Monday, January 10, 2022

Why are we still confused about the effectiveness of different masks?

It's difficult to believe that we are still having discussions about the relative merits of different kinds of masks at this point, nearly two years into the pandemic. But it seems we are. There are differing opinions still, even within Canada's provinces.

All the studies I have seen suggest that N95 and KN95 masks (or respirators, as they are sometimes, confusingly, referred to), along with similar or equivalent masks like the Korean KF94 and the European FFP2, are substantially better at filtering out viral particles than regular (blue) surgical or medical masks, partly because they tend to fit better, and partly because they have more layers. And both are a lot better than the cloths masks that most of us have been using throughout most this pandemic. Cloth masks may have cut it for the early variants (maybe); surgical masks may have cut it even for the Delta variant; but only N95s/KN95s are up to the job against the much more contagious Omicron variant. This we know, and have known for some time. 

One major recent Ontario study concluded that N95 masks filter out about 60% of aerosol particles (which is what we need to be focusing on), and KN95s filter out about 46%. This a lot less than the 95% they are named for, but these are real world figures. And compare it to 12% for surgical masks and 10% for cloth masks the same study yielded! Another study of the effectiveness of different masks against aerosols gave figures of 83-99% for N95/KN95 masks, 42-88% for surgical masks, 16-23% for cloth masks, and just 9% for bandanas. You get the idea. A surgical mask with a cloth mask on top (NOT the oher way round) can also be a reasonably effective combination, although still not to the level of a N95/KN95.

Canada's Chief Public Health Officer, Dr. Teresa Tam, has been touting the benefits of N95/KN95 masks for some time now, as has most of the medical profession. So, why then is BC's Provincial Health Officer, Dr. Bonnie Henry (who was the poster-girl for sensible coronavirus advice in the early part of the pandemic), talking about the "incremental benefit" of N95s, and saying it is more important that whatever mask you wear fits well. Worse, why is Alberta's Chief Medical Officer of Health, Dr. Deene Hinshaw, saying things like,"There is very little evidence that, in a community setting, using N95 masks is going to provide a significant additional benefit". Talk about mixed messages (although that has been Alberta's approach throughout)! 

Yes, N95s are more expensive than surgical masks (KN95s are a bit more affordable), and they are admittedly more difficult to find (although my understanding is that medical personnel are no longer unable to obtain needed supplies, as they were earlier in the pandemic, so we would not be depriving them of scarce, necessary PPE). So, if you are going to be spending substantial amounts of time indoors in a public space, whether you are a teacher or a student or a shop cashier, whether you are travelling on public transit or waiting for treatment in a clinic waiting room - wear a mask, and do all you can to make sure it is a N95 or KN95 mask.

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