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I'm not sure how generally applicable this is, but I found it interesting:
A study on the effectiveness of different kinds of medical masks against covid transmission. The researchers found that the ACI 3120 N95s (the duckbill masks I like) are 98-99% effective at blocking exhaled virus particles. However, surgical masks and a specific kind of KN95 masks were both less effective than N95 masks; surprisingly, Powecom KN95s were less effective than surgical masks.
The researchers didn't train anyone on how to use the masks, which is a more realistic test of real-world effectiveness, because most people aren't doing fit tests, and many aren't reading the instructions that come with the masks.
The study was testing how effective the masks would be in preventing a person who had covid from spreading the virus to people around them, not how well the mask wearer is protected from viruses in the air. not how well they protect the wearer from viruses in the environment.
The article notes several limitations, including a small sample size; that all the study subjects were young adults; and that it may not generalize to different models of N95s or KN95s. Also, the study was testing how effectively the masks would block transmission if the wearer had covid, not how effectively wearing a mask protects the wearer.
(Armbrust is currently offering 40% off, with the code WASTEWATER40)
[Edited the first paragraph to clarify that they only studied one kind of KN95s.]
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The results become meaningless if they insist on the limits they are using (in this case not even testing a wide range of products).
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Limited population and masks: probably because of limited grant/budget.
People do study protection of the wearer. But demonstrating protection against disease is much more involved: you either need to deliberately try to infect people in a lab (hopefully with some more benign virus), or to track a lot of people for a long time, and that has problems like "how well and how often did they wear a mask?", aka "did the mask fail or did they not wear a mask at the wrong time?"
Note that this study was simply measuring virus particles escaping the mask, not lowered infection rates or something, and the reverse of that -- how many particle get into a mask -- is done all the time; it's how N95s are certified and how employees are fit tested for them in the workplace.
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https://journals.asm.org/doi/10.1128/cmr.00124-23
It combines the results of over 100 studies so should provide the breadth and depth to get a clear picture.
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I suspect few people are still using homemade cloth masks, but on the other hand I saw someone on the bus using a bandanna as a mask only a few months ago. I don't remember whether it was a day on which people were likely to be protecting against air pollution or pollen,
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More precisely, as they admit, one stiff KN95 was worse than the cloth mask they tried.
The strongest conclusion from the paper is "wear a duckbill".
Also I've messed up; somehow I thought they'd tested Vflex, not some other duckbill. Oops.
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seems like any mask worn and "sealed" properly is far better than none at all. I've gradually gotten back in the habit since it seems everyone is going down with another round of Plague this summer.