U.S. public-health researchers report that measles has been continuously circulating nationwide for more than a year, with 1,300 confirmed infections already in 2026 and outbreaks spanning multiple states. The resurgence began with a protracted Texas outbreak in early 2025 and expanded to clusters on the Utah–Arizona border and in South Carolina. Brown University’s Pandemic Center and other public-health authorities link the return to falling MMR vaccination rates below the 95% herd-immunity threshold, and warn the U.S. may lose its historic elimination status. Health officials and the Pan American Health Organization are monitoring spread across states; 30 states reported cases in 2026 and 47 since 2025 began. Measles’ high transmissibility makes local pockets of undervaccination particularly risky—epidemiologists emphasize that even modest declines in coverage can sustain widespread transmission. The development raises operational concerns for outbreak preparedness and routine immunization programs in clinical and public-health settings. Note: Measles is highly contagious and requires >95% population immunity to interrupt sustained transmission.