Pennsylvania has surpassed 1,000 confirmed measles cases in 2026, recording five measles-associated deaths in the largest state outbreak in over three decades. The surge, driven largely by unvaccinated populations in counties like Lancaster and Mifflin, has intensified public health warnings and friction between state and federal officials over mortality data.
State health officials announced that confirmed cases reached 1,004 across the commonwealth as case counts climbed past the grim benchmark. The outbreak, which began in late April west of Philadelphia in the Lancaster-Lebanon region, marks the worst single-year tally in the United States since 1991, with national infections approaching 3,900 across 47 jurisdictions.
Lancaster and Mifflin Counties Bear the Heaviest Toll
Transmission remains heavily concentrated in specific regions. Lancaster County leads the commonwealth with 391 confirmed infections, followed by Mifflin County with 118 cases and Chester County with 84, according to the Pennsylvania Department of Health dashboard. Health officials report that more than 99% of all confirmed cases occurred in individuals who were not fully vaccinated against the virus.
While Allegheny County has recorded no confirmed residential cases, patients at UPMC Children’s Hospital faced multiple exposures in August after out-of-county visitors carrying the infection visited the emergency department. Community transmission has now been verified across 12 counties, including Centre, Chester, Clarion, Clearfield, Indiana, Jefferson, Lancaster, Mifflin, Snyder, Somerset, Union, and York.
Across the state, 198 patients have been admitted to the hospital since the start of the outbreak. The 22 new hospitalizations mark an increase of around 10% in under a week, according to data.
Five Fatalities and a Dispute Over Counting Criteria
Pennsylvania has recorded five measles-associated deaths this year, accounting for all measles-related fatalities nationwide in 2026. The state’s fifth death was confirmed in an unvaccinated Lancaster County resident, following earlier deaths that included two infants in Lancaster County, an 18-year-old in Mifflin County who suffered from acute disseminated encephalomyelitis, and a 40-year-old woman in Jefferson County.
Working alongside the Mifflin and Jefferson County coroners’ offices, the health department carried out thorough reviews to ascertain the cause of death; these efforts involved clinical evidence pointing directly to measles rather than a separate condition, alongside a positive lab result confirming the virus. The review process also factored in relevant medical histories and evaluated whether the deceased individuals had recent exposure to measles prior to passing away.
The mortality figures have sparked open disagreement between state leaders and federal health authorities. Health Secretary Robert F. Kennedy Jr. clashed over how the deaths are classified, with the Centers for Disease Control and Prevention initially omitting Pennsylvania’s early deaths from its weekly updates before gradually adding two fatalities to its national tally.
Clinics Administer Thousands of MMR Vaccine Doses
To combat the spread, state health centers and pop-up clinics have administered thousands of doses of the measles, mumps, and rubella vaccine. State health officials noted that routine vaccination providers administered more than 49,000 MMR doses in August alone, far outpacing the typical monthly average of about 25,000. Nearly 4,000 doses have been administered at pop-up clinics in affected Pennsylvania communities.
With domestic measles elimination status under review by international health officials in November, physicians across the country are bracing for potential winter spikes as unvaccinated children return to classrooms.