TORONTO —
Face masks made with multiple layers of cloth may help prevent further transmission of COVID-19, according to an international team of researchers who examined a century’s worth of mask studies.

Homemade cloth masks aren’t perfect, they found, but may help provide a “modest reduction in transmission” if widely used, according to the opinion paper published in the Annals of Internal Medicine on May 22.

“At their best, cloth masks can be really quite good and are definitely worth considering under the circumstances,” said lead author Catherine Clase, associate professor of medicine at McMaster University and a nephrologist of St. Joseph’s Healthcare in Hamilton, Ont.

The team’s full review of mask research has yet to be published, but is currently being peer-reviewed as scientific journals ramp up their assessment of COVID-19 research, said Clase.

The team of international scientists looked at 100 years of research, going back to the 1918 Spanish flu pandemic when scientists sprayed bacteria on gauze to see how the thread count and layering impacted transmission.

A century later, there is still a lack of evidence to support the effectiveness of homemade masks in preventing community transmission.

“There are no clinical studies that show wearing a mask out in the community is definitely going to reduce the transmission of a viral illness,” said Clase. 

Studies have long demonstrated the effectiveness of medical grade personal protective equipment in a clinical setting, but Clase said that since those medical masks should be reserved for front-line workers, their research focused on homemade cloth masks. 

But there is not yet enough evidence for scientists to definitively recommend a specific type of cloth or a specific method for creating a homemade masks.

Nevertheless, the more than 20 studies of cloth masks Clase and team have identified examined woven material like cotton, linen, muslin and flannel.

Complicating matters further, layering cloth increases effectiveness but decreases breathability. “If you can’t tolerate wearing the mask then obviously you’re not going to wear it,” said Clase.

The other “unintended consequences” of homemade cloth masks are social, she added. “The biggest fear that we would have is that wearing a cloth mask would lead to a false sense of security,” she said, which could lead to reduced hand hygiene and physical distancing.

While the research is incomplete, there is still enough “convincing” evidence that should inform policy decisions during the COVID-19 pandemic, the researchers wrote.

The novel coronavirus SARS-CoV-2 is transmitted through aerosol and droplet particles that people generate while speaking, eating, coughing and sneezing, and cloth masks can stop those particles in their tracks before they can transmit the virus. “Every virus-laden particle retained in a mask is not available to hang in the air as an aerosol or fall to a surface to be later picked up by touch,” the researchers said.

Evidence or not, the use of masks is “intuitive,” says infectious disease expert Dr. Abdu Sharkawy.

“If we have a disease and we’re able to protect our mouths from having that spread to someone who is unavoidably within six feet of us, it only makes sense that it’s going to help at least on some level,” he said on CTV News Channel on Monday. “The principle should be that masks will help. There’s no reason why we shouldn’t be able to wear them in most circumstances to help prevent the spread of this infection.”

But masks are not an “isolated strategy,” he added, naming physical distancing and hand-washing as other elements of an “overarching strategy” to prevent infection.

“Truthfully, it’s probably much more important to keep a physical distance than to wear a mask,” he said.



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