**Sustained transmission in under-vaccinated communities is driving U.S. measles cases to record levels in 2026.** As of October 8, the CDC has confirmed 4,080 cases across 47 jurisdictions and Washington, D.C.—already exceeding the full-year 2025 total of 2,289 and marking the highest annual count since 1991. Roughly 96% of cases are outbreak-associated across 42 clusters, with Pennsylvania alone accounting for more than 1,100 infections and state-reported deaths exceeding the CDC’s provisional count of two. About 95% of patients are unvaccinated or have unknown status, while two-dose MMR vaccination confers 97% effectiveness. Weekly CDC updates continue to show 150–200 new cases, with ongoing activity in states such as South Carolina, Wisconsin, and Ohio; school-year surveillance and any expanded vaccination efforts will shape final totals through year-end.