BACKGROUND: Nonpharmaceutical interventions (NPIs) have been implemented to suppress the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Evidence indicates that NPIs against COVID-19 may also have effects on the transmission of seasonal influenza. METHODS: In this study, we use an absolute humidity-driven susceptible-infectious-recovered-susceptible (SIRS) model to quantify the reduction of influenza incidence and transmission in the US and HHS (the US Department of Health and Human Services) regions after implementation of NPIs in 2020. We investigate the long-term effect of NPIs on influenza incidence by projecting influenza transmission at the national scale over the next five years, using the SIRS model. RESULTS: We estimate that incidence of influenza A/H1 and B, which circulated in early 2020, was reduced by more than 60% in the US during the first ten weeks following implementation of NPIs. The reduction of influenza transmission exhibits clear geographical variation. After the control measures are relaxed, potential accumulation of susceptibility to influenza infection may lead to a large outbreak, the scale of which may be affected by length of the intervention period and duration of immunity to influenza. DISCUSSION: Healthcare systems need to prepare for potential influenza patient surges and advocate vaccination and continued precautions.
Quantifying the impact of COVID-19 non-pharmaceutical interventions on influenza transmission in the United States