Domestic Measles Importations in Washington State, January 2026

AbstractMeasles outbreaks are increasing in frequency and size in the United States. Within 2 weeks, there were five distinct out-of-state measles importations into Washington State epidemiologically connected to an outbreak in South Carolina, resulting in a total of 26 measles cases during January-February 2026. Genomic analyses supported epidemiologic conclusions regarding exposure sources of imported cases and independence among importations. Adherence to isolation and quarantine likely limited onward transmission in undervaccinated communities. Combining timely genomic data analysis with epidemiologic information can strengthen understanding of measles outbreaks as public health jurisdictions prepare to respond to increases in imported measles cases.