Measles infections in the Americas have reached 10,139 so far this year, a 34-fold increase from the same point in 2024, the Pan American Health Organization said. The virus has caused 18 deaths and spread to 10 countries, marking the region’s largest resurgence since it interrupted endemic transmission in 2016. Canada accounts for the highest share of cases with 4,548, followed by Mexico with 3,911 and the United States with 1,356. PAHO data show fatalities concentrated in Mexico (14), the United States (3) and Canada (1). Paraguay recently became the tenth country to confirm circulation. PAHO attributes the surge to falling immunization rates: only 89 percent of children received a first measles–mumps–rubella dose in 2024 and 79 percent received the second, both below the 95 percent threshold needed for herd protection. About 89 percent of patients were unvaccinated or had unknown vaccination status. Genetic sequencing has identified two measles lineages; one is driving outbreaks in Mennonite communities across eight nations, while another is circulating in parts of Brazil. Local health authorities are also reporting community transmission outside known clusters, including a newly detected case in Colorado’s Mesa County with no travel link, underscoring PAHO’s call for immediate catch-up vaccination and enhanced surveillance.