The measles outbreak in Pennsylvania has reached a fourth reported death, adding to growing public-health concerns in the United States as measles infections continue to spread across multiple states.

Pennsylvania health authorities reported that an 18-year-old from Mifflin County died after developing acute disseminated encephalomyelitis, a rare neurological complication associated with measles. The individual had not received a measles vaccine.

The latest death follows three earlier measles-associated deaths in Pennsylvania, including two infants and an adult. The state’s outbreak has now involved nearly 700 cases across 38 counties, with approximately 100 additional cases reported during the previous week.

The wider U.S. outbreak has also expanded significantly. The country has recorded more than 3,000 confirmed measles infections in 2026, making this the largest measles outbreak in the United States in decades.

Measles is highly contagious and can cause complications involving the lungs, brain and other organs. Health authorities continue to emphasize vaccination as the main method of preventing transmission.

The latest outbreak has also raised concerns about declining vaccination coverage. CDC data cited by Reuters show that average measles vaccination coverage among U.S. kindergarten children fell to about 92.5%, below the roughly 95% level commonly associated with maintaining community protection.

Public-health authorities are monitoring the outbreak closely as infections continue to appear in additional communities. The Pennsylvania situation demonstrates how quickly measles can spread when susceptible people are exposed to the virus.