Face masks effectively limit the probability of SARS-CoV-2 transmission

https://science.sciencemag.org/content/early/2021/05/19/science.abg6296

324 356 5 years ago

science.sciencemag.org

tryonenow• 5 years ago

Surgical masks with particle collection efficiencies around ~50% cannot prevent the release of millions of particles per person and their inhalation by others (green dots in Fig. 1, B and D). In other words, the human-emitted respiratory particle number is so high that we cannot avoid inhaling particles generated by another person even when wearing a surgical mask

So the entire premise of the modeling in the paper rests on the assumption that surgical masks can filter some percentage of viral particles. It's my understanding that viral particles are around 3 orders of magnitude smaller than the pores in surgical masks. So is there any evidence that surgical masks can filter aerosolized viral particles?

noname120• 5 years ago

Viral particles are concentrated in droplets and aerosols, which are significantly blocked by surgical masks.

splitrocket2• 5 years ago

Virus particles do not travel naked in the air, instead they are colloidally suspended in liquid, both droplets and aerosols.

So, if your filter catches the droplets and aerosols, which are much larger in size than the actual virus, the filter works.

takeda2• 5 years ago

Realization that somebody's droplets are getting into your mouth and nose makes one want to wear mask even after pandemic is over :)

neilwilson• 5 years ago

Except that field data shows they don’t because they are not used precisely as required - which means the filter doesn’t work effectively if at all and then it becomes infectious waste that isn’t treated and disposed of correctly.

Human system effects dominate - as the field data shows. It’s like HCQ - works in a lab, not in the real world.

Might be useful in tightly controlled medical settings with adequate filtered ventilation. But there’s no hard evidence beyond that at this stage.

Feynman’s rule still applies.

abfan1127• 5 years ago

assuming: 1) 100% capture of air flow 2) no fatigue (ie capture is same at t=0, and t=later)

anyone with glasses will tell you 1 isn't a very good assumption. As masks saturate in moisture, back pressure causes (1) to be more false.

blumomo2• 5 years ago

Science is based a lot on assumptions and beliefs. A scientist who does not consciously say: „We have observed that… which makes us believe that…“ still ultimately becomes a victim of his unconsciously formed belief system, a pseudo-religion.

I’m a software engineer, I work scientifically, but I don’t own the truth. I own the thought process which works on top of assumptions. But I don’t want my own work to feel like magic, and to avoid that, I observe and try to understand it. But at the end of the day I have to say: „I assume that my program is bug free because I have observed many test runs in which the program behaved correctly. I belief it will work well at the customer.

Same has to be said for above study. Otherwise we wouldn’t find studies which even claim the opposite. These other studies are just based on different assumptions and belief systems.

cr18954• 5 years ago

Here’s a nice interactive graphic showing how masks block particles:

https://www.nytimes.com/interactive/2020/10/30/science/wear-...

neither_color3• 5 years ago

That's a very cool visualization and I wish I'd seen it before. I am curious though as to what makes some viruses have higher R values than others. These masks more effectively stopped influenza and I still don't understand why.

splitrocket2• 5 years ago

Not that this will settle anything.

Anecdotally, I've not gotten even a slight cold while being socially distanced while consistently masked.

michaelhah• 5 years ago

Well, that may be due to other people social distancing enough to keep the level of colds down. It might have nothing to do with masks.

bryanrasmussen• 5 years ago

anecdotally, I have very little social contact normally anyway, I've worked from home since before winter, and always wear masks in closed public spaces - have had 3-4 colds in that time.

I do have kids though.

space_ghost• 5 years ago

My frequency of colds has increased 10x since I've gotten married and had kids.

jackfoxy• 5 years ago

Anecdotally, since taking vitamin D3 supplements I haven't been getting colds. Added daily nutritional zinc supplements in 2020 as soon as they were available after I heard the anecdotal evidence D & zinc are effective in Covid prevention. Throughout winter and early spring last year you couldn't get zinc supplements for love or money.

A lot of anecdotes there :).

The American medical establishment has a long history of not getting behind nutritional disease prevention. Some of it is for good reason, but I think there is also a systemic bias.

andrew_• 5 years ago

My 2yo would like to sneeze on you and flip that anecdote on its head.

MrDunham• 5 years ago

Parent of a 1.5 year old here. Can confirm - several colds.

To the parent comment's point though, I haven’t had any colds in the last year where my daughter wasn’t sick first

awb3• 5 years ago

Years ago my entire family got sick and I was determined not to contract it through distancing and frequent hand washing and sanitizing. It worked until I bent down to tie my toddler’s shoes only to look up and mid-sentence have him cough directly into my open mouth. All it takes is one mistake. Needless to say I got sick shortly after.

jMyles5• 5 years ago

I'm not sure which explanation you are seeking to flip, but a sneeze can be cause by an adenovirus, which were apparently not suppressed this year as the influenza viruses and other four endemic coronaviruses were.

jMyles5• 5 years ago

It's more plausible, at least in my view, that this is the result of suppression of several endemic respiratory pathogens by viral interference (something that has been observed in previous pandemics).

https://medium.com/illumination-curated/the-unexpected-case-...

freeflight• 5 years ago

It's not just an anecdote, it's measurable on a global scale [0]

[0] https://www.nature.com/articles/d41586-020-03519-3

neither_color3• 5 years ago

Anecdotally I haven't had a cold in years. I work out 4 days a week and while I wouldn't call it a strict diet I have an upper limit calorie "budget" that I never exceed. While it's certainly possible that masks helped some people avoid all airborne transmissions last year, lots of people were also able to exercise more and make better food choices without the rush of breakfast and lunch commutes.

poutine2• 5 years ago

Get kids. They are plague carriers.

XorNot2• 5 years ago

I made absolutely no changes 1 year, but because my workspace at work was in an alcove next to an air conditioning vent that pulled air from the outside, I completely dodged the office cold because I basically had my own positive pressure environment.

