[samatman]

Ironically, WHO and CDC have done bad messaging on both sides of this. I get slammed every time I bring this up now, because the issue is politicized and, let's be honest, pretty traumatic as well. But I think it's important so I'll keep trying.

Everyone should have been masking up as soon as possible in the pandemic. Case counts were low, we didn't know much about the route of transmission, and we also thought it was even more dangerous than it turned out to be. Precautions were indicated, but health authorities were decrying mask use as late as the end of March.

But it turns out that the primary vector is aerosols, not droplets or fomites. Any mask will mitigate droplet contamination, and the resulting fomites: this is why influenza has practically disappeared, masking is very effective against influenza, where those are the primary vector.

But no mask will do much to filter aerosols on exhalation. That's simply not how they work, positive pressure puts most of the gasses out through the sides of the mask. Even a P100 filter with cartridges won't do it, that's why they have a vent, otherwise the face seal would be broken every time one exhales. To be generous, I'll say that a cloth mask catches 30% of aerosols. It doesn't, but say it does: that's not nearly good enough. Which case counts after universal masking mandates illustrate quite clearly: they rise, and fall, and the masks don't have anything to do with it.

A good mask will filter some aerosols when inhaling: but a cloth mask won't. So once aerosols were identified as the culprit, WHO and CDC should have emphasized air filtration, which is quite effective, limiting the number of people indoors on the basis of how many air exchanges a HEPA or ULPA filter was capable of doing. Messaging should have emphasized that cloth and surgical masks are completely useless, and that at-risk people should stay home, and if they can't, should get a proper mask (KN94, (K)N95, P100) and learn how to use it. COVID doesn't survive on surfaces very long, so reuse is more-or-less ok, and there were plenty of proper masks by June, which is when these facts were available. If WHO and CDC had listened to them.

I vape, so I can illustrate this to myself quite easily: I can hit the vape through a cloth mask, but not a KN94. And with any mask, I can take a hit, put it on, and exhale a visible cloud of, yep, aerosols, around the side of the mask.

I still wear a KN94 indoors, it's the best I can do. But I'm walking around in indoor spaces with no HEPA filters, surrounded by people who are unprotected, just wearing a talisman. This was preventable.

[octodog]

Do you have any sources for cloth or surgical masks not working?

The study in this article [0] is still in pre-print but it claims that a change to mandatory mask wearing was a critical factor in crushing the virus in Melbourne's second wave.

I've seen some comments on HN that masks aren't effective but from what I've read and observed in Melbourne/Australia they have been very effective.

[0] https://www.abc.net.au/news/2021-04-14/face-masks-number-one...

[samatman]

See some sibling comments for my specific thoughts on the matter.

Melbourne did everything they could think of, and the sum of it worked. This included a very severe lockdown, contact tracing, masking in the very limited public interactions which were allowed, and starting with a relatively low case count. I'm fairly confident that masks were the least important part of this, and that shutting down basically every part of public life was the most.

I did say that masking early on was indicated, and that WHO and CDC failed us there. I sort of glossed over the part where case counts were low, but it's there, and it's pretty important.

What the US and Europe needed early is what New Zealand and Australia (and Taiwan, Korea, maybe a couple other Southeast Asian countries) actually managed: universal masking, a nearly-complete cessation of public life, widespread testing, contact tracing, and central quarantine for the infected. Instead, we got dithering and "wash your hands".

It was too late for that suite of interventions to be effective by 1st April at the latest. Earlier for Europe, which had the early wave epidemic in Italy.

So of course, that's when masking was adopted, as a totemic symbol that the powers that be were "doing something". But we had crossed the point where it could help, and it was always the least important thing.

[kelnos]

> See some sibling comments for my specific thoughts on the matter.

I took a look at your sibling comments, but I don't see any sources linked that suggest cloth masks are so ineffective as to be useless.

Here are a couple studies suggesting they aren't useless (searched "cloth mask aerosol protection" via DDG):

https://pubs.acs.org/doi/10.1021/acsnano.0c03252 (effectiveness had a very wide range, depending on weave, thread count, etc.)

https://www.nist.gov/publications/filtration-efficiencies-na...

I get what you're saying in general, that "cloth mask" means many different things, and that those things aren't going to have the same levels of protection, but you seem to be pushing the idea -- without evidence -- that all cloth masks are worse than useless. Science doesn't seem to agree with you?

[viraptor]

> A good mask will filter some aerosols when inhaling: but a cloth mask won't.

There's an issue with statements like that. "Cloth mask" is not well defined - are we talking literal layer of cloth, or the cloth-synthetic-cloth design recommended in some countries. Either way there's some gradient between 100% protection and nothing - cloth masks will still be better than nothing, but purpose-designed masks will outperform them.

This is not a trivial scenario to talk about, so the more specific we are the better.

[samatman]

Alright, that's a decent point. KN94 is cloth, after all, and it's what I use. I was using "cloth mask" colloquially to refer to the masks made of ordinary cloth which have become pretty much standard uniform in the parts of the US with mask mandates. You can do a little better with multiple layers and tighter weaves, but, not much. If it's not specifically designed to filter particles as small as aerosols, it won't, and if it doesn't have a number after its name, it isn't so designed.

I don't think it's accurate to say that those are better than nothing. The false sense of security could easily lead to people staying longer indoors, or entering indoor spaces which they would consider dangerous if they didn't have the misconception that cloth masks protect them. It's a very small amount of protection, so it doesn't take much moral hazard to overwhelm it.

Could you maybe get a little less sick, if say 10% less viral aerosols passed through the mask? Ok, if I'm going to be very generous, sure. At the margins, someone is going to inhale a sub-infectious dose of aerosol who would have gotten a just-barely-infectious aerosol dose.

But this is like talking about condoms with holes in them. Most of the semen would stay in! It's not as pregnancy inducing as going bare! But I wouldn't call it birth control either.

[samatman]

I don't know if anyone is still reading this, but Wired just published a detailed smoking gun on the aerosols question.

https://www.wired.com/story/the-teeny-tiny-scientific-screwu...

It's really good, I learned a lot of new things. Please read this if you're at all interested in the subject: and who among us isn't at this point?

[tim333]

>primary vector is aerosols, not droplets

Any source for that? I mean it has always seemed likely that both aerosols and droplets would be a factor but where did 'primary' come from?

[samatman]

Here's a discussion of the subject from October:

https://www.scientificamerican.com/article/protecting-agains...

I suggest, without intending to be dismissive, punching "covid aerosols primary" or the like into your search engine of choice and going to town. It's been a long debate, and by late last year every prestigious organization except CDC and WHO were in the aerosols camp. Even they have kind of low-key admitted it, while insisting that the measures to control it they promoted on an erroneous theory are still the correct ones. Which is, of course, nonsense.

A droplet is just a large blob of the same saliva that makes up the aerosols. If it gets in your lungs, it will make you sick. This is pretty easy to avoid behaviorally, and with face shields for workers who have to have contact with the public. Wearing a mask will also mitigate this, but it isn't necessary (just don't point your face at other people) and it isn't sufficient, because of aerosols, which are therefore the primary source of transmission.

When a droplet lands on a surface, it becomes a fomite. Picking these up with ones hands, and transmitting them to eyes, nose, and lips, is a major route of infection for influenza. It does not appear to be a significant route of infection for COVID.

Diseases which spread primarily through droplets do so by forming fomites. Unlike someone spitting on your face, it's very easy to touch a surface someone else spit upon, and people touch their faces a lot.