An unvaccinated 18-year-old from Mifflin County has died of acute disseminated encephalomyelitis (ADEM), a rare inflammation of the brain and spinal cord linked to measles, according to Mifflin County Coroner Andrea Alcalde. The Pennsylvania Department of Health confirmed the death on Tuesday, along with the death of an unvaccinated Jefferson County woman. That brings the state's count of measles-associated deaths this year to four.
After reviewing medical records and other investigative information, Alcalde determined that the cause of death was "acute disseminated encephalomyelitis, a rare and severe neurological complication of measles," according to a news release reported by CBS News Pittsburgh. The manner of death was ruled natural. State Health Secretary Dr. Debra Bogen said Pennsylvania is facing its worst measles outbreak in more than three decades.
The four deaths have involved very different patients. Pennsylvania's first two measles-associated deaths, announced in late August, were infants in Lancaster County, and the county coroner has said measles caused only one of them. The Jefferson County woman was 40 and had chronic obstructive pulmonary disease (COPD) and asthma. The Mifflin County case involves an older teen, and the coroner tied the death to a complication affecting the brain and spinal cord.
A Rare Complication That Can Appear After Recovery Begins
ADEM is an immune reaction in which the body attacks myelin, the protective coating around nerve fibers in the brain and spinal cord. It usually develops days to weeks after an infection, so a person may seem to be improving before neurological symptoms start.
Measles can cause serious brain complications. The CDC estimates that about 1 in every 1,000 children who get measles will develop encephalitis, or swelling of the brain, which can lead to convulsions, deafness, or intellectual disability. About 1 in 5 unvaccinated people in the United States who get measles is hospitalized, and pneumonia is the most common cause of measles death in young children.
Beyond the county of residence and vaccination status, officials have released few details about the 18-year-old.
Central Pennsylvania Joins the Outbreak Map
Mifflin County is a newer part of the outbreak. On Sept. 14, the Department of Health said a person who tested positive for measles may have exposed others at an ALDI supermarket at 339 Freedom Ave. in Burnham on Sept. 3, between 9 a.m. and 2 p.m. The department urged anyone who may have been exposed to check their vaccination status and watch for symptoms.
Statewide, the Department of Health reported 693 confirmed cases across 38 of Pennsylvania's 67 counties as of Sept. 14, with 133 hospitalizations. Four cases, less than 1% of the total, were in vaccinated people. State health workers have given nearly 4,300 MMR doses at 130 pop-up clinics since the outbreak began in late April. Providers across the state gave more than 46,000 MMR doses in August, compared with about 25,000 in a typical month.
Nationally, CDC data show 3,294 confirmed measles cases in 2026 as of Sept. 10, and 95% of them are linked to outbreaks. MMR vaccination coverage among U.S. kindergartners has fallen from 95.2% in the 2019-2020 school year to 92.4% in the 2025-2026 school year, leaving about 280,000 kindergartners at risk.
State and Federal Death Counts Still Differ
The state's count changed quickly. The department's Sept. 14 update listed two confirmed measles-associated deaths and said officials were reviewing a possible third death reported by the Jefferson County coroner on Sept. 13. MedicalDaily previously reported on the Jefferson County woman's death. According to family members, she declined measles testing before she died. A nasal swab taken at the time of her death later tested positive, and the state confirmed that death on Tuesday.
Pennsylvania counts a death as measles-associated only when the person tested positive for measles, died within 30 days of rash onset, and did not die of an unrelated cause. On Sept. 10, the department shared that definition with the CDC and the Council of State and Territorial Epidemiologists (CSTE), the group that develops uniform disease definitions in the United States.
The CDC's national measles page says the National Center for Health Statistics does not have any 2026 death records that list measles as the underlying cause. The agency says it is working with CSTE on a standardized definition for measles deaths. Until that work is finished, state and federal death counts may continue to differ.
Steps for Families in Affected Counties
Families in the 38 counties with confirmed cases can take a few concrete steps now. Make sure everyone in the household has two documented MMR doses, which are about 97% effective at preventing measles. Ask a pediatrician whether an early MMR dose is recommended for an infant younger than 12 months who lives in or is traveling to an outbreak area. Adults who are unsure of their vaccination status can ask a clinician whether another dose or a blood test to check immunity makes sense.
Measles symptoms can start seven to 21 days after exposure. They usually begin with fever, cough, runny nose, and red, watery eyes, followed by a rash that starts on the head and spreads downward. Anyone with those symptoms should call a health care provider before arriving so the office can keep other patients from being exposed.
This case also points to warning signs that can appear later. A person who recently had measles and then develops new confusion, a severe headache, vision changes, trouble walking, weakness, or a seizure should get urgent medical care, even if the rash and fever are gone. This is general information, not a diagnosis.
MMR vaccine is available through health care providers, county and municipal health departments, state health centers, federally qualified health centers, and the Vaccines for Children program, which provides vaccines at no cost to eligible children. People who believe they were exposed and have symptoms can call the state hotline at 877-PA-HEALTH (877-724-3258). County-level case counts are posted on the state measles dashboard. MedicalDaily will continue to track both the state and federal counts.
Key Questions Answered
What happened? The Mifflin County coroner determined that an unvaccinated 18-year-old died of acute disseminated encephalomyelitis, a rare neurological complication of measles. The Pennsylvania Department of Health confirmed the death on Sept. 15. It is the state's fourth measles-associated death of 2026.
What is ADEM? It is an immune reaction that inflames the brain and spinal cord and damages the protective coating around nerve fibers. It usually appears days to weeks after an infection.
How large is the outbreak? Pennsylvania reported 693 confirmed cases in 38 counties and 133 hospitalizations as of Sept. 14. Nationally, the CDC counted 3,294 confirmed cases as of Sept. 10.
Why does the national death count differ? The CDC says the National Center for Health Statistics has no 2026 death records listing measles as the underlying cause. The agency is working with state epidemiologists on a standardized definition.
Who faces the highest risk? Unvaccinated people are most at risk of infection. The CDC says children younger than 5, adults older than 20, pregnant women, and people with weakened immune systems are more likely to have complications.
What warning signs matter after measles? New confusion, a severe headache, vision changes, trouble walking, weakness, or a seizure call for urgent medical care, even after the rash clears.
Where can families get vaccinated? Through health care providers, county and municipal health departments, state health centers, federally qualified health centers, and the Vaccines for Children program. The state hotline is 877-PA-HEALTH.