It's more likely your lifestyle is simply keeping you away from people and places that experience high levels of foot traffic.

goatcode4• 5 years ago

got a cold

That's because the cold virus is spread by surfaces, and you likely touched something with it, then scratched your eyes. You can be 80 miles from someone, but if you touch something he touched, you're potentially getting his cold.

jMyles5• 5 years ago

That's because the cold virus is spread by surfaces

Stop. There is no one virus called "the cold virus", and several of the viruses that do cause colds (including, for example, the other four endemic coronaviruses) are not known to spread by fomites.

rootusrootus2• 5 years ago

It has been a pleasant year in that regard. We finally went on a domestic trip to Atlanta a couple weeks ago, after having been fully vaccinated in the middle of April. Guess what we came back with? A cold. Dammit!

listless• 5 years ago

Objectively, it doesn’t seem to matter if an area is masked or not. The virus won’t be stopped. Just compare Florida to California or Georgia to Washington state.

I know what the models say. But my eyes deceive me.

irq113• 5 years ago

Anecdotally, I spent an entire week, unmasked, in an apartment with someone sick with symptomatic Covid, and never caught it.

Anecdotes are not data.

AstralStorm• 5 years ago

As suspected, it's exactly a probability game. If there's few infectious particles sure to low concentrations (e.g. people distance or are outdoors), you would roll the 70% penetration chance fewer times, and result in very few particles reaching deeper into lungs too as the velocities are reduced.

When very close to an active particle source, you'd roll the conditional probability dice many more times.

The critical number is the base infectivity or viability. (CFU essentially) It is expected that sub-viable numbers might even work as a kind of vaccination if people isolate long enough. (stay at home for prolonged time without contact - scale of days at least)

epivosism3• 5 years ago

Yes. Crazy how hard it has been for people to get this:

Imagine a bulletproof vest with three larger-than-bullet-sized holes in it. Say you know someone is going to shoot ten bullets at you - would you not wear the vest because "the attack vector can fit through the pores"?

The point is people treat this as a binary 'safe' / 'not safe' switch, when actually risk is related to the distribution of exposure to dosage.

ppf• 5 years ago

If we're talking about the size of the holes in a mask compared to a virus, then it would be more like wearing a "bulletproof" vest full of holes 10x bigger than a bullet.

nradov2• 5 years ago

There is no evidence that inoculation with sub-viable numbers of virions works at all as a kind of vaccination. It's an interesting hypothesis but no one has done the human challenge trials necessary to test it.

tester756• 5 years ago

Aren't masks mostly/also about decreasing the area of the air that you pull in (closer to you, or in other words the distance from which you pull is smaller)?

like take a piece of paper in front of your face and breath with mask and without

AlexCoventry• 5 years ago

No. https://www.youtube.com/watch?v=0Tp0zB904Mc

cr18954• 5 years ago

Masks work by trapping particles exhaled or inhaled.

thewizardofaus• 5 years ago

Have any studies been completed yet on immune system efficiency/suppression after covid restrictions (masks, hand sanitizer etc) ?

In Australia we were very lucky with the COVID situation. And purely annecdotal, but I know many people who haven't been sick at all during the pandemic. But as we approach winter here and perhaps no longer hand sanitize appropriately, many of these people are becoming "the most unwell [they] have been in years".

deepserket• 5 years ago

protip: shower once a month to train your immune system during lockdown

astrange11• 5 years ago

I don't think it works that way. Your kids might develop some new allergies if you sanitize them too much, but just rub some dirt on your face or eat sauerkraut or something, it'll work out.

sschueller• 5 years ago

N95/FFP2 seem to be very effective.

I wish the media and government would have spent more time in educating people in things like how N95 masks work and that it isn't like a coffee filter. Even thought the pores are larger than a virus the masks are statically charged causes smaller things to get trapped. Many people don't know this but probably had an interaction with static electricity sometime in school and would understand it if someone explained it. Instead people get put in a bucket and no dialog is possible.

Education is key to understanding. You can't reach everyone most.

bitcurious• 5 years ago

I’m not sure there was any popular doubt over the efficacy of N95 masks. The problem was rather getting one - marketplaces like Amazon restricted access to masks if you weren’t affiliated with a hospital. So you were left with sketchy deals and weird vendor sites.

I suspect Amazon killed quite a few people over the last year by restricting access - supply scaled pretty quickly.

kickopotomus• 5 years ago

Unfortunately, a few of my friends fell victim to the Qanon conspiracy bandwagon and the fact that mask pore size is wider than the virus was heavily circulated as a reason for mask ineffectiveness.

viraptor2• 5 years ago

You could get halfway with other solutions. The 3-layer design with the synthetic layer in the middle tries to achieve the same idea. It's not going to be as effective as a certified N95, but it's better than a simple cloth. Not sure how common the idea was globally, but it was quite common to make them in Australia.

kadoban2• 5 years ago

Unfortunately there is _absolutely_ popular doubt about this, and every other thing you likely think is obvious about covid and the world. I don't think educating people about masks is really the answer though. I don't know what the answer is, or if there even is one. Feel like our society is coming apart at the seams.

tgsovlerkhgsel5• 5 years ago

The US seems to have relied heavily on cloth masks, even long after the shortages were over. From my understanding, surgical masks are much more effective (while often being more comfortable) than community/cloth masks. (I don't have a source for this on hand, but the German government did ban cloth masks/require at least surgical masks in many areas for this reason.)

I suspect a lot of that was out of a desire to not appear as backtracking on a previous position.

Laforet• 5 years ago

According to the data presented, surgical masks are still highly effective even after converting the scales to linear. Add social distancing on top, it is almost as good as N95.

And I very much doubt that N95 masks are effectively utilized by the general public considering how many poorly fitted masks I have seen over the past year.

