Lockdown measures helped reduce the number of COVID-19 cases in countries around the world, a new study finds.
Moreover, earlier stay-in-place restrictions such as closing schools and workplaces were tied to a greater reduction in cases, according to British researchers.
The findings, published July 15 in the BMJ, were based on data from 149 countries and regions.
"These findings might support policy decisions as countries prepare to impose or lift physical distancing measures in current or future epidemic waves," study co-author Nazrul Islam said in a journal news release.
Islam is a research fellow and medical statistician at the University of Oxford.
He and his team compared new cases of COVID-19 before and up to 30 days after the introduction of physical-distancing measures, such as restricting large gatherings and closing schools, workplaces and public transit.
On average, such measures were implemented nine days after the first reported case of COVID-19.
However, some countries took longer to implement measures, including Thailand (58 days), Australia (51 days), Canada (46 days), and Sri Lanka and Britain (45 days). Finland and Malaysia issued orders after 42 days, while Cambodia, Sweden and the United States did so after 40 days.
Implementation of any physical distancing measure was associated with an overall 13% average reduction in COVID-19 incidence, the study found.
In combination, restrictions on mass gatherings and closures of schools and workplaces appeared to play a significant role in the reduction of COVID-19 cases.
But shutting down public transit when the other measures were in place wasn't associated with an additional decline in COVID-19 cases, likely because fewer people were using public transportation, according to the authors.
The study provides important early evidence for the effectiveness of lockdown measures in controlling the new coronavirus pandemic, Thomas May, of Washington State University, wrote in an accompanying editorial.
However, the study can't prove a direct cause-and-effect relationship. And, May said, the findings need to be interpreted with caution due to shortfalls in testing practices and data collection in many countries.
"We must be careful not to mislead or overplay politically convenient findings and risk violating the public trust necessary for an effective pandemic response," May wrote.
The U.S. Centers for Disease Control and Prevention has more on COVID-19.
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