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Latest research shows the decreasing efficacy of used surgical masks

surgical masks efficacy
Photo via Marco Verch Professional Photographer and Speaker/Flickr (CC BY 2.0)

As the coronavirus vaccines from Pfizer and Moderna continue to roll out across the U.S., experts still say people will have to continue wearing masks even after they’ve been inoculated. 

Although the U.S. has now surpassed 4,000 coronavirus deaths per day, 12 states still don’t have a mask mandate (though Wyoming just implemented one for the first time in mid-December). And Dr. Anthony Fauci has said the pandemic could get even worse in the U.S. after the Christmas holiday than it was in the weeks following Thanksgiving. January could be the worst month since the pandemic began. So, while there’s hope surrounding the new vaccines, it’ll still be quite a slog before life gets back to normal. 

That’s why the continued wearing of masks in our everyday lives is imperative. More research continues to emerge about the masks and whether they should be worn to help stave off coronavirus transmissions, and the vast majority of it shows masks are vital to keep people safe from COVID-19. Recently, one of South Dakota Gov. Kristi Noem’s advisers said, “I’m still waiting for someone to point me to where in the world mask mandates are working.”

Well, here’s a sampling of some of the newest studies to be published along with other research we continue to discover. 

–Xi, J.,  Xiuhua A., and Nagarajan, R. (2020). Effects of mask-wearing on the inhalability and deposition of airborne SARS-CoV-2 aerosols in human upper airway. Physics of Fluids. https://aip.scitation.org/doi/10.1063/5.0034580

Researchers from two American universities showed that surgical masks are 65% effective in filtering out particles from the air, but the longer a mask is worn, the more that percentage drops. And according to the study in the Physics of Fluids, wearing a used and/or soiled mask might be even worse than not wearing a mask at all. That’s because a used three-layer mask can’t filter out as many particles as a brand new one. 

“It is natural to think that wearing a mask, no matter new or old, should always be better than nothing,” author Jinxiang Xi said, via the New York Post. “Our results show that this belief is only true for particles larger than 5 micrometers, but not for fine particles smaller than 2.5 micrometers.”

The authors used a computational model that included a “pleated surgical mask, a face model, and an image-based upper airway geometry.” Results showed that air enters the mouth and nose at slower speeds when a mask is worn, and over time, the mask’s efficacy decreases. 

“We hope public health authorities strengthen the current preventative measures to curb COVID-19 transmission, like choosing a more effective mask, wearing it properly for the highest protection, and avoid using an excessively used or expired surgical mask,” Xi said.

–Anfinrud, P., Stadnytskyi, V., Bax, C. and Bax, A., (2020). Visualizing Speech-Generated Oral Fluid Droplets with Laser Light Scattering. New England Journal of Medicine, 382(21), pp.2061-2063. (May 2020) 

In a letter sent to the New England Journal of Medicine, a trio of researchers described how they reported “the results of a laser light-scattering experiment in which speech-generated droplets and their trajectories were visualized.” 

More from the letter from April 2020: “The output from a 532-nm green laser operating at 2.5-W optical power was transformed into a light sheet that was approximately 1 mm thick and 150 mm tall. We directed this light sheet through slits on the sides of a cardboard box measuring 53×46×62 cm. The interior of the box was painted black. The enclosure was positioned under a high-efficiency particulate air (HEPA) filter to eliminate dust. When a person spoke through the open end of the box, droplets generated during speech traversed approximately 50 to 75 mm before they encountered the light sheet.”

The researchers found that when a person said “stay healthy,” a number of drops produced flashes on the light sheet, and the highest number of flashes occurred when the “th” sound in the word “healthy” was said. The louder a person said “stay healthy,” the more flashes there were. When a slightly damp washcloth was placed over the mouth of the speaker, representing a mask, there was a decrease in flashes, meaning the forward-movement droplets had been reduced. 

Wrote the researchers, “Our aim was to provide visual evidence of speech-generated droplets and to qualitatively describe the effect of a damp cloth cover over the mouth to curb the emission of droplets.”

In case you missed the last blog post, the spotlighted research showed that the vast majority of people at West Virginia University were correctly wearing their masks, while, in other news, there was controversy surrounding a Danish randomized control study of nearly 5,000 people. 

Josh Katzowitz

Written by Josh Katzowitz