Before the pandemic there had been several studies looking at the efficacy of N95 vs. surgical masks at preventing the transmission of influenza in hospitals. Most of them never got anywhere because it was soon realized that even doctors and nurses cannot be trusted to wear and change masks properly during the daily routine. Let's hope things have improved by now.

adrr2• 5 years ago

This was an education issue. There were KN95 and KF94 masks available for purchase. I bought KN95 masks off Amazon sold by Amazon proper and later switched to KF94 when they became widely available. Both masks have similar performance to N95. Someone of the KF94 masks i bought showed 99% filtering effectiveness in government testing.

matz12• 5 years ago

The problem is wearing mask is annoying and uncomfortable. If I have to choose, I'll choose the increased risk of covid all the time rather than wearing mask.

petertodd3• 5 years ago

A big part of why they are annoying and uncomfortable is the lack of one-way valves to make it easier to breath in them. In industry, when you actually need to wear a mask/respirator, they almost always have valves.

Unfortunately, we got stuck on the "wear masks to protect others" narrative, and people who actually were at risk were prevented from wearing much more effective, much more comfortable, masks that would actually work well at protecting them. Eg here in Canada, it's illegal to wear a mask/respirator with a valve on a plane.

neither_color3• 5 years ago

I'm my state we have a choice now and I still wear one most places except the gym. That's where my comfort vs risk threshold crosses. On that note one thing that's odd that I've observed in mixed mask rooms is that I don't like exposing my face to people who aren't exposing theirs. It's like my smile, a sign of peace, can't be reciprocated so I'm making myself vulnerable at their expense. I'll don a mask in mixed mask rooms not because of conformity per se, but what feels like defensiveness. My simian brain is thinking "you don't know if these are friendlies." I'm looking forward to any future psychological studies that explain this phenomenon.

mhb6• 5 years ago

I don't think people need to know how they work. They just need to know that those are what doctors wear and that they are very, very effective. And much better than a mask you make from ad hoc materials.

Once N95 masks became readily available and cheap, it was (and is) mysterious why people weren't being told to wear them to protect themselves instead of wearing whatever was at hand to sort of protect themselves and others.

mulmen• 5 years ago

If you tell me how something works and it fits within my mental model of the world then I will trust you. I will add this information to my mental model of the world.

If you tell me something works but can't explain how I will consider if the claim is worth evaluating then attempt to understand it myself before accepting it.

If you tell me to trust you with no explanation I will immediately distrust you.

auxym• 5 years ago

Last I checked in Canada, N95 masks are still about 3$ a pop for disposable, single use masks from industrial distributors. Pre pandemic, we bought 3M 8210s for about 15 cents in boxes of 160. I wouldn't call the current situation available and cheap.

Oh, and if you thought surgical masks were mildly uncomfortable, N95s are an order of magnitude worst. They pretty much need a perfect seal with your face and the 3Ms use a really tight rubber band to achieve that. 2 bands, actually.

I currently work on site and wear surgical masks all day, it's fine. Not sure I would want to do the same if it was N95s.

DanBC2• 5 years ago

Once N95 masks became readily available and cheap, it was (and is) mysterious why people weren't being told to wear them

Because they're difficult to wear. There are a bunch of photos on social media of HCPs who've got bruised faces after correctly wearing N95 / FPP3 for a day or two.

goatcode4• 5 years ago

The only time "N95" was uttered was last year, when we were being told: 1. Masks aren't needed; 2. Don't buy masks, healthcare workers need them.

It's unfortunate that we didn't go back to talking about proper masks before people started knitting them and making them out of rags and beads. One wonders what difference it might have made.

slver3• 5 years ago

Bless your soul, but what I've learned from the way we handled the pandemic worldwide (and are still handling it) is that information that's readily available and should in theory reach everyone, flows ridiculously slowly, even among specialists and political figures, it's easily corrupted and distorted, and a loud ignorant minority counts as much in the public discourse, as the voices of millions of reasonable people.

I'd say we have more evolving to do. Both biologically and socially. Individually (some) of us are relatively smart. Together we're as dumb as a piece of wood.

bellyfullofbac2• 5 years ago

Yeah, it's disappointing to see how I still see people wearing their masks incorrectly, e.g. just over the mouth and not covering their noses.

Sometimes I think human beings are advanced, but then I walk into a public toilet and I see evidence how many are still no better than animals. It's a simple technology, urinate into the hole where the water can wash it away and we'll remain hygienic, but a lot of people still fail at that.

ihsw• 5 years ago

I can't help but look at some peoples' rejection of public health guidance in the US as "not a bug/won't fix."

The relevant authorities (including traditional mainstream media) injected politics into the public discourse, which destroyed trust in what should be a normal public health process. Not only that but the relevant leaders of agencies decided to try manage the supply of masks through "steering" the public by downplaying the usefulness of masks.

Distrust of untrustworthy leaders is a feature, not a bug.

simpleguitar9• 5 years ago

Absolutely. Considering how long it took CDC and WHO to even acknowledge airborne transmission, even though the Chinese were very clear about it from very early on.

https://www.nytimes.com/2021/05/07/opinion/coronavirus-airbo...

LatteLazy• 5 years ago

I get where you are coming from but something I've learned from this pandemic is that "wear a mask" is too complex and burdensome for a significant proportion of people in the west...

Louis_Sarwal4• 5 years ago

We immediately face this issue: You should not act on information, or even knowledge. You should act on WISDOM. Wisdom is hard to gain, and yet it proves itself time after time to be better than the other forms of truth. Education is not the key; That would be wisdom. I do admit that most of what they teach is falsehood, and it would be better if it were truth.It would be better of there were no education at all than what we have now. In fact, it would be better to have no education system at all than to have a good education system that is liable to deteriorate. This is especially true when that system is a cost and a burden to and on society. Your information, however, is hardly better than the "n95 is coffee filter". There is no good proof on how airborne viruses are transmitted! Wearing a mask may do nothing, or it may do everything(Well, it can't do everything. Masks haven't stopped gov't from the vaccine)! It is likely that much of the transmission is not even caused by the oral and nasal areas, but instead is due to fecal aerosols. Our best solution may be the abolition of apartments and shared housing. SOme sort of filter should be put on the toilets, not on our faces. Cleansing chemicals(like bleach) should be put in the toilets, not in our arms.

