Estimating The Impact of Public Health Interventions on COVID Mortality in The United States Using Reductions in Influenza Mortality as an Indicator Of Non-Pharmaceutical Infection Control

Background

Non-pharmaceutical interventions (NPIs) for control of COVID include a range of methods from masks to closures of schools and businesses with the efficacy of any individual strategy contingent on which other NPIs are employed and the extent of compliance with those strategies. In the case of a public health intervention, one typically looks at historical data for comparison, but, because COVID is a new disease, we have no such data. However, we do have extensive historical data for influenza, a respiratory disease with similar modes of transmission. Influenza incidence and mortality dropped dramatically during the COVID pandemic, almost certainly because of these NPIs. The extent of that drop provides an indirect measure of the efficacy of COVID NPIs in stopping the transmission of respiratory infections.

This study evaluates the association of influenza mortality reduction (IMR) during the pandemic with age-adjusted COVID mortality among US states, adjusting for mortality prior to the introduction of NPIs and vaccination rates, while taking into account the impact of population density on NPI effectiveness.

Results

A simple linear model with pre-intervention COVID mortality, IMR, vaccination rate, and population density explained 70% of the state-to-state variability in age adjusted COVID mortality. The resulting model suggests that NPIs prevented 831,000 COVID related deaths in the United States over the course of the pandemic.

Conclusions

These results provide strong evidence that IMR is an accurate indicator of the efficacy of NPIs in controlling transmission of respiratory infections, including COVID. This analysis suggests that NPIs together with vaccination prevented an estimated 2.15 million COVID related deaths and full intervention could have prevented over 700,000 more.