**Sustained multi-state outbreaks have driven 2026 U.S. measles cases to a record pace.** As of September 24, the CDC reported 3,659 confirmed cases across 47 jurisdictions, with 95% outbreak-associated and 40 new outbreaks this year—already far exceeding the 2019 post-elimination high of 1,274 and all of 2025’s 2,289 cases, with over three months remaining. Roughly 95% of cases involve unvaccinated individuals or those with unknown status; 9% have required hospitalization. The virus’s high contagiousness via airborne transmission sustains chains in under-vaccinated communities, particularly in Pennsylvania, South Carolina, and Utah. Weekly CDC updates on Thursdays provide the primary near-term data releases that can shift trader views on the final annual total, alongside any shifts in MMR coverage or outbreak containment.