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Social distancing to slow the U.S. COVID-19 epidemic: an interrupted time-series analysis

Our take —

Statewide social distancing measures in the United States have been effective at reducing the daily growth rate of COVID-19, but further analyses are needed to understand which measures were most effective.

Study design

Ecological

Study population and setting

Using publicly available data on the number of COVID-19 cases by state in the United States of America, the authors used an interrupted time series analysis to determine the impact of social distancing implementation on the daily growth rate of COVID-19 cases in each state. Interrupted time series analysis uses regression modeling to estimate a pre- and post-intervention slope (rate) , and the change between them at the point at which a defined intervention is put in place.

Summary of Main Findings

Statewide social distancing measures led to a reduction in mean daily growth of COVID-19 cases. At the state level, there was an average reduction in the daily growth rate of 0.8% [95% CI -1.4% to -0.2%] four days after implementation of the first social distancing measures.

Study Strengths

The study takes advantage of different implementation dates for state-wide social distancing.

Limitations

Implementation of statewide social distancing may have been in response to increasing COVID-19 cases. Given that each state implemented statewide social distancing measures differently, it is unclear which social distancing measures were the most effective. The results do not account for any concurrent increases in testing and surveillance, potential variations in compliance, and differences between states in terms of socioeconomic and health status.

Value added

The study demonstrates in a straightforward manner the benefit of statewide social distancing measures in the United States.