Five deaths and 198 hospitalisations: inside Pennsylvania's measles outbreak

Pennsylvania's health department confirmed 1,004 measles cases in 2026 as of early October, an increase of 106 cases in the past week. The cases span 39 of the state's 67 counties and represent nearly a quarter of all U.S. measles cases reported this year.

More than 99% of people with measles in Pennsylvania were unvaccinated. Just four cases occurred in vaccinated people.

The state has confirmed 198 hospitalizations, a rate of nearly 20%. Five people have died: two infants, a 20-year-old woman with leukemia who was undergoing chemotherapy, a 40-year-old woman with asthma and COPD, and an 18-year-old who developed disseminated encephalomyelitis. All were unvaccinated.

Nationwide, the CDC reported 3,887 confirmed measles cases as of October 2, across 47 jurisdictions, with 42 new outbreaks and 95% of cases outbreak-associated. No other state has reported more than 1,000 measles cases in 35 years, when New York City alone confirmed 2,000 cases in 1991.

The concentration of severe outcomes in unvaccinated people is consistent with what is known about the virus. Measles is the most contagious pathogen known: up to 9 of 10 unvaccinated people exposed will become infected, and each case can spread to 12 to 18 others. That transmission profile explains how an outbreak can move from a handful of cases to more than a thousand within a single state, and why hospitalizations and deaths cluster where vaccination coverage is lowest.

The figures describe an association between vaccination status and outcomes, not a controlled comparison.

The practical takeaway is narrow and well established. Two doses of measles-mumps-rubella vaccine are highly effective at preventing infection, and unvaccinated people exposed to measles face a high probability of infection. States with vaccination gaps similar to Pennsylvania's face the same transmission math.

- https://www.cidrap.umn.edu/measles/pennsylvania-confirms-more-1000-measles-cases - https://www.cdc.gov/measles/data-research/index.html - https://www.nfid.org/pennsylvania-measles-outbreak-3-lessons-for-the-us/