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Comment by merpnderp | Hacker News Reader

Saying cloth masks are effective in the context of (K)N95 masks is even worse misinformation. Even the CDC's website on masks points out you should really be using (K)N95's, and that cloth masks are completely ineffective when wet, which they get after 15 minutes or so of breathing through them. The science on cloth masks says they work, but only shortly and just barely. Rand Paul is closer to the truth by saying they don't work than someone else saying they offer robust protection.

Yet Youtube isn't banning anyone who says cloth masks will keep you safe, which is extremely dangerous misinformation.

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> you should really be using (K)N95's

Better masks are obviously better.

> completely ineffective when wet,

As far as I know this is not correct. I remember to have read a study showing quite well that even a wet cloth mask(1) still contains the spread of aerosols surprisingly well. Sure it's far worse then a medical mask of any kinda but still a surprisingly high improvement compared to the no-mask scenario.

> which they get after 15 minutes or so of breathing through them.

In my personal experience this is far from correct, through this depends on the definition of "wet" and the weather.

(1): As long as they are not made of a specific kind of material, which e.g. is often used for bicycle masks and sometimes for scarfs which might from the get to go make thinks worse by splitting the aerosols into smaller lighter ones without stopping them at all.

If you're referring to the material used in most goiter style masks, then I can vouch for it doing nothing more than the aerator filter on your kitchen sink. Yet this is accepted by "science following" industries as an effective mask against an aeresol-transmitted disease. I get the "better than nothing" argument but forgive me for not feeling comfortable with the "any mask is fine" messaging. Either recommend/advertise/mandate masks that are tested to prevent spread of infection and fit tested when appropriate, or drop it.

> not feeling comfortable with the "any mask is fine" messaging.

Sure, there is a reason that in Germany they moved from "any mask" to "medical" mask to requiring FFP2/(K)N95 masks.

> As far as I know this is not correct.

I'm just going by the CDC's webpage on masks showing a big red X next to using masks that are wet or dirty.

https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-si...

I've heavily worked out for 2 hours and worked in the office for 8 hours with a cloth mask without wetness issues. My experience may not be the same for others, but 15 minutes is an exaggeration. As early as April 2020 there was research indicating 2 layer cloth masks were at least 70% as effective as surgical masks, and the ones I have seal much better! Not to mention most people are wearing poorly fitted accordion style masks, not wearing N95 masks.

Either your "heavy workouts" are not heavy, or you are the sand guy from the mummy.

Lol, I was going to reply that maybe he lived in the desert. I just put my undershirt up to my mouth and breathed deeply through it 5 times, and it was pretty damp. I don't think it is controversial that humans expel a lot of moisture through breathing.

Perhaps you could point us to what cdc website you are referring to? Because on cdc.gov wearing a multilayer cloth mask is recommended, and they cite a number of studies on the effectiveness of masks which all show significant reductions in transmissions in people and populations which where masks vs those who don't. See "Human Studies of Masking and SARS-CoV-2 Transmission" on this page:

https://www.cdc.gov/coronavirus/2019-ncov/science/science-br...

It's notable that the only randomized controlled trial ever conducted for masks and Covid [1] was not listed under the personal protection section of this page, and was instead was inaccurately summarized:

> A community-based randomized control trial in Denmark during 2020 assessed whether the use of surgical masks reduced the SARS-CoV-2 infection rate among wearers (personal protection) by more than 50%. Findings were inconclusive,54 most likely because the actual reduction in infections was lower.

This is inaccurate, and should make anyone doubt the judgment of whomever wrote this summary. The paper in question was quite clear that there was no statistical significance between groups:

> The between-group difference was −0.3 percentage point (95% CI, −1.2 to 0.4 percentage point; P = 0.38) (odds ratio, 0.82 [CI, 0.54 to 1.23]; P = 0.33). Multiple imputation accounting for loss to follow-up yielded similar results. Although the difference observed was not statistically significant, the 95% CIs are compatible with a 46% reduction to a 23% increase in infection.

