Sustained transmission in under-vaccinated U.S. communities, fueled by MMR coverage gaps below the 95% herd-immunity threshold, is driving elevated 2026 case counts. As of June 11, the CDC has confirmed 2,073 measles cases—already approaching the full-year 2025 total of 2,288—with 29 active outbreaks and most infections linked to domestic chains rather than imported index cases. Key factors include the large South Carolina outbreak exceeding 900 cases and similar clusters in Utah and other states, alongside global resurgence increasing importation risk. CDC weekly surveillance updates and state health department reports through year-end will determine final tallies, while any acceleration in vaccination uptake or new containment measures could moderate further growth.