Social Distancing Causally Impacts the Spread of SARS-CoV-2: A U.S. Nationwide Event Study

Objectives To assess the causal impact of a spontaneous relaxation of social distancing on the spread of SARS-CoV-2 in the United States (U.S.), while controlling for social mobility and state-imposed social distancing restrictions. Design Event study. Setting Quasi-experimental setting created by the U.S. nationwide protests precipitated by George Floyd’s tragic death on May 25, 2020. Population Individuals in 3,142 U.S. counties from all 50 states and the District of Columbia. Main Outcome Measures The number of daily confirmed COVID-19 cases in all U.S. counties between the period of January 22, 2020, and June 20, 2020, and the cumulative change in COVID-19 cases in protest counties relative to non-protest counties following the onset of the protests. Results We document a country-wide increase of over 3·06 cases per day, per 100,000 population, following the onset of the protests (95%CI: 2·47–3·65), and a further increase of 1·73 cases per day, per 100,000 population, in the counties in which the protests took place (95%CI: 0·59–2·87). Relative to the week preceding the onset of the protests, this represents a 61·2% country-wide increase in COVID-19 cases, and a further 34·6% increase in the protest counties. Conclusions Our study documents a significant increase in COVID-19 case counts in counties that experienced a protest, and we conclude that social distancing practices causally impact the spread of SARS-CoV-2. The observed effect cannot be explained by changes in social distancing restrictions and social mobility, and placebo tests rule out the possibility that this finding is attributable to chance. Our research informs policy makers and provides insights regarding the usefulness of social distancing as an intervention to minimize the spread of SARS-CoV-2.