Assessing the interactions between COVID-19 and influenza in the United States

Casey M Zipfel; Shweta Bansal

Influenza dynamics are often evaluated through measuring influenza-like illness (ILI), which tracks cases of individuals with symptoms consistent with influenza, but where influenza is not laboratory confirmed. Typical ILI dynamics in an influenza season exhibit a small pre-holiday peak, followed by a larger post-holiday peak [7] . Recent ILI data for the United States show a markedly lower epidemic peak for the 2019-2020 influenza season compared to what would be expected based on the pre-holiday peak [8] . A similar phenomenon has been observed in other locations including Hong Kong and France [9, 10] . Understanding this uncharacteristic ILI behavior is important for understanding influenza epidemiology and optimizing influenza mitigation e↵orts. Assessing ILI dynamics in the US in the time of COVID-19 also provides a useful tool to understanding the ecological interaction between these two respiratory infections which share transmission pathways and interventions, as well as to gain a better understanding of COVID-19 dynamics and control.