Estimating the impact of non-pharmaceutical interventions on COVID mortality using reductions in influenza mortality as an effect indicator.

This study uses influenza mortality reduction (IMR) as an indicator of the aggregate effect of non-pharmaceutical interventions (NPI's) on the spread of respiratory infections to assess their impact on COVID mortality. Age-adjusted COVID mortality for US states were modeled using four variables: COVID mortality prior to introduction of NPI's, vaccination rates, IMR relative to 2016-2019, and population density. A simple linear model of the entire pandemic with only these variables explained 66% of the variability in COVID mortality with IMRs affecting the first two years and vaccination having an impact in the second and third year. A counterfactual model of no NPI's suggests they prevented 850,000 COVID related deaths in the United States. These results support the use of IMR's as an indicator of the aggregate impact of NPIs for controlling transmission of respiratory infections, including COVID and suggest that COVID mortality would have been almost 75% higher without them.