A year into America’s COVID-19 epidemic, masking up is still inconsistent and heavily politicized across the country. Now, a new School of Public Health study led by students adds to the evidence that masks are a powerful tool for preventing the spread of the coronavirus.
Available as a pre-print on medRxiv ahead of peer-reviewed publication, the study finds that, over the spring and summer of 2020, states with higher rates of masking up had lower rates of COVID the following month.
But states with the least mask adherence saw higher rates of COVID the following month, regardless of mask policies or demographic factors.
“In a nutshell, our study shows that masks work,” says study senior author Martha Werler, professor and chair of epidemiology.
“The higher proportion of mask wearing the better, but 75-percent population adherence appears to be the key threshold, based on our observation that all states with at least this level of mask wearing had lower COVID-19 rates and none in the ‘red zone,’” she says.
For the study, Werler led a team of SPH students in the Epidemiology COVID-19 Response Corps, where graduate and undergraduate student volunteers work with faculty members on projects evaluating and rounding up the latest and best research to answer the pressing questions being asked by policymakers, clinicians, and communities.
“We initially sought to explore the relationship between state-issued mask policies in relation to COVID-19 rates, but quickly realized that adherence to policies that require or recommend mask wearing would be important to consider as well,” Werler says, noting that, as the study found, simply having a mask policy doesn’t mean people will wear them.
The team used publicly-available data on self-reported mask adherence for all 50 states and D.C. for April through September, and on COVID-19 cases in May through October. They used the SPH-based COVID-19 US State Policy Database for policy and demographic information.
They categorized states as having a “high” case rate if they had more than 200 cases per 100,000 residents.
None of the states that hit at least 75-percent mask adherence (Arizona, Connecticut, Hawaii, Massachusetts, Michigan, New York, Rhode Island, and Vermont) reached a “high” COVID-19 rate at any point from May to October. These states averaged 109 cases per 100,000 population the month after reaching at least 75-percent adherence.
On the other hand, every state with less than 25-percent mask adherence had reached a “high” rate by October. These states averaged 250 cases per 100,000 population.
When it came to mask policies, states without mask policies were consistently more likely to have “high” case rates, with 11 out of the 15 states without a policy by September reporting “high” rates by October. Far fewer states with mask policies had “high” COVID rates, with more than half reaching “high” rates only in October (21 out of the 36 states that had policies by September). However, in their analysis the researchers found that this was a matter of states with more mask adherence being more likely to have mask policies: Policies themselves did not predict more mask wearing or lower case rates.
“Simply adopting policies is not enough,” says study co-author Nedghie Adrien, a doctoral student in epidemiology. “As we know from all of the work done in behavioral sciences, implementing lasting behavioral change to get people to wear masks would require policies as well as motivators (whether there is a focus on positive or punitive enforcements), continued efforts to increase social acceptance of masks, as well as consistent and concise messaging across all public health and governmental bodies.”
“This work shows that at the end of the day, an individual’s choice to wear a mask truly makes an impact on COVID rates. I believe policies that emphasize the importance of that science-based choice and recognize the effect of adherence will be more successful,” Fischer says.
“Our article also outlines our process, our sources, and our epidemiological approach to analyzing the data, making sure that our research is transparent and can be trusted.”
Learn more about the Epidemiology COVID-19 Response Corps here.