Abstract
Background Weeks after issuing social distancing orders, all U.S. states and the District of Columbia at least partially relaxed these measures. Critical unanswered questions remain about the timing of relaxation, and if and how unregulated social distancing measures can be sustained while effectively maintaining epidemic control.
Methods We identified all statewide social distancing measures that were implemented and/or relaxed in the U.S. between March 10-July 15, 2020, triangulating data from state government and third-party sources. Using segmented linear regression, we evaluated the extent to which social distancing measure relaxation affected epidemic control, as indicated by the time-varying, state-specific effective reproduction number (Rt).
Results In the eight weeks prior to relaxation, mean Rt declined by 0.012 units per day (95% CI, -0.013 to -0.012), and 46/51 jurisdictions achieved Rt < 1.0 by the date of relaxation. After relaxation of social distancing, Rt reversed course and began increasing by 0.007 units per day (95% CI, 0.006-0.007), reaching a mean Rt of 1.16 eight weeks later, with only 9/51 jurisdictions maintaining Rt <1.0. Indicators often used to motivate relaxation at the time of relaxation (e.g. test positivity rate <5%) predicted greater post-relaxation epidemic growth.
Conclusions We detected an immediate and significant reversal in epidemic growth gains after relaxation of social distancing measures across the U.S. These results illustrate the potential pitfalls of premature relaxation of social distancing measures in the U.S.
Competing Interest Statement
The authors have declared no competing interest.
Funding Statement
Sir Henry Dale Fellowship, Wellcome Trust (UK); Sullivan Family Foundation
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This ecological analysis was based on publicly available data and was exempt from ethical review.
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Paper in collection COVID-19 SARS-CoV-2 preprints from medRxiv and bioRxiv
The Chan Zuckerberg Initiative, Cold Spring Harbor Laboratory, the Sergey Brin Family Foundation, California Institute of Technology, Centre National de la Recherche Scientifique, Fred Hutchinson Cancer Center, Imperial College London, Massachusetts Institute of Technology, Stanford University, University of Washington, and Vrije Universiteit Amsterdam.
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