Public Compliance With Social Distancing Measures and SARS-CoV-2 Spread : A Quantitative Analysis of 5 States

Abstract

Objective: We quantified the association between public compliance with social distancing measures and the spread of SARS-CoV-2 during the first wave of the epidemic (March-May 2020) in 5 states that accounted for half of the total number of COVID-19 cases in the United States.

Methods: We used data on mobility and number of COVID-19 cases to longitudinally estimate associations between public compliance, as measured by human mobility, and the daily reproduction number and daily growth rate during the first wave of the COVID-19 epidemic in California, Illinois, Massachusetts, New Jersey, and New York.

Results: The 5 states mandated social distancing directives during March 19-24, 2020, and public compliance with mandates started to decrease in mid-April 2020. As of May 31, 2020, the daily reproduction number decreased from 2.41-5.21 to 0.72-1.19, and the daily growth rate decreased from 0.22-0.77 to -0.04 to 0.05 in the 5 states. The level of public compliance, as measured by the social distancing index (SDI) and daily encounter-density change, was high at the early stage of implementation but decreased in the 5 states. The SDI was negatively associated with the daily reproduction number (regression coefficients range, -0.04 to -0.01) and the daily growth rate (from -0.009 to -0.01). The daily encounter-density change was positively associated with the daily reproduction number (regression coefficients range, 0.24 to 1.02) and the daily growth rate (from 0.05 to 0.26).

Conclusions: Social distancing is an effective strategy to reduce the incidence of COVID-19 and illustrates the role of public compliance with social distancing measures to achieve public health benefits.

Keywords: COVID-19; SARS-CoV-2; impact assessment; public compliance; social distancing.

Figure

Seven-day moving average trends of the daily reproduction number, daily growth rate, daily encounter-density change, and social distancing index (SDI) in New York during the COVID-19 epidemic, March–May 2020. The stay-at-home directive began on March 21, 2020. A 10-day lag was incorporated in the trend analysis of the COVID-19 spread and human mobility. The SDI uses mobile device location data from multiple sources (ie, population census data and location data from cell phones and vehicles) to discriminate between person movement and vehicle movement. The SDI score ranges from 0 to 100 and measures the extent to which area residents and visitors practice social distancing. A value of 0 indicates no social distancing, and 100 indicates perfect social distancing. The daily encounter-density change measures the percentage change in the number of encounters compared with the pre-epidemic national baseline. A potential human encounter is defined by the space between 2 mobile phones (≤50 m) and time (≤60 minutes). A daily encounter-density change >0 indicates that human mobility is greater than the pre-epidemic national baseline, whereas values <0 suggest that mobility activity is less than the national baseline. A value of 0 indicates that mobility is the same as the national baseline.