Let us remember that choices should be made carefully, with consideration, and only once all of the facts are present.

Let us not be hasty-We must wait until a length of time has past in which effects which take alonger time to present themselves are presented.

This may require the foregoing of many necessary things. But such is the cost of life. Such is necessary to avoid death, or things much worse.

orf• 5 years ago

This comment is a pretty good argument for education reform, but likely not in the way you meant.

colonelanguz2• 5 years ago

You rock dude ignore these haters king

tzs• 5 years ago

Even thought the pores are larger than a virus the masks are statically charged causes smaller things to get trapped.

Even filters that aren't statically charged stop particles that are smaller than the gabs between the fibers. There are actually several mechanisms by which a filter can stop a particle.

1. Big particles don't fit between the fibers of the filter. Think fish in a fish net. This is called sieving.

2. Particles too small for sieving but heavier than the surrounding flow don't make the turns as well as the surrounding flow when the flow goes around the fibers. The particles can get embedded in the fibers. This mechanism is called inertial impaction.

3. The smallest might be too small to actually be affected much by the flow of the surrounding fluid through the filter. The move by diffusion, and many will randomly hit the fibers and get stuck.

4. Particles too big for diffusion but too light for inertial impaction still can run into fibers and get stuck. This is called interception.

5. As you mentioned, some filters have an electrostatic charge which can help trap particles.

The effectiveness of sieving, inertial impaction, and interception all follow S shaped curves that start out low for small particles, then at some point start rising, and then level out. The sieving curve's rise is almost vertical. The rise for inertial impaction is steep but not nearly as steep as it is for sieving. The curve for interception's rise is much more relaxed.

The effectiveness for diffusion goes the other way. Much more effective for very small particles, then above some size drops down and is low from then one.

When you put all these together, you get a curve that is effective at the small end, and at some point as size goes up effectiveness drops, reaching a minimum, and then rises again to reach high effectiveness for particles above some certain size.

The reason 0.3 microns is used for many HEPA filter ratings is that is in the middle of the low part of that U shaped curve, so when you get a filter that removes, say, 99.97% of 3 micro particles, it should actually do better for both larger and smaller particles.

Here's a document that has some diagrams explaining all this, and has some graphs of the efficiency curves for mechanisms #1-4. http://donaldsonaerospace-defense.com/library/files/document...

Consultant32452• 5 years ago

You are being very generous in assuming the people in charge want you to be educated. It seems to me they wanted you to run around with a (relatively) useless cloth mask so they could horde the most effective masks for themselves.

asabjorn14• 5 years ago

N95/FFP2 seem to be very effective.

Why does then the states with the highest mask use (CA, NYC) have much higher covid positive rates than states with some of the lowest mask use (Florida, NYC)?

Education is key to understanding. You can't reach everyone most.

N95 masks improperly used will hold covid for 24hrs and spread them by the incessant touching most people do of their masks before they touch other things.

Education only works if the means as deployed are likely to have a positive effect, such as surgeons in a strict hospital settings (where they are still used the wrong way as most people still touch the mask).

kelnos4• 5 years ago

Why does then the states with the highest mask use (CA, NYC) have much higher covid positive rates than states with some of the lowest mask use (Florida, NYC)?

They don't. Stop spreading misinformation. (Also I love that in this repeat of your misinformation, you accidentally typed "NYC" where you meant to say "Texas". And it would behoove you to learn the difference between a city and a state.)

chimprich7• 5 years ago

Why does then the states with the highest mask use (CA, NYC) have much higher covid positive rates than states with some of the lowest mask use (Florida, NYC)?

Even if that was true, places that were hit hardest by the pandemic tended to impose the most severe restrictions.

It's like finding that crash barriers are installed on roads with the highest accident rate and asking whether crash barriers are useless.

brobdingnagians3• 5 years ago

This isn't a study; it is a mathematical model [1].

Here, we develop a quantitative model of airborne virus exposure that can explain these contrasting results and provide a basis for quantifying the efficacy of face masks. We show that mask efficacy strongly depends on airborne virus abundance. Based on direct measurements of SARS-CoV-2 in air samples and population-level infection probabilities, we find that the virus abundance in most environments is sufficiently low for masks to be effective in reducing airborne transmission.

Meanwhile, they ignore the dozens of studies showing masks are ineffective, or even counterproductive:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4420971/

https://pubmed.ncbi.nlm.nih.gov/29395560/

https://pubmed.ncbi.nlm.nih.gov/32590322/

https://pubmed.ncbi.nlm.nih.gov/15340662/

https://pubmed.ncbi.nlm.nih.gov/26579222/

https://pubmed.ncbi.nlm.nih.gov/31159777/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5779801/

https://pubmed.ncbi.nlm.nih.gov/19216002/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4420971/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2493952/pdf/ann...

https://www.nap.edu/catalog/25776/rapid-expert-consultation-...

https://www.nap.edu/read/25776/chapter/1#6

https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6599448/

https://www.acpjournals.org/doi/10.7326/M20-1342

https://link.springer.com/article/10.1007/s00392-020-01704-y

dmead• 5 years ago

you really had that list ready to go...

chrischattin2• 5 years ago

Yeah, this right here. Masks efficacy for stopping viral transmission has been heavily studied. I could post literally hundreds more examples of statistically significant, RCT'd science showing they have no effect on viral transmission.

Wearing masks has never been about the science.

oasisbob3• 5 years ago

I could post literally hundreds more examples of statistically significant, RCT'd science showing they have no effect on viral transmission.

