A national mask mandate in the U.S. early in the coronavirus pandemic could have reduced the weekly growth rate of cases and deaths by more than 10 percentage points in late April and saved up to 47,000 lives by the end of May, according to recent research.

In a study published in the January 2021 issue of the Journal of Econometrics, three economists, using a causal model simulation, estimated that requiring employees in public businesses to wear face masks starting on March 14, the day after President Donald Trump declared a national emergency, could have led to 21% fewer cumulative cases and 34% fewer deaths at the end of May, saving between 19,000 and 47,000 lives. 

On May 31, the World Health Organization reported 1.72 million COVID-19 cases in the U.S. and 101,567 deaths.

The researchers also noted that without stay-at-home orders, the number of coronavirus cases would have been between 6% and 63% larger by the end of May, and without business closures, cases would have been between 17% and 78% larger.

The range of potential lives saved is wide, co-author Hiroyuki Kasahara of the Vancouver School of Economics said, because of the properties of exponential growth — economists estimate that masks would have reduced the weekly growth rate by between 5 and 15 percentage points, which, after eight weeks, can lead to vastly different totals.

“It’s like a compounding interest type of argument,” Kasahara said. “So if you borrow money, the interest rate is 20% for the credit card, that’s going to be a nightmare after two or three years. … And a similar thing happened here. So say instead of 20%, it’s 10%, the eventual amount of debt you’re going to have is going to be very different.”

Mask mandates reduce case and death growth even when behavior is constant, the researchers said, meaning that masks may reduce infections with relatively little economic impact.

The authors said their study “is observational and should be interpreted with great caution,” but added that their empirical analysis “robustly indicates” that mandating face masks has reduced the spread of COVID-19 without affecting people’s social distancing behavior.

Additionally, the Institute for Health Metrics and Evaluation at the University of Washington projected in early August that if 95% of people in the U.S. were to immediately start wearing masks, 66,000 lives would be saved by December, which is largely consistent with Kasahara’s results.

“Mandatory masks is like no drinking and driving,” Kasahara said. “The reason why there’s no drinking and driving is not about you not having an accident — it’s about not hitting somebody. And it’s the same thing [here]. … It’s about others.”

Kasahara and his co-authors were interested in studying the effectiveness of mask mandates, he said, because at the end of March, when their research began, not many people were talking about or advocating for the use of masks. 

This particular topic was difficult to study, Kasahara said, because the economists were not able to do randomized controlled trial experiments, “so that gold standard is not going to be there.”

Conducting research was additionally complicated by the pandemic, he added, because of time constraints and working conditions.

“Everybody was locked down — including myself. I was locked out of the office,” Kasahara said. “So I had to be at home with my kids — I have three kids — and my wife was not so happy with just focusing on this research. To be honest, it was one of the toughest times in my academic career.”

Kasahara and his colleagues are currently working on a follow-up study on how school and college closures have impacted the coronavirus infection and death rates. They initially attempted to examine school closures in this study, but the results were uncertain.

“Many of the lockdown policies are state-level policies, however the school choices, in terms of going for remote and open, are district-level choices,” Kasahara said. “So within a state, there’s a lot of differences in terms of the mode of learning when they open up and the timing of the opening up.”

So far, he said, there seems to be a “strong association” between school and college openings.

“I’m a parent of three kids, and I’m always going to say, ‘Don’t close the school,’ even now,” Kasahara said. “But being aware of the possibility of transmission within school settings … that’s very important.”

The study “Causal impact of masks, policies, behavior on early covid-19 pandemic in the U.S.,” published online on Oct. 17, 2020 and in the January issue of the Journal of Econometrics, was authored by Victor Chernozhukov, Massachusetts Institute of Technology; Hiroyuki Kasahara, Vancouver School of Economics; and Paul Schrimpf, Vancouver School of Economics.