To characterize this as "inconclusive" is misleading at best, dishonest at worst. In general, I find this page to be a highly selective reading of the available literature, which was (and remains) predominantly inconclusive regarding the effectiveness of masks. Even the WHO meta-analysis of mask literature found only a weak positive effect after mixing together the results of studies ranging from cloth masks to respirators, in medical (most of the data) and non-medical settings [2]. This CDC page has instead chosen to lean on a few poorly controlled observational and/or correlative studies, and ignore the higher quality evidence that came before.

[1] https://www.acpjournals.org/doi/10.7326/M20-6817

[2] https://www.thelancet.com/journals/lancet/article/PIIS0140-6...

Ok so you say that characterizing the results as incoonclusive results is dishonest, but in the article the limitations sections literally lists "Inconclusive results" as their first item.

On top of that they state: "Although the difference observed was not statistically significant, the 95% CIs are compatible with a 46% reduction to a 23% increase in infection."

Which sounds like their saying they can say with 95% confidence that there is between a 46% reduction and a 21% increases, which sounds pretty damn inconclusive to me.

The between-group results are not "inconclusive" -- they found no statistically significant difference between the masked and unmasked cohorts. There's no reason to reject the null hypothesis ("masks are not protective") based on this data.

The authors say this:

> The most important limitation is that the findings are inconclusive, with CIs compatible with a 46% decrease to a 23% increase in infection.

This is not saying that that study is inconclusive. It's saying that the protective effect is inconclusive -- masks could be anything from slightly protective, to slightly harmful. The fact that the writer characterizes the entire paper as "inconclusive" is incriminating: it's an editorial bias, a complete misunderstanding of statistics, or a combination of both.

> Which sounds like their saying they can say with 95% confidence that there is between a 46% reduction and a 21% increases, which sounds pretty damn inconclusive to me.

No. They're stating the confidence interval on the point estimate. All point estimates have confidence intervals, and the existence of a confidence interval does not mean that the result is uncertain. To restate basic statistics: the top-line conclusion of the study is that the 95% confidence intervals of the two groups overlap to such a degree that you can't reject the conclusion that they're the same.

I didn't mean to say the fact that the interval exists makes it uncertain, I meant to say the fact that it is a 67% spread makes it uncertain. They are saying that they have narrowed the effect down to within that spread with a 95% chance. That combined with sources of uncertainty not covered by that intervale (Listed in their limitations: missing data, variable adherence, patient-reported findings on home tests, no blinding, and of course inconclusive results) definitely make it sound pretty inconclusive.

There is also the limitation that there was "no assessment of whether masks could decrease disease transmission from mask wearers to others."

The article explicitly states "The findings, however, should not be used to conclude that a recommendation for everyone to wear masks in the community would not be effective in reducing SARS-CoV-2 infections, because the trial did not test the role of masks in source control of SARS-CoV-2 infection."

> That combined with sources of uncertainty not covered by that intervale (Listed in their limitations: missing data, variable adherence, patient-reported findings on home tests, no blinding, and of course inconclusive results) definitely make it sound pretty inconclusive.

The study is not inconclusive. The study failed to reject the null hypothesis. That much is definitive.

Whether or not there might be some smaller difference that the study wasn't powered to detect...we don't know. It's still a definitive rebuttal of any claim that "masks reduce personal risk of infection by 50%", and the fact that it's not in the "personal protection" section of the CDC webpage is simply editorial bias. At the very least, this paper is the best study ever performed on masks and SARS-CoV2, and it severely limits any real-world claim of protectiveness.

> There is also the limitation that there was "no assessment of whether masks could decrease disease transmission from mask wearers to others."

The study wasn't designed to do that. It should still be in the "personal protection" section of the CDC webpage, and is not.

I bought a washable cloth mask. It claimed to be fancy, with "three layers!". Unfortunately, those three layers are polyester, and are impenetrable to air, so all of my breath in and out is through the gaps in the nose area/bottom. I went back to cheap medical masks. At least I know air is passing through it, so there must be some filtering.

KN95's are readily available in the US on Amazon. Your local university likely even keeps a list of brands which have been tested and pass the KN95 certification test. Mine does, and it has been extremely nice having a supply of cheap, safe, high quality masks my local uni has tested.

And since they are KN95, you aren't taking masks away from medical professionals.

Edit: map is just Sydney.