Please do. I'm only aware of about a half-dozen controlled trials of mask usage, and they're all low-powered.

oarfish• 5 years ago

Interesting how some of the linked studies either contradict your statement, or seem to have nothing to do with it.

brobdingnagians3• 5 years ago

Some are indirectly related, but all are linked in some way. Like how some find that it _could_ have a positive effect and postulate how, but that the studies they reviewed in the meta-review didn't _show_ that.

takeda2• 5 years ago

The study about mask being ineffective is about cloth mask. That's why the hospital masks are no longer made of cloth.

brobdingnagians3• 5 years ago

That is true; but a large number of people are walking around with cloth masks believing that they are helpful, while that study has shown them to potentially increase risk.

It did show "Penetration of cloth masks by particles was almost 97% and medical masks 44%." So that was a positive for medical masks. Though some of the other studies address how those need to be used properly and not re-used.

The main point is that, in general, media has not done a good job of transmitting studies on risk reduction; they've mainly done propaganda, which can do more harm by promoting things like cloth masks and not informing people about proper use of medical masks.

caddemon4• 5 years ago

That study also focuses on influenza which does not transmit quite the same way as COVID. A bunch of these links were the same thing being shared in the early days of COVID by doctors claiming that masks did not work. Obviously most healthcare organizations have changed their recommendations in light of new evidence specific to this pandemic.

microdrum2• 5 years ago

You are exactly correct, and being downvoted because of religious zealotry. This is a mathematical model. Yes, face coverings cover the face. It's a long (and ultimately disproven) leap to: face coverings materially suppress virus in a society of millions of people.

omegaworks2• 5 years ago

Half the articles on your list are tangential (masks make it marginally harder to exercise, ok duh). The article posted helps us understand why the viral concentration in the environment also impacts efficacy, it helps explain why some of the articles you posted see inconclusive results.

toss12• 5 years ago

And even the "masks make it marginally harder to exercise" is likely wrong.

The winner of the 10,000m race at the 2019 USA Track & Field Championships wore a mask against his pollen allergies. [1]

Worn properly, they just disappear. I wear N95s a work for many tasks, and they are mildly distracting for a few minutes, then I forget about them. Even more so now with wearing them for the pandemic.

Yes, education about masks could be a LOT better, but using that is more anti-mask FUD is borderline sociopathic.

[1] https://www.oregonlive.com/trackandfield/2011/06/galen_rupp_...

jmull• 5 years ago

You really hurt your credibility when the first link doesn’t support the argument you claim it does.

oasisbob3• 5 years ago

Here is a recent published review for those seeking a more comprehensive and complete evaluation of the literature:

Howard, Jeremy, et al. "An evidence review of face masks against COVID-19." Proceedings of the National Academy of Sciences 118.4 (2021).

https://www.pnas.org/content/118/4/e2014564118

irq113• 5 years ago

That is a joke of a “review”, and should never have been published.

Consider that it doesn’t mention the only randomized controlled trial of masks and Covid ever performed (it showed no significant protective effect), which was conducted during the period the “review” was being compiled:

https://www.acpjournals.org/doi/10.7326/m20-6817

There’s simply no excuse. the authors cherry-pick and misinterpret top-line data to craft a narrative. It’s not a review, it’s an editorial.

cataflam• 5 years ago

Meanwhile, they ignore the dozens of studies showing masks are ineffective, or even counterproductive

Let's try to figure out how well your summary is actually supported by your citations, especially as TFA is about medical masks and N95 masks and doesn't mention cloth masks.

TL;DR: It's not (and ignores the multiple studies showing surgical and N95 masks are effective to prevent SARS-CoV infections).

What your citations say is "cloth masks seem ineffective (but not surgical/N95), masks in general seem to protect less from influenza than coronaviruses, and wearing a mask may have some effect on exercise (although magnitude of the effect and consequences are unclear)". I wouldn't have had a problem with that statement. Whether that's the whole story or cherry-picking of studies is another question.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4420971/

(2015) Shows that cloth masks are less effective than medical masks... and incidentally that medical masks are effective. One study in, already contradicts your statement.

https://pubmed.ncbi.nlm.nih.gov/29395560/

(2017) Not about mask efficacy in disease prevention, but effects on exercise. No difference in distance, heart rate, O2 saturation, but 20% higher shortness of breath.

https://pubmed.ncbi.nlm.nih.gov/32590322/

(2020) Not about mask efficacy in disease prevention, but effects on exercise again. Also, not an experimental study but a comment/hypothesis.

https://pubmed.ncbi.nlm.nih.gov/15340662/

(2004) Not about mask efficacy in disease prevention, again. Study on patients with end-stage renal disease.

https://pubmed.ncbi.nlm.nih.gov/26579222/

(2015) Not about mask efficacy in disease prevention, again. Study on pregnant women.

https://pubmed.ncbi.nlm.nih.gov/31159777/

(2019) First interesting one. Show that viruses may deposit on the outer surface of medical masks. May prove useful in educating people to handle with care (although it seems that contamination by touching contaminated surfaces accounts for a negligible amount).

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5779801/

(2012) Ah, better. Review of a small number of other studies, focused on influenza and close contact with an infected patient. Does not conclude masks are ineffective, but more that good data and studies are hard to come by, that the studies they reviewed were between inconclusive and positive, and they may be protective when combined with other hygiene practices. Also notes that the studies on SARS coronavirus transmission found masks protective, but the results may or may not apply for influenza. It also notes compliance and correct usage are likely factors in reduced effectiveness.

So, while this is the closest so far to your assertion, it doesn't quite support it either. Annex 5 in particular shows that the SARS coronavirus studies reviewed seem to show a protective effect.

Much larger and wider reviews, that include this one, reach different conclusions for the topic at hand. See for example https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8084286/ and https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7718106/

https://pubmed.ncbi.nlm.nih.gov/19216002/

(2008) Lol. Study on 32 health-care workers, and the incidence of common cold. There was 1 cold in each group. Sample way too small to reach any conclusion, as they themselves conclude.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4420971/

Same article as the first one in the list.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2493952/pdf/ann...

