COVID-19 Cloth Masks: How Effective Are They?

Cloth face masks made by Denver artist Laura Shill.
Courtesy of Laura Shill
Cloth face masks made by Denver artist Laura Shill.
Amid the COVID-19 outbreak, national and local public health experts, as well as Governor Jared Polis and members of the White House task force addressing the virus, have encouraged people to wear cloth face masks whenever they leave home, including when they're outside.

But while mask-wearing buy-in has increased in many parts of Denver, resistance among millennials and residents of communities such as Castle Pines has been accompanied by debate about how effective such face coverings are at actually stopping infection.

The answer offered by a new report: Cloth masks definitely aren't an impenetrable shield, and by one measure, they only offer a 13 percent reduction in the odds of being infected by an asymptomatic virus carrier. But when combined with other tactics, their use can help prevent Colorado from a catastrophic rise in cases and casualties once the state's April 26 stay-at-home order is lifted.

These conclusions can be found in "Findings on the COVID-19 Epidemic in Colorado to Date and Projections for Future Scenarios of Social Distancing," a report from the state's COVID-19 modeling group that provided the data for our recent post about the risk of secondary infection waves as Colorado society reopens. The report was assembled by representatives from the Colorado School of Public Health, the University of Colorado School of Medicine, the University of Colorado Boulder Department of Applied Mathematics, the University of Colorado Denver and Colorado State University.

The analysis concludes that "mask wearing, improved case detection along with timely, effective case containment to prevent further spread of infections, and recommendations that high-risk populations maintain high levels of social distancing will further delay the next peak and reduce the hospital demand at the peak." Modeling shows that the wearing of masks by members of the public is part of a formula that can lead to better outcomes.

Still, the report draws a distinction between cloth face masks and the so-called N95 widely used in health-care settings. Furthermore, the analysis of the benefits of homemade masks is based on hypotheses and a slew of variables, as opposed to undisputed fact.

"Masks worn by the public can be protective of others by reducing exposure to the droplets propelled into the air by coughing and sneezing," one passage reads. "Masks worn by health care professionals and others at high risk are also intended to protect against inhalation of the virus; N95 masks are needed for this purpose as they block inhalation of small infectious particles. There is still uncertainty as to whether the virus is present in both the larger particles (referred to as droplets) and the smaller particles (referred to as aerosols). Masks that would be generally worn by the public are effective to varying degrees (depending on materials and patterns of use) in reducing exposure to droplets."

Another positive in regard to masks: They can protect wearers from themselves. "Beyond the physical barrier that masks provide, they may also alter behavior by keeping wearers from touching their faces, and they shift cultural norms around avoiding contact with others," another section states.

Users shouldn't assume that wearing a cloth mask makes them immune, though. "Some have proposed that using masks may lead to a misconception that wearers are protected against infection," the report acknowledges. "Overall, we view use of masks as a 'no regrets' addition to the strategies that can be used to reduce the spread of infection." Yet "the effectiveness of masks depends on how many people use them and how well they work in actuality."

Quantifying the positive attributes of masks remains difficult. The modeling group cites multiple studies "suggesting the use of cloth face masks by the public can reduce transmission by asymptomatic and pre-symptomatic individuals," but "the effectiveness of mask wearing depends on both the ability of the mask to trap viral particles and the proportion of the population wearing masks appropriately."

In the report, the researchers say they "assume masks made from basic household materials are approximately 50 percent effective at trapping viral particles shed by infectious individuals," and that half of the populace is currently wearing them. However, they warn that "there remains considerable uncertainty about both of these assumptions. Given that approximately one-third of an individual’s contacts in normal circumstances are with household members, mask wearing outside the home is assumed to impact the approximately 67 percent of total contacts that are outside the home. Recognizing that some transmission may also be occurring via fomites (including via touching masks), we model the effectiveness of masks as a net 13 percent reduction in infectiousness by asymptomatic individuals. Additionally, we assume mask wearing reduces transmission by pre-symptomatic individuals," assuming someone who ultimately shows symptoms has been infectious for the prior eight days.

The bottom line: Masks help prevent the spread of COVID-19 in several ways, but they're far from magic bullets. While this report won't dissuade many of us from wearing face coverings, you can expect the growing anti-mask contingent to view the statistics very differently even as Denver's death toll continues to rise.

Click to read "Findings on the COVID-19 Epidemic in Colorado to Date and Projections for Future Scenarios of Social Distancing."