As the majority of states implemented stay-at-home orders in the early months of the coronavirus disease 2019 (COVID-19) pandemic, new research from Brown University has confirmed that those orders significantly slowed the spread of the disease for the entire country.

According to the study authors, COVID-19 has infected more than 18 million people across the globe and has hit the United States especially hard. Although just 4.2% of the global population is in the United States, the country accounted for approximately 33% of reported infections by the end of April.

“Understanding the trajectory of the epidemic in the US is critical and measuring the impact of stay-at-home orders on epidemic growth offers evidence for current and future COVID-19 control and containment measures,” said study lead co-author Mark Lurie, MA, PhD, in a statement. “While this was not a randomized trial, and therefore we cannot establish causation, what was clear in our study is that stay-at-home orders were significantly associated with slowing epidemic growth rates.”

Investigators calculated the pandemic’s doubling time on both a national level and for individual states. According to the study, an increase in doubling time indicates a slowing in the pandemic.

The authors found that between March 4 and April 4, before the effects of widespread lockdowns became apparent, the national pandemic doubling time was 2.68 days. This time increased to an average of 15 days between April 5 and April 30, demonstrating that the number of cases doubled in less than 3 days before mitigation measures were implemented. After those measures, the number of cases took more than 2 weeks to double.

“We hope that these findings contribute to a growing body of evidence aimed at studying the full course of COVID-19 in America,” said study lead co-author Joe Silva, a PhD student, in a statement. “This study does not imply stay-at-home orders were the sole factor that drove the observed increase in epidemic doubling time, but the data may be representative of the impact of multiple public health measures.”

The authors added that they are aware that the pandemic is far from over in the United States, and further research will be necessary even after mitigation measures are no longer in place.

“Our study period included data through the end of April, and since then cases have increased beyond what was previously thought to be the peak of the pandemic within our borders,” Silva said. “During this time, states have also removed stay-at-home orders, and it will be just as important to study the potential impacts on disease spread after these measures were no longer in place.”

REFERENCE
Stay-at-home orders significantly associated with reduced spread of COVID-19, study finds [news release]. Brown University; August 12, 2020. https://www.brown.edu/news/2020-08-12/stay-home. Accessed August 19, 2020.