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Home-made face masks likely need at least 2 layers to curb COVID-19 spread:
Home-made cloth face masks likely need a minimum of two layers, and preferably three, to prevent the dispersal of viral droplets from the nose and mouth that are associated with the spread of COVID-19, indicates a video case study published online in the journal Thorax.
[...] A team of Australian researchers therefore compared the effectiveness of single and double-layer cloth face coverings (175 g/m² cotton fabric, with a thread count of 170/ inch) with a 3-ply surgical face mask (Bao Thach) at reducing droplet spread.
[...] The video recording showed that the 3-ply surgical face mask was the most effective at reducing airborne droplet dispersal, although even a single layer cloth face covering reduced the droplet spread from speaking.
But a double layer covering was better than a single layer in reducing the droplet spread from coughing and sneezing, the recording showed.
This is just one case, added to which several other factors contribute to the effectiveness of cloth face masks, note the researchers. These include the type of material used, design and fit, as well as the frequency of washing.
Nevertheless, based on their observations, a home made cloth mask with at least two layers is preferable to a single layer mask, they say, adding: "Guidelines on home-made cloth masks should stipulate multiple layers."
And they emphasise: "There is a need for more evidence to inform safer cloth mask design, and countries should ensure adequate manufacturing or procurement of surgical masks."
Journal Reference:
Prateek Bahl, Shovon Bhattacharjee, Charitha de Silva, et al. Face coverings and mask to minimise droplet dispersion and aerosolisation: a video case study [$], Thorax (DOI: 10.1136/thoraxjnl-2020-215748)
(Score: 2) by HiThere on Monday July 27 2020, @11:35PM (1 child)
It appears that catching COVID gives an immunity that lasts for years. (There's a bit of inference there, but it's reasonable.) But it may not be a complete immunity.
The thing is, antibodies appear to last for a couple of months (varies with the individual, but that's an average). But TCell based immunity looks as if it lasts for years. However TCell immunity doesn't work until some cells catch the disease. It's a plausible inference that the reason there are so many "silent spreader" cases is that a lot of people already have TCell based immunity, so the cases of COVID that they catch are so weak that they don't really notice it as anything special. But they can spread it to people who haven't been exposed.
If this is true, it implies that the current COVID is only different by a couple of mutations from something that's been around for a long time, but which people haven't noticed...or have just thought "well, that was a bad flu this year", even though it was something else.
Note that this post is full of a lot of suppositions, so don't believe it. But it's based on actual data, so don't disbelieve it either. Just file it under "maybe" and consider what evidence you would expect to find if it were to be true.
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 2) by PartTimeZombie on Tuesday July 28 2020, @12:29AM
That was kind of the point I was trying to make.
TL;DR: We don't know yet.