 We sequenced 54 respiratory syncytial virus, RSV, genomes collected during 2021-22 and 2022-23 outbreaks in Washington, USA, to determine the origin of increased RSV cases. Detected RSV strains have been spreading for greater than 10 years, suggesting a role for diminished population immunity from low RSV exposure during the COVID-19 pandemic. This article was authored by Stephanie Goya, JD Sariewit, Daniel Falmer, and others.