Let’s face it, guidance on mask use during the coronavirus pandemic hasn’t always been clear. That’s unfortunate, because we have known long before the current pandemic that masks that fit well and have good filters have historically protected medical workers and patients from infection by airborne viruses. New CDC studies have been completed that give clear data on why masks are effective and subsequently, new guidelines were given on proper mask fit to be most effective.

Does Masking Guidance Change After Vaccination? 

Now that vaccines are getting into people’s arms, new CDC guidance(1) says that it’s safe for fully vaccinated people to hang out indoors unmasked without social distancing. They also say that fully vaccinated people should be safe to similarly visit with lowrisk unvaccinated people (i.e. vaccinated grandparents can finally visit their grandkids). That said, masks are still going to be around for a while longer. 

What Kind of Mask Should I Use? 

Healthcare workers have been effectively using N95 masks since the start of the pandemic to dramatically reduce their chances of getting an infectious dose of coronavirus during their workday. With global mask shortageshospitals have competed with the public for surgical masks and N95 masks. It wasn’t initially clear how effective a public pandemic policy of home-made cloth masks would be, since we didn’t know how effective cloth masks were, and didn’t know how people would behave when wearing them. We now know that the best home-made cloth masks have filter effectiveness on par with surgical masks (2)The best cloth masks are tight-fitting, with multiple layers of tightly woven cloth (3 is good), including a polypropylene layer for static charge. 

Summary of New Research on Mask Effectiveness 

With a global effort underway to ramp up PPE production, surgical masks are now readily available for the general public. Given reports that the UK variant of coronavirus is more transmissible (and more deadly) (3), the CDC is interested in ways to improve the effectiveness of masks in the public. Surgical masks are made with pretty effective filter material to begin with. The biggest weakness of surgical masks is that they tend to leave large gaps on the sides for unfiltered air to bypass around the mask. Because of this, the CDC has decided to focus on improving the snugness of fit for surgical masks4. 

First, the CDC tested how effective a mask was at blocking a single cough at the source. A dummy head was rigged to wear a mask and blow a puff of aerosol into it. 3-layer cloth mask and a surgical mask each individually blocked just over half of the aerosol particles coughed out. Altering the mask fit by tying a knot near the base of the elastic bands on each side of a surgical mask and tucking the sides down flat increased the filtration to 77%. When a cloth mask was placed over a surgical mask, the effectiveness jumped up to 85.4%. 

CDC demonstration of three mask fits that were tested on dummies

Second, they built an experimental setup inside a 10’X10’ room with dummy heads facing each other 6 feet apart. For 15 minutes, one dummy (the source) would blow out aerosol and the other dummy (the receiver) would suck in airUsing different configurations of mask use, they tested the amount of aerosol collected in the mouth of the dummy breathing in. There’s a lot of data to process, so I’ll try to summarize the key things that jump out. 

When the source of the aerosol was unmasked, adding a surgical mask to the receiver only reduced aerosols inhaled by 7.5%. However, the reverse situation (the source of the aerosol had a surgical mask and the receiver was unmasked) reduced aerosols inhaled by 41.3%. When both occupants wore surgical masks, inhaled aerosol was cut by 84.3%. This is why we should all wear masks around others outside our small cohort. While aerosols still get passed around, universal mask use greatly reduces the chances of inhaling enough virus for an infectious dose. 

Data on effectiveness of different mask fits and usage

The wildest bit for me is that when you look at the data for double-masking (cloth over surgical), there’s over 80% reduction in aerosols inhaled if EITHER ONE of the occupants is wearing a double-mask. If BOTH are double-masked, you get 96% reduction in inhaled aerosols. You can even get a 96% reduction if both occupants are simply wearing surgical masks knotted and tucked, with over a 60% reduction if only one of the occupants is masked.  

So, Should We Wear a Mask? 

Because of this data, the CDC is now recommending methods to improve surgical mask fit when in publicSimply put, wear a cloth mask or nylon (neck gaiter) mask over a surgical maskuse a mask fitter device, or use the tie and tuck method to get a snug mask fit and best filtration effectiveness. You’ve got to love simple measures like this for reducing transmission and saving lives. 

CDC: A tightly fit mask can limit the spread of the coronavirus

(1) CDC – Interim Public Health Recommendations for Fully Vaccinated People 

(2CDC – Scientific Brief: Community Use of Cloth Masks to Control the Spread of SARS-CoV-2 

(3CDC – Emerging SARS-CoV-2 Variants 

(4CDC – Maximizing Fit for Cloth and Medical Procedure Masks to Improve Performance and Reduce SARS-CoV-2 Transmission and Exposure, 2021 

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