Pennsylvania's measles outbreak has topped 1,000 cases, the worst in the US since the disease was wiped out domestically in 2000.
State health officials counted 1,078 cases for 2026 as of Tuesday afternoon. Twelve were isolated infections from January and March; the other 1,066 trace to a single outbreak that began in April. The past week alone added 145 cases, including 74 reported since Monday's update - 40 of which were infections identified more than two weeks ago and only now logged. Hospitals have treated 207 patients, and five people have died.
This is the largest measles outbreak the country has recorded since 1991, and it's happening in a disease the US declared eliminated a quarter-century ago. Every death has been in someone unvaccinated, including two infants too young to get the shot - a reminder that herd immunity protects the people who have no choice in the matter.
Measles doesn't spread this fast in a well-vaccinated population; it spreads this fast when vaccination rates slip below the threshold that keeps it contained.