Although most of these severe cases in the COVID-19 pandemic have been due to the Delta variant that has been dominant since May 2021, the recently identified Omicron variant is rapidly displacing Delta as the most common SARS-CoV-2 variant. While there is still much to be learned about the epidemiology of Omicron, available data suggest that this variant is substantially more transmissible than the Delta variant and is capable of significant immune evasion. In 2021 winter, the US may face a triple respiratory virus threat: Delta, Omicron, and seasonal influenza. To mitigate the effects, especially strain on health care resources, robust efforts are needed to increase vaccination against both influenza and COVID-19, including booster doses.