Four people have died from measles in Pennsylvania, state health officials confirmed Tuesday, Sept. 15, WHYY News reported. The outbreak has now reached 693 cases across 38 counties.

The two newly reported deaths occurred in Jefferson County and Mifflin County. Both individuals were unvaccinated, according to the Pennsylvania Department of Health (DOH).

The Jefferson County death involved a 40-year-old woman who died Saturday, Sept. 12, from measles complications, according to a statement from Jefferson County Coroner Greg Furlong. The Mifflin County death involved an 18-year-old whose cause of death was acute disseminated encephalomyelitis (ADEM), a rare neurological complication of measles, according to 6abc Philadelphia.

Two earlier deaths, both infants in Lancaster County, were reported in August.

The last time the United States recorded four measles deaths in a single year was 1992, 6abc reported.

Bucks County has zero cases, but vaccination rates are slipping

Bucks County had no confirmed measles cases as of Sept. 15, according to Metro Philadelphia. Montgomery County had three. Lancaster County led the state with 296 confirmed cases.

Bucks County has no confirmed cases.

But local vaccination rates are trending in the wrong direction. MMR immunization rates among Bucks County students average 95.6%, down from 97.6% during the 2019–2020 school year, according to Central Bucks News. Medical experts classify 95% as the herd-immunity threshold needed to stop community transmission.

A Philadelphia Inquirer analysis found at least 12 Bucks County schools recorded kindergarten MMR rates below 90% in 2024, most of them faith-based private or charter schools.

Statewide, only about 93% of Pennsylvania kindergartners were fully vaccinated against measles during the 2025–2026 school year, according to state data reported by PhillyBurbs. Religious and philosophical exemptions among kindergartners rose from 2.4% in 2020–2021 to 5.4% five years later.

State response and what residents should do

Pennsylvania Secretary of Health Dr. Debra Bogen called the outbreak "the worst measles outbreak in more than three decades." In August, healthcare providers administered 46,000 MMR vaccine doses statewide, nearly double the typical 25,000 per month, according to the Philadelphia Inquirer.

Dr. Michael Cirigliano of Penn Medicine told FOX 29 on Sept. 15: "In Pennsylvania we are seeing this cluster of people who are not vaccinated and it can spread like wildfire."

Nearly 20% of Pennsylvanians identified with measles have been hospitalized, according to the DOH.

The Bucks County Health Department recommends residents confirm their child's MMR vaccine is up to date and keep vaccination records available, according to guidance reported by Central Bucks News on Sept. 9. Students with vaccine exemptions may be excluded from school during an active outbreak under state health rules, the outlet reported.

Residents who believe they were exposed or are experiencing symptoms can call the DOH hotline at 877-PA-HEALTH (877-724-3258).