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. 2021 May;361(5):575-584.
doi: 10.1016/j.amjms.2021.01.007. Epub 2021 Jan 11.

Policy Interventions, Social Distancing, and SARS-CoV-2 Transmission in the United States: A Retrospective State-level Analysis

Nickolas Dreher  1 , Zachary Spiera  2 , Fiona M McAuley  2 , Lindsey Kuohn  2 , John R Durbin  2 , Naoum Fares Marayati  2 , Muhammad Ali  2 , Adam Y Li  2 , Theodore C Hannah  2 , Alex Gometz  3 , J T Kostman  4 , Tanvir F Choudhri  2
Affiliations

Policy Interventions, Social Distancing, and SARS-CoV-2 Transmission in the United States: A Retrospective State-level Analysis

Nickolas Dreher et al. Am J Med Sci. 2021 May.

Abstract

Background: Various non-pharmaceutical interventions (NPIs) such as stay-at-home orders and school closures have been employed to limit the spread of Coronavirus disease (COVID-19). This study measures the impact of social distancing policies on COVID-19 transmission in US states during the early outbreak phase to assess which policies were most effective.

Methods: To measure transmissibility, we analyze the average effective reproductive number (Rt) in each state the week following its 500th case and doubling time from 500 to 1000 cases. Linear and logistic regressions were performed to assess the impact of various NPIs while controlling for population density, GDP, and certain health metrics. This analysis was repeated for deaths with doubling time to 100 deaths with several healthcare infrastructure control variables.

Results: States with stay-at-home orders in place at the time of their 500th case were associated with lower average Rt the following week compared to states without them (p<0.001) and significantly less likely to have an Rt>1 (OR 0.07, 95% CI 0.01-0.37, p = 0.004). These states also experienced longer doubling time from 500 to 1000 cases (HR 0.35, 95% CI 0.17-0.72, p = 0.004). States in the highest quartile of average time spent at home were also slower to reach 1000 cases than those in the lowest quartile (HR 0.18, 95% CI 0.06-0.53, p = 0.002).

Conclusions: Stay-at-home orders had the largest effect of any policy analyzed. Multivariate analyses with cellphone tracking data suggest social distancing adherence drives these effects. States that plan to scale back such measures should carefully monitor transmission metrics.

Keywords: COVID-19; Coronavirus; Limitations on mass gatherings; Non-essential business closure; Non-pharmaceutical interventions; Novel coronavirus; Public policy; SARS-CoV-2; School closure; Social distancing; Stay-at-home order.

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Conflict of interest statement

Declaration of Competing Interest The authors of this manuscript have no conflicts of interest to disclose.

Figures

Fig 1
figure 1
Average Rt during the week following the 500th case by each U.S. state.
Fig 2
figure 2
Hazards curve demonstrating the probability of reaching 1000 cases separated by (A) states with and without a stay-at-home order prior to the 500th case, (B) the highest vs. lowest quartile of percent time spent at home based on Google mobility data for all states, and (C) the highest vs. lowest quartile of percent time spent at home amongst states that had a stay-at-home order prior to the 500th case.
Fig 3
figure 3
Hazard curve showing the probability of reaching 100 deaths separated by states with and without a stay-at-home (SAH) order prior to the 50th death.
Fig 4
figure 4
Time spent in residential areas before and after stay-at-home order.
See this image and copyright information in PMC

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