Stay-home orders likely slowed COVID-19 spread, study finds

May 27, 2020

After 42 U.S. states and Washington, DC, issued stay-at-home orders in response to the rising death toll of the COVID-19 pandemic, the overall community infection rate declined by about 58 percent, according to a new study in the American Journal of Infection Control.

The researchers, from Johns Hopkins Bloomberg School of Public Health in Baltimore, used state government websites and case counts from the Johns Hopkins Center for Health Security to model the effects of mandatory social isolation on virus mitigation. They found that the community infection rate dropped from 12 percent more cases each day (indicating that cases were doubling every five or six days) to 5 percent (indicating that cases were doubling every 14 days) after the states locked down from March 19 to April 7.

The logged infection rate—a measure of the slope of the curve and of how fast cases are increasing—declined from 0.113 per day (95 percent confidence interval [CI], 0.110 to 0.115) to 0.047 (95 percent CI, 0.045 to 0.048) per day. The results were consistent across states. A sensitivity analysis to determine whether the rate of infection would have differed if orders were issued before or after April 1 found little difference.

Stay-at-home orders were defined as state-level orders that resulted in closure of nonessential businesses and furloughing of most government and commercial employees, prohibited large public events and gatherings, and disallowed travel unless it was for necessities such as food and healthcare. The eight states that have not issued such orders were excluded from the study.

The authors caution that their study had several limitations, the most important of which is that the evolving availability and use of coronavirus testing could have either increased or decreased the infection rates. They noted that testing was very limited in the early stages of the pandemic in the United States and gradually improved during March. While stay-at-home orders have stirred controversy because of their human and economic costs, the authors said that their results confirm their effectiveness in limiting community transmission and suggested that they may have a significant role in "flattening the curve."

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