Masks reduce the spread of COVID-19. But just how much of an effect do they have?
In a new study, researchers found that if the U.S. had introduced a uniform national mask mandate for employees of public-facing businesses on April 1, the number of deaths in the U.S. would likely have been 40% lower on June 1.
They found it is a very effective policy that includes relatively little economic disruption. It produced a considerable reduction in fatalities.
Among other findings of the ongoing pandemic, drawing on the timing of state policy announcements, medical data, and Google mobility data, the study also shows that in the same timeframe, total COVID-19 cases in the U.S. would have likely been 80% higher without the stay-at-home orders implemented by the vast majority of states.
Additionally, the researchers evaluated how much the reduction in people’s movement—such as commuting and shopping trips—has followed specific state policies, and how much has stemmed from personal decisions to stay home more often.
Their conclusion is that each factor accounts for about half of the decline in physical movement during the pandemic.
The research was conducted by a team at MIT and elsewhere.
To conduct the study, the team took advantage of the fact that many U.S. states have implemented mask mandates at different times this year.
By examining the before-and-after trajectories of cases and deaths, the study was able to identify the impact of the mask mandates.
To be sure, states also differ from each other in numerous ways that may influence the spread of COVID-19, including demographic factors such as the age and health of state residents; population density; additional state-level policies curbing the spread of COVID-19; and self-directed changes in population movement, in response to the pandemic.
The study also accounted for the fact that COVID-19 testing increased during this time.
The team found the results hold up. Controlling for behavior, information variables, confounding factors—the mask mandates are critical to the decline in deaths. No matter how they look at the data, that result is there.
Specifically, after accounting for those circumstances, the researchers estimated that mask mandates would have produced a 40% reduction in deaths, nationally.
The team also found an 80% reduction due to stay-at-home orders.
Given that many states have continued changing their policies after June 1, with significant variation in state-level mask policies and economic reopening plans, the scholars say they are continuing to study the topic, and plan to release more findings of it in the near future.
One author of the study is Victor Chernozhukov, a professor in the Department of Economics and the Statistics and Data Science Center at MIT.
The study is posted on the MedRxiv preprint server and as part of the COVID Economics paper series.
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