Respiratory viruses, like flu (influenza), COVID-19, and RSV (respiratory syncytial virus) circulate year-round in the U.S and California—and are typically more active in fall and winter. CDPH encourages Californians to take simple actions to reduce the risk of catching and spreading respiratory viruses: Stay Up to Date on Vaccines, Stay Home if You’re Sick, Test and Treat, Consider Wearing a Mask, Wash Your Hands, Cover Your Cough or Sneeze, Improve Ventilation.