Lai et al. just published a paper looking at how well various masks worked for keeping others from getting sick (“source control”). Their university press office
summarized this as:
Study finds all masks effective, but ‘duckbill’ N95 masks
far outperform others, suggests they should be the standard in
high-risk settings
Now, I personally think duckbill masks are the best disposable masks:
they’re cheap, comfortable, fit me well, and are more breathable due
to their larger area. Plus, as masks that manage to be unfashionable
even by the standards of N95 masks, if they weren’t better in
non-fashion ways they wouldn’t be on the market anymore. But the study
didn’t show that they’re the best kind of N95, only that they do
better than the other masks they tested, none of which were N95s.
The study compared five conditions: no mask, cloth mask, surgical
mask, KN95, and (duckbill) N95. This isn’t a study that can tell you
anything about the differences between N95s!
To me the most interesting parts of the study were (a) they captured
the viral RNA and measured viral load with qPCR instead of using bad
proxies like particle count and (b) they found KN95s did way
worse than you’d expect from their filtration efficiency:
The majority of the KN95 respirators used in our study
(reported by an N95docon.org to have
consistently high filtration efficiency but variable and high flow
resistance) did not outperform loose-fitting masks and when including
other brands, KN95s met inferiority criteria compared to cloth masks
for total viral aerosol. One possible explanation is that we noted
that the KN95 respirators we provided were relatively stiff and did
not seal consistently along the entire perimeter of the mask. By
contrast, the cloth masks brought by our volunteers tended to wrap
farther around the face possibly providing better fit and lower flow
resistance. We used one surgical mask brand for these tests so that
result may not be representative of all masks; the same brand used
in prior CDC-funded studies of masks for influenza source control.
The relatively high flow resistance of KN95 filters, compared with
surgical and cloth masks, combined with poor fit tended to promote
leaks around the face seal.
I recall a lot of people (including us) using clips to convert the
KN95′s elastic ear loops into a behind-the-head attachment, for a much
tighter-fitting seal. It would be interesting to see if that’s enough
to make up the difference!
(I wonder if this means that events that require “high-filtration”
masks should switch to explicitly requiring N95s or better, now that
those are widely available?)
Duckbill Masks Better?
Link post
Lai et al. just published a paper looking at how well various masks worked for keeping others from getting sick (“source control”). Their university press office summarized this as:
Now, I personally think duckbill masks are the best disposable masks: they’re cheap, comfortable, fit me well, and are more breathable due to their larger area. Plus, as masks that manage to be unfashionable even by the standards of N95 masks, if they weren’t better in non-fashion ways they wouldn’t be on the market anymore. But the study didn’t show that they’re the best kind of N95, only that they do better than the other masks they tested, none of which were N95s.
The study compared five conditions: no mask, cloth mask, surgical mask, KN95, and (duckbill) N95. This isn’t a study that can tell you anything about the differences between N95s!
To me the most interesting parts of the study were (a) they captured the viral RNA and measured viral load with qPCR instead of using bad proxies like particle count and (b) they found KN95s did way worse than you’d expect from their filtration efficiency:
I recall a lot of people (including us) using clips to convert the KN95′s elastic ear loops into a behind-the-head attachment, for a much tighter-fitting seal. It would be interesting to see if that’s enough to make up the difference!
(I wonder if this means that events that require “high-filtration” masks should switch to explicitly requiring N95s or better, now that those are widely available?)
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