COVID-19 transmission in the U.S. before vs. after relaxation of statewide social distancing measures

Background Weeks after issuing social distancing orders to suppress severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission and reduce growth in cases of severe coronavirus disease 2019 (COVID-19), all U.S. states and the District of Columbia partially or fully relaxed these measures.

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 estimated the extent to which relaxation of social distancing affected epidemic control, as indicated by the time-varying, state-specific effective reproduction number (R t ).

Results In the eight weeks prior to relaxation, mean R t declined by 0.012 units per day (95% CI, -0.013 to -0.012), and 46/51 jurisdictions achieved R t < 1.0 by the date of relaxation. After relaxation of social distancing, R t reversed course and began increasing by 0.007 units per day (95% CI, 0.006-0.007), reaching a mean R t of 1.16 eight weeks later, with only 9/51 jurisdictions maintaining R t <1.0. Parallel models showed similar reversals in the growth of COVID-19 cases and deaths. Indicators often used to motivate relaxation at the time of relaxation (e.g. test positivity rate <5%) predicted greater post-relaxation epidemic growth.