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

Abstract

Background: To date, no study has examined the effectiveness of social distancing, while controlling for social mobility and social distancing restrictions in the United States. We utilize the quasi-experimental setting created by the nationwide protests precipitated by George Floyd’s tragic death on May 25, 2020, to assess the causal impact of social distancing on the spread of SARS-CoV-2. Methods: Our sample period spans from January 22, 2020, to June 20, 2020, and consists of 474,422 county-days representing 3,142 counties from all 50 states and the District of Columbia. To assess the change in COVID-19 case counts following the protests, we employ a differences-in-differences estimation strategy in a multivariate setting, in which we control for social distancing restrictions and social mobility across counties. We also control for covariates that may influence SARS-CoV-2 transmission, and implement placebo tests using a Monte Carlo simulation. Findings: 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 the infection rate, and a further 34 · 6 % increase in the protest counties. Interpretation: 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. Funding: We acknowledge the financial support from the Smith School of Business Distinguished Faculty Fellowship at Queen’s University.Declaration of Interests: Authors declare no conflict of interest.