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Comparative Study
. 2020 Aug 11;17(8):e1003244.
doi: 10.1371/journal.pmed.1003244. eCollection 2020 Aug.

Social distancing to slow the US COVID-19 epidemic: Longitudinal pretest-posttest comparison group study

Mark J Siedner  1   2   3 , Guy Harling  3   4   5   6   7 , Zahra Reynolds  1 , Rebecca F Gilbert  1 , Sebastien Haneuse  8 , Atheendar S Venkataramani  9   10 , Alexander C Tsai  1   2   7
Affiliations
Comparative Study

Social distancing to slow the US COVID-19 epidemic: Longitudinal pretest-posttest comparison group study

Mark J Siedner et al. PLoS Med. .

Erratum in

Abstract

Background: Social distancing measures to address the US coronavirus disease 2019 (COVID-19) epidemic may have notable health and social impacts.

Methods and findings: We conducted a longitudinal pretest-posttest comparison group study to estimate the change in COVID-19 case growth before versus after implementation of statewide social distancing measures in the US. The primary exposure was time before (14 days prior to, and through 3 days after) versus after (beginning 4 days after, to up to 21 days after) implementation of the first statewide social distancing measures. Statewide restrictions on internal movement were examined as a secondary exposure. The primary outcome was the COVID-19 case growth rate. The secondary outcome was the COVID-19-attributed mortality growth rate. All states initiated social distancing measures between March 10 and March 25, 2020. The mean daily COVID-19 case growth rate decreased beginning 4 days after implementation of the first statewide social distancing measures, by 0.9% per day (95% CI -1.4% to -0.4%; P < 0.001). We did not observe a statistically significant difference in the mean daily case growth rate before versus after implementation of statewide restrictions on internal movement (0.1% per day; 95% CI -0.04% to 0.3%; P = 0.14), but there is substantial difficulty in disentangling the unique associations with statewide restrictions on internal movement from the unique associations with the first social distancing measures. Beginning 7 days after social distancing, the COVID-19-attributed mortality growth rate decreased by 2.0% per day (95% CI -3.0% to -0.9%; P < 0.001). Our analysis is susceptible to potential bias resulting from the aggregate nature of the ecological data, potential confounding by contemporaneous changes (e.g., increases in testing), and potential underestimation of social distancing due to spillover effects from neighboring states.

Conclusions: Statewide social distancing measures were associated with a decrease in the COVID-19 case growth rate that was statistically significant. Statewide social distancing measures were also associated with a decrease in the COVID-19-attributed mortality growth rate beginning 7 days after implementation, although this decrease was no longer statistically significant by 10 days.

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Conflict of interest statement

I have read the journal's policy and the authors of this manuscript have the following competing interests: GH reports having received funding within the past five years from the U.S. National Institutes of Health, the Wellcome Trust, the Royal Society, and the International Initiative for Impact Evaluation (3ie). ACT receives a stipend as a Specialty Consulting Editor for PLOS Medicine and serves on the journal's editorial board. All other authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Scatter plots and predictive margins with 95% confidence interval derived from regression models of the daily COVID-19 growth rate before versus after implementation of the first statewide social distancing measures and statewide restrictions on internal movement.
(A) First statewide social distancing measure. (B) Statewide restrictions on internal movement. The red line indicates the date of implementation in each state. The green dashed line is 4 days after implementation of the social distancing measure. COVID-19, coronavirus disease 2019.
See this image and copyright information in PMC

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