Quantifying the Impact of COVID-19 Nonpharmaceutical Interventions on Influenza Transmission in the United States

Background. Nonpharmaceutical interventions (NPIs) have been implemented to suppress transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Evidence indicates that NPIs against coronavirus disease 2019 (COVID-19) may also have effects on 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 United States and US Department of Health and Human Services regions after implementation of NPIs in 2020. We investigate long-term effect of NPIs on influenza incidence by projecting influenza transmission at the national scale over the next 5 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 United States during the first 10 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. Conclusions. Healthcare systems need to prepare for potential influenza patient surges and advocate vaccination and continued precautions.

Automated summary

The study found that NPIs implemented in 2020 had significant effects on reducing the incidence and transmission of seasonal influenza in the United States, with more than 60% reduction in certain influenza strains during the initial 10 weeks. The reduction in influenza transmission varied geographically, and the potential accumulation of susceptibility to influenza infection post-NPIs may lead to large outbreaks, whose scale could be impacted by the duration of intervention and immunity to influenza. Healthcare systems should prepare for potential surges in influenza patients and promote vaccination and ongoing precautions.