Tejal Somvanshi
Pennsylvania’s measles outbreak reached 835 confirmed cases across 39 counties as of September 23, 2026 — a jump of 43 cases in two days. The state’s Department of Health is reporting 164 hospitalizations and four deaths linked to the outbreak.
Lancaster County remains the hardest-hit area with 342 confirmed cases. The outbreak started earlier this year and has spread from an initial cluster in Lancaster County outward into suburban and public-facility settings across the state. Confirmed cases span 39 of Pennsylvania’s 67 counties. The state’s death count is higher than what the CDC is currently reporting federally; CDC is using a definition still under revision, and its figures draw on different data timelines.
If you or your children are not fully up to date on MMR vaccination and live in Pennsylvania or nearby counties, this outbreak is no longer a background news event. Unvaccinated people exposed to confirmed cases are subject to public health guidance that includes exclusion from schools and workplaces for up to 21 days. Two MMR doses are 97% effective against measles. Additional clinics have been scheduled across the state for catch-up vaccinations.
What the Numbers Show
The trajectory of this outbreak shows consistent acceleration. Cases stood at 693 on September 14, rose to 731 on September 16, 767 on September 18, and 792 on September 21 before reaching 835 on September 23. That pace — roughly 20 to 40 additional confirmed cases every two days — reflects sustained community transmission.
More than 38,000 MMR doses were administered in the first three weeks of September alone, compared to approximately 25,000 in a typical full month. That surge shows substantially higher vaccination activity during the outbreak. Initial coverage of this outbreak focused on rural clusters with low vaccination rates; the current spread into suburban public facilities reflects coverage gaps in certain communities affecting those who cannot be vaccinated — newborns, immunocompromised people, and pregnant individuals.
What to do if exposed to measles in Pennsylvania: If you are unvaccinated and have been exposed, MMR given within 72 hours of exposure can prevent or reduce the severity of illness. Immune globulin given within six days of exposure is an option for those who cannot receive the vaccine. Anyone potentially exposed should monitor for fever, cough, runny nose, and rash, and follow individualized guidance from their local health department. Check the full CDC vaccine schedule for catch-up MMR timing. See our guide to identifying childhood rashes and fever symptoms.
Pennsylvania’s Department of Health is updating case counts regularly. Additional clinics are operating for catch-up vaccinations for unvaccinated or incompletely vaccinated residents.
