Influenza Mortality as an Indicator of the Efficacy of COVID-Related, Non-pharmaceutical Interventions to Reduce the Spread of Respiratory Infections

BackgroundNon-pharmaceutical interventions (NPIs) have been criticized as ineffective in preventing COVID. Because it is a new disease with NPIs introduced almost immediately, we have no way to evaluate the counterfactual of non-intervention easily and directly. We do, however, have historic data on influenza, a respiratory disease with similar patterns of transmission and a well-established CDC surveillance system in the US. These data provide us with an excellent way to indirectly evaluate the efficacy of these interventions. ResultsDuring the three seasons prior to COVID from 2016-17 to 2018-19, the mean total US influenza mortality was 9,917 deaths per season. During the pandemic, total influenza mortality declined by 80 percent relative to historical levels. Pediatric influenza morality decreased by 85 percent. At the state level, the average drop in mortality over the two flu seasons of the pandemic was strongly correlated with the percent of the 2020 presidential votes cast for Joe Biden (r2=0.39). ConclusionsThese data provide strong evidence that COVID NPIs dramatically reduced the spread of influenza. Given its similar routes of transmission, these results support the assertion that these NPIs also substantially reduced COVID transmission, morbidity, and mortality. The effectiveness of NPIs was highly correlated with the political leanings of each state, suggesting that politics influenced the effectiveness of and/or compliance with NPI strategies.