Australia is currently attempting to contain the spread of the Delta strain.

You can see the map here https://www.health.nsw.gov.au/Infectious/covid-19/Pages/case...

Anecdotally, based on what friends are saying about their neighbourhoods, the major hotspots have lower mask wearing compliance, and possibly compliance on visiting households.

I live in an area with almost no cases. Mask wearing is very common especially indoors. But people are still going to shopping centres. So congregation of people is not a differentiating factor in my opinion. Shops are quite busy during the day and social distancing is less than ideal. Especially with WFH, and cafes and restaurants still open for take away. People hang out outside shops.

I believe testing in my area is also high. When there was a few cases near me, I went to 2-3 testing locations to find the shortest queues. All were packed. People not wearing masks are so far outside, social distancing, in a park exercising with social distancing. There is a lot of different masks. Surgical, cloth, some of those fancier reusable ones.

So maybe masks work well enough to make a difference.

There is little reason to doubt a well fitted (K)N95 or other counterpart works well. But cloth masks are unproven to help and there are many other variables that could be in play here. For instance, people who wear masks might spend much less time within 6' of each other, be more likely to be vaccinated, or some other confounding factor to mask effectiveness.

Also I've not seen a single cloth mask particulate test that has tried to reproduce the dampness level of a cloth mask that's been worn for an hour. In any but the driest climates that mask will be damp and much less effective.

And given how few studies have been done on cloth mask efficacy over the last year, it is likely the experts already know that cloth masks don't do much.

My argument isn't that people shouldn't wear masks, it's that now that cheap, plentiful, effective quality masks are available, people are still being told to wear cloth masks. I assume that's the same confusion that got the Senator banned from Youtube.

For instance, people who wear masks might spend much less time within 6' of each other, be more likely to be vaccinated, or some other confounding factor to mask effectiveness.

Neither of those factors are true where I am and there are very few new cases. I don’t deny that there could be confounding factors. But, and I’m using the word literally correctly here, my supermarket is literally operating as normal with social distancing almost impossible. You can’t even walk past someone in an aisle correctly distanced.

And forget about getting vaccinated. It’s very hard to get an appointment here.

I’m not sure what other confounding factor is powerful enough to counteract hundreds of people in close proximity breathing the same air if cloth masks have an insignificant effect.

> I’m not sure what other confounding factor is powerful enough to counteract hundreds of people in close proximity breathing the same air if cloth masks have an insignificant effect.

The difference in populations. If your population is younger, fitter, lighter skinned (and that's just three of the most important of the many factors found in severity of the disease) then there could be the same number of cases in both populations but yours has a higher number of asymptomatic or symptomatic but self-misdiagnosed cases.

Unless both populations are being mass tested weekly? Or do they only get a test if they show symptoms…

Cloth masks might not keep you safe. They do, however, improve safety for those around you. Anything that reduces droplet velocity and interferes with aerosol disperson is by definition better than nothing.

(I didn't downvote), I see what you're saying, but it is complex. If you spend an hour in a poorly ventilated classroom/office space/cubicle farm full of people, and your cloth mask gets damp from your breath, and the CO2 level hits 2000+ meaning the air circulation is extremely poor, is it really believable that a cloth mask is doing anything at all?

A well fit KN95 is drastically preferable, readily available, and highly affordable. No idea why these aren't being promoted as the only safe choice.

Because (at least in the US) the “optics” of a “KN95 as the only safe choice” message would be that the past encouragement of the cloth varieties as reasonably effective was wrong.

It would further decrease the credibility of the government/CDC/Fauci because it would be perhaps the (fourth or fifth?) shifting mask advisory that we have seen in the last 18 months.

Don't understand the downvotes ...

basic science: "Anything that reduces droplet velocity and interferes with aerosol dispersion is by definition better than nothing." here are some supercomputer simulations: https://www.youtube.com/watch?v=GAvO_QdO9eM

This site is full of people who, in defiance of Feynman, are absolutely sure that they're the ones who will finally come up with a way to fool Mother Nature. They don't care about science, simulations, or common sense.

To be fair, as insufferable as this attitude can be, it's probably necessary in order for progress to happen. It usually drags us in the other direction, though.

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