(1981) Interesting, although a small trial study. But it only cares about a very specific thing: the efficiency of masks in surgery to avoid contaminating an open wound, unrelated to the airborne spread of respiratory diseases. More studies and reviews have followed, with mitigated results, see for example https://pubmed.ncbi.nlm.nih.gov/33039336/

Interesting but irrelevant for the topic at hand.

https://www.nap.edu/catalog/25776/rapid-expert-consultation-...

(2020) Expert consultation, limited to the effectiveness of homemade fabric masks. It says verbatim: "It does not apply to either N95 respirators or medical masks." (and it doesn't even conclude that homemade cloth masks are ineffective, only that more research is required).

https://www.nap.edu/read/25776/chapter/1#6

That's the same as the article just above. Could be the 2nd honest error of course, or could be a sign you've copy/pasted part or all of the list with little editing/proofreading.

https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article

(2020) Review of multiple measures against influenza contamination, that seems to show no effectiveness. The authors point out themselves the limitations of the study however, small sample size and compliance issues. It's an interesting data point, but it targets influenza and I wouldn't say it disproves masks effectiveness.

When looking at the bigger picture, and more and larger review, doesn't yield the same conclusions. See for example https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7718106/ that includes this study among those reviewed. Interestingly, it seems to show much more conclusive results for coronavirus infection prevention than influenza, and cautions against cloth masks.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6599448/

(2019) Physical study of filtering efficiency of cloth masks vs surgical masks, especially after washing

https://www.acpjournals.org/doi/10.7326/M20-1342

(2020) One of many physical studies on patients coughing in a petri dish with various mask types. Only 4 patients, and one of the only such physical studies I've seen that didn't show a significant effect.

https://link.springer.com/article/10.1007/s00392-020-01704-y

(2020) Another one that talks about exercise and not infection.

---

Looking in general at country-level data, using masks earlier seems to be significantly associated with lower mortality. See for example https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7695060/ for a wide study and https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7392429/ for a small comment

antattack• 5 years ago

Results only apply to indoor environment. Maybe source control could be extrapolated to outdoor conditions and close contact.

mrfusion• 5 years ago

Even if this is true, I still don’t think someone at high risk should be trusting their life to a piece of cloth.

pmoriarty• 5 years ago

"This is an open-access article distributed under the terms of the Creative Commons Attribution license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited."

So happy to see that.

anonymousiam• 5 years ago

Here's the manufacturer's (3M) label:

WARNING: This respirator helps protect against certain particulate contaminants but does not eliminate exposure to or the risk of contracting any disease or infection. Misuse may result in sickness or death. For proper use, see supervisor, or User Instructions.

https://multimedia.3m.com/mws/media/1837275O/3m-9132-healthc...

adrr2• 5 years ago

Because they are just NIOSHA certified and not FDA. Only certain N95s are have gone through testing and certification to be cleared for medical use.

userbinator• 5 years ago

That's standard legal ass-covering.

simpleguitar9• 5 years ago

Notice the word 'eliminate'.

Nobody could claim something would 'eliminate exposure or risk of contracting any disease' and not get sued immediately by someone who got sick.

In Wuhan, something like 10,000 doctors were sent in to treat the thousands in field hospitals. None of them caught covid during that time.

N95s work, if worn properly (and pass a fit test, even a crude one).

tgsovlerkhgsel5• 5 years ago

This entire study seems to be centered around a theoretical, mathematical model, and I didn't see any attempt to actually validate that model.

Basically, the authors seem to assume that the virus behaves according to their formulas, and show that under their assumptions, face masks work, but don't actually prove that their assumptions match reality - or did I miss something?

FiReaNG3L• 5 years ago

No you didn't miss anything - most people upvoting this didn't read anything more than the title.

omegaworks2• 5 years ago

It invites rigor in studying mask efficacy. Some studies out there show inconclusive results of mask usage, and this article helps give us an explanation as to why we might be seeing that. The model shows that in an extremely virus-rich environment masking can be rendered ineffective, but in virus-poor environments, even surgical masks decrease the probability of infection.

Researchers need to measure concentration of virus in the environment as well as mask usage to show the efficacy of masks in real world situations.

rsj_hn• 5 years ago

Indeed this is the money paragraph:

"The effectiveness of masks, however, is still under debate. Compared to N95/FFP2 respirators which have very low particle penetration rates (around ~5%), surgical and similar masks exhibit higher and more variable penetration rates (around ~30-70%) (2, 3). Given the large number of particles emitted upon respiration and especially upon sneezing or coughing (4), the number of respiratory particles that may penetrate masks is substantial, which is one of the main reasons leading to doubts about their efficacy in preventing infections. Moreover, randomized clinical trials show inconsistent or inconclusive results, with some studies reporting only a marginal benefit or no effect of mask use (5, 6). Thus, surgical and similar masks are often considered to be ineffective. On the other hand, observational data show that regions or facilities with a higher percentage of the population wearing masks have better control of the coronavirus disease 2019 (COVID-19) (7–9). So how to explain these contrasting results and apparent inconsistencies?

Here, we develop a quantitative model of airborne virus exposure that can explain these contrasting results and provide a basis for quantifying the efficacy of face masks. "

So they are left with a conundrum that places which use surgical masks seem to be better off, whereas randomized control studies of surgical masks show little to no benefit. This is what they try to explain with a mathematical model.

BugsJustFindMe• 5 years ago

The mistake that many people make, and that I think you're implicitly making here too, is this notion of "controlled study". If the study denies the result seen time and again in real life, perhaps the study isn't studying correctly.

function_seven4• 5 years ago

On the other hand, "observational data show that regions or facilities with a higher percentage of the population wearing masks have better control of the coronavirus disease 2019 (COVID-19) (7–9)." So how to explain these contrasting results and apparent inconsistencies?

My hypothesis regarding surgical mask prevalence and how it correlates with better virus control:

People who wear masks--however effective they may be--also behave in other ways to limit the spread. They minimize time spent in public indoor spaces, they keep distance from other people, they're more likely to self-quarantine if a family member is sick, etc.

The mask-wearing prevalence is a proxy for how serious the wearer takes Covid as a threat.

wrycoder• 5 years ago

I suspect that in locations with a higher prevalence of masking the population is generally more vigilant: more hand washing, more social distance, stay at home when ill, avoid obviously ill people, and so on. May be a case of correlation, not causation.

It would be interesting to have a trial where everyone was wearing N95s, but we're not likely to see that.

caddemon4• 5 years ago

The RCTs I have seen with basic surgical masks also seem to focus only on protection of the wearer, whereas on a societal level wearing even a shitty mask may be helping to prevent spread by presymptomatic people. I think it is unlikely the positive outcomes in mask wearing communities are purely due to confounders, although of course they probably also play a role.

tgsovlerkhgsel5• 5 years ago

What I don't understand... the UK was already doing challenge studies (intentionally infecting consenting volunteers).

Why didn't they make one with masks? Really can't be that hard to take a known infected person, sit them on a chair, arrange 100 people around them for a few hours with masks applied in a checkerboard pattern, and observe the results.

This is usually out of question for ethical reasons, but they already decided that that wasn't an obstacle, so why not (also) do a study on this?

(Or rather, arrange 10x 10 people, in 5 rounds putting a mask on the infected person.)

_Nat_2• 5 years ago

tl;dr- There wasn't really a conundrum to explain related to mask-effectiveness at different levels. Rather, it's more like a lack of good data, as prior studies being cited were ridiculously weak.

---

This seems like a largely helpful characterization.

However:

So they are left with a conundrum that places which use surgical masks seem to be better off, whereas randomized control studies of surgical masks show little to no benefit. This is what they try to explain with a mathematical model.

There wasn't really a conundrum. When the study writes:

Moreover, randomized clinical trials show inconsistent or inconclusive results, with some studies reporting only a marginal benefit or no effect of mask use (5, 6).

, the two studies they cite with inconclusive data are ridiculously weak.

The first one (their "5") is [https://academic.oup.com/jid/article/201/4/491/861190]. This was published in 2010, with data from 2006-to-2007, for "influenza-like illness" (not SARS-CoV-2, nor even influenza (explained below)). Apparently they asked students living in the dorms to do certain behaviors for weeks at a time. They concluded:

Conclusions: These findings suggest that face masks and hand hygiene may reduce respiratory illnesses in shared living settings and mitigate the impact of the influenza A(H1N1) pandemic.

And if that sounds inconclusive, yeah.. their study was ridiculously under-powered. In fact:

This study has several limitations. First, influenza incidence was low, so it is likely that most ILI cases were not associated with influenza infection, even though the study was conducted during the influenza season.

So not only were they not writing about COVID, apparently the authors argue that most of the cases probably weren't even influenza. There're other huge problems with this study too.

The second one (their "6") is [https://pubmed.ncbi.nlm.nih.gov/33205991/]. This study assigned subjects a recommendation to wear masks -- presumably some who were recommended to wear masks didn't, while some who weren't recommended to wear masks did.

Even then, their statistical analysis was very noisy:

Although the difference observed was not statistically significant, the 95% CIs are compatible with a 46% reduction to a 23% increase in infection.

And their stated limitations:

Limitation: Inconclusive results, missing data, variable adherence, patient-reported findings on home tests, no blinding, and no assessment of whether masks could decrease disease transmission from mask wearers to others.

Point being that there's not really a conundrum related to things not fitting together so much as a simple lack of good data.

panarky2• 5 years ago

The effectiveness of masks, however, is still under debate

Effective for the mask wearer, or effective for others in the vicinity of the mask wearer?

It's well established that cheap cloth masks and procedure masks don't protect the mask wearer very much.

The rationale for cheap masks is that they drastically reduce the spread of particles from the wearer to everyone else nearby.

If your goal is to protect yourself, wear an N95 or better.

If your goal is to protect a population, and N95s aren't available, then the cheap mask help a lot when people wear them.

jonplackett3• 5 years ago

I really don’t get why this is still considered a conundrum

Lots of places have R hovering around 1. If it goes to 1.1 everything goes to shit, if it drops to 0.9. Everything will be fine.

So even if masks reduce spread by a tiny amount, even 10% better. That could easily swing you below 1 and save the day.

andreygrehov2• 5 years ago

observational data show that regions or facilities with a higher percentage of the population wearing masks have better control of the coronavirus disease

Which is also not entirely true. There are quite a lot of regions (data from worldometer, statista) that have a better control of the virus despite people not giving a crap about face masks. For instance, Florida has 1600 deaths/M vs 3000 deaths/M in New Jersey. What'd be the explanation?

addicted• 5 years ago

Considering that the vast majority of cases of COVID are asymptomatic, it’s pretty apparent that the viral load needed to infect someone enough that they even exhibit symptoms, never mind need to be hospitalized, is not easy to achieve. As such, it’s likely even a 30% reduction (which is on the lower end of the range) in the viral load inhaled by someone could drastically reduce the chance of symptomatic COVID.

And when you combine 30% reductions for both the receiver and the emitter, it gets much higher.

raverbashing2• 5 years ago

Ah yes the "randomized controlled" studies 5 and 6.

5 is about influenza and 6 is not even worth the paper it's printed on.

No kidding, 6 is "recommending" people to wear a mask (and not even trying to control for the actual number).

So no, I have no qualms in calling study 6 useless, I've seen science fair projects with more scientific rigor and relevance than that.

admissionsguy2• 5 years ago

Working down from the conclusion to find the necessary assumptions is the standard approach to COVID-related questions.

nerdponx• 5 years ago

This is a valid way to do science.

"What assumptions are required to make this conclusion valid?"

If the assumptions turn out to be outlandish, then maybe we can't take the conclusion to be true.

Louis_Sarwal4• 5 years ago

Probably not. Most things like this are like this. There may indeed be some underlying proof, but they either can't or won't show it to you-if it exists. It is more likely that it does not. They start with their conclusion. They rarely commence an empirical study, because that might prove their prepared conclusion wrong! A model, which can be used in place of reality, is not reality, and never will be. GIGO. The model was tailored to match their wanted results, or more likely they made a bad model and tweaked it to gain desired results. This does not mean that masks are bad-it just means that the methods used are generally false. Properly gained empirical evidence should be used, and it even should not be trusted if it points to you doing something stupid-like wearing a tissue on your face all day.

neolog• 5 years ago

The paper is fine, the title is clickbait.

nimish3• 5 years ago

Nope. It's circular. We need actual tests in the wild, not models.

simpleguitar9• 5 years ago

During an interview with some of the doctors sent into Wuhan in their wave, they claimed none of the 10 thousand or so doctors sent in became infected. They used strict PPE protocol, including N95 masks.

Given what we know about the covid transmission now, it was absolutely the N95s that prevented these doctors from getting infected.

apatters• 5 years ago

My thinking has always been that of all the possible interventions to reduce viral spread, something like making people wear masks while grocery shopping has almost no negative side effects. Whereas closing the grocery store altogether has major negative side effects, like lost jobs and people not being able to buy groceries.

So I think the evidential bar for requiring masks should be pretty low (unless it is a special case, like making people wear masks when they're exercising likely has larger negative side effects). Who cares if it may not do much? The cost of doing it is so low.

Whereas the evidential bar for policies that do more collateral damage ought to be higher.

lixtra2• 5 years ago

If masks turn out to be ineffective, the cost of having them recommended is reduced reputation and authority.

Would you take security advice from Bruce Schneier after he proposed you to cover your keyboard in snakeoil because it might protect against computer viruses (and if not, there is not much damage)?

BurnGpuBurn• 5 years ago

You are correct, although I wouldn't call this a study. It's a science paper, yes, but it doesn't contain any new data that has been studied, just some fancy formulas and graphs and conjecture by a couple of people with a science degree.

collyw5• 5 years ago

This has been the case with all of the non-pharmaceutical measures imposed. The models say they work, but real world data doesn't show much correlation.

microdrum2• 5 years ago

A science study that only shows, as this one does, that face coverings cover the face is not very useful. The public policy piece is much more complex. High masking states did NOT do better on COVID than low masking states.

tgsovlerkhgsel5• 5 years ago

By what metric? By deaths per capita, my impression was the low masking states did worse, but I didn't rigorously check the data.

joshuaengler• 5 years ago

The VAST majority of mask wearing I have seen in California has been average cloth-covers. I have only seen a handful of people out of thousands actually wearing N95 masks, so perhaps N95 is highly effective at stopping viruses, but I see basically nobody wearing that. Stores, offices, buildings, all are completely fine with you wearing a bandana over your face. There is effectively no point in even mandating mask laws unless you actually mandate the TYPE of mask that must be used. The coffee filters people are wearing over their face will do close to nothing, if not even make everything worse for their own personal health (lung issues, bacterial infections, etc.)

jonas212• 5 years ago

I've never seen anyone wearing a coffee filter over their face. What are you talking about?

Grimm665• 5 years ago

I haven't either but I did have to drive several miles out of my way a few months ago to get coffee filters at the only store in the state that seemed to have them in stock. I was told during checkout people were buying them in bulk to use as masks.

omginternets2• 5 years ago

The coffee filters people are wearing over their face will do close to nothing

I'm not an expert, but I believe this is not quite accurate. As I understand it, even a piece of cloth helps prevent the spread of the virus to others. The mechanism is that the virus exits your nose/mouth in the form of macroscopic droplets that later break down into microscopic droplets a few inches from your face. A bandanna will catch the big droplets before they split apart.

jayd16• 5 years ago

Is there some global increase in lung issues (besides covid) or bacterial infections or something?

refurb• 5 years ago

The other thing to consider is fit. When I needed a mask for workplace safety, I had to get a fit test done - otherwise you leave massive gaps around the edge of the masks that lets unfiltered air in and out.

I think surgical masks do a good job in containing droplets from a cough or sneeze, but if there are airborne particles, I doubt they do much. A good fitting N95 probably helps in that department.

ekianjo• 5 years ago

So one can make a model out of thin air and not validate it, and then write a paper about it claiming to have the holy grail? That's Science in 2021?

logicchains3• 5 years ago

So one can make a model out of thin air and not validate it, and then write a paper about it claiming to have the holy grail?

That's Academic Finance in Forever.

unishark3• 5 years ago

Works best if it fits the bias/agenda of the journal editors. The better you do that, the more weaknesses they will forgive.

vondur• 5 years ago

I don't know. We had some of the highest mask wearing percentages in the country here in Southern California, yet some of the highest infection rates in the world. Something isn't adding up here. I'm guessing if everyone had N95 masks, we would have seen lower numbers however. I don't think the average cloth masks that people are wearing are very effective.

omginternets2• 5 years ago

Could it have to do with population density (perhaps even only in certain areas)? My reasoning is that you could have high transmission among the minority that doesn't wear masks, and that might suffice to make the absolute case-load quite high.

nostrebored3• 5 years ago

Counterpoint: Miami

astrange11• 5 years ago

In NYC the less dense areas had worse infections.

The problem in California might be crowding, ie it's not designed for the population density and so everyone has roommates or lives with an extended family. That would cause more indoor transmission, and I believe a lot of cases in CA were among working class people and Latinos.

AuryGlenz2• 5 years ago

Could it be that Southern California believes in masks too much? As in, they weren’t as cautious in other ways?

awb3• 5 years ago

I wonder how much super spreaders affect outbreaks.

Let’s say LA had 50 super spreaders vs. 25 in SF. I’d expect LA to have more than 2x the cases because of the exponential spread of the virus.

And I think the idea behind masks was not that they’re a cure, but a 2nd best option if the best option of social distancing isn’t possible.

And even if they’re 30% effective, the idea is to get R (the number of subsequent people an infected person goes on to infect) to go down. Because a 30