**Sustained community transmission from multiple active outbreaks, concentrated in unvaccinated populations, continues to drive rapid case growth in 2026.** As of September 17, the CDC reports 3,471 confirmed U.S. measles cases this year across 47 jurisdictions—already far exceeding the full-year 2025 total of 2,289—with 95% outbreak-associated and 9% hospitalized. Pennsylvania leads recent increases (hundreds of new cases in recent weeks), followed by persistent activity in states like South Carolina and Utah. Low MMR vaccination coverage, especially among school-age children, sustains chains of transmission for this highly contagious airborne virus. CDC weekly updates, expected imminently, and any additional state reports before September 30 could add triple-digit cases, while model consensus and surveillance timing introduce modest uncertainty in final tallies.