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1/ I am getting a lot of questions about masks and new variants. Some are calling for a universal N95 policy. Also hearing a lot of experts talk about cloth masks being inferior to surgical masks. Let's take a look at the literature.
2/ First, important to recognize that new variants are thought to be more transmissible because infected individuals have have higher viral loads, and thus presumably higher viral counts in droplets.
3/ However, no reason to suspect that the way we produce droplets, the size of those droplets, or the physics of droplet spread would be any different with new variants.
4/ So with more variants around us, our chances of infection are higher because of higher viral load exposures from infected people in our midst. But droplets are still droplets. Which means it's not that we need better masks. We just need to use the right masks better.
5/ . @GovCanHealth @CDCgov and @WHO all recommend 3 layer cloth masks - 2 tightly woven layers and 1 filter layer (non-woven polypropylene is best). If you can adhere to this, protection is comparable to surgical masks.
6/Some studies have shown that cloth masks are inferior to surgical. But as you will note in this review, those early studies mostly looked at homemade masks from T-shirts, balaclavas/bandanas, or 1-or 2-ply cotton masks (i.e. not what's now recommended): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7553716/
7/ On the other hand, carefully designed studies of 3-layer cloth masks show comparable (and in some cases superior) filtration efficiency vs surgical masks: https://www.cell.com/med/fulltext/S2666-6340(20)30072-6 and https://www.medrxiv.org/content/10.1101/2020.11.18.20233353v1
8/ For those who can't afford disposable masks (many of my patients), who share concerns about the environmental impact of single use masks, and because of the risk of surgical mask shortages for healthcare workers ( https://www.pnas.org/content/118/4/e2014564118), cloth masks continue to have a role.
9/ All that being said, finding a cloth mask with the right material and the right filter can be tricky. And there's no universal standard nor quality control. So in the new variant era, if you are going to use a cloth mask, you need to follow the guidance to the letter.
10/ Also lost in all the loose talk (pun intended) about cloth vs surgical masks, is the importance of fit. Construction and material doesn’t mean much if you’ve got a ton of space around the mask and most of your droplets are escaping around it instead of getting caught in it.
11/ This elegant study showed that a well-fitted cloth mask is far superior to an ill-fitting surgical mask (both do comparably well if they fit snuggly against the face): https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2774266?utm_source=twitter&utm_campaign=content-shareicons&utm_content=article_engagement&utm_medium=social&utm_term=012521#.YA99QtwX4IA.twitter
12/ I've also heard some aerosol scientists recommend universal use of N95 or KN95 masks, and some countries have gone this route. Here is where I think we need to remind ourselves about the difference between efficacy and effectiveness.
13/ Let’s not let the best be the enemy of the good (enough). N95 masks have better filtration efficiencies in in-vitro studies, but studies do not suggest that they are any different than surgical masks for viral transmission in real-world scenarios: https://onlinelibrary.wiley.com/doi/full/10.1111/irv.12745
14/ And let's not forget that in most healthcare settings, including throughout this country, providers use surgical masks for routine care of actively infected #COVID patients (and we have done just fine, thank you).
15/And this saying nothing about need for fit testing, shortages for healthcare workers, and impact on adherence due to discomfort (try spending a day convincing respiratory patients to breathe through a surgical mask, let alone N95)- and for good reason: https://www.atsjournals.org/doi/10.1513/AnnalsATS.202008-990CME
16/ In conclusion, find the right mask, and spend some time making sure the fit is right (i.e. tight!!!). Here's my attempt at squishing all this into a 2.5 minute "mask hack" explainer: https://twitter.com/i/status/1358128829085212672
