Pennsylvania reported 83 confirmed measles cases as of June 25, including 40 in Lancaster County and 20 in Lebanon County, with the outbreak concentrated in the Lancaster-Lebanon region since late April.
Many of the cases have been among unvaccinated residents, prompting officials to stress that two MMR doses provide 97% protection and that 1 in 5 infected children under 5 may require hospitalization.
More than 430 residents have been vaccinated at regional pop-up clinics over the past two months, while the state's 59 health centers have administered over 1,300 MMR doses this year.
Officials said overall risk remains low because nearly 94% of Pennsylvania kindergarteners had received two MMR doses in the 2024-25 school year, though online anti-vaccination messaging has complicated outreach.
The state warning comes as the CDC says 2026 is on track for the highest U.S. measles total since elimination, with 2,030 confirmed cases nationwide as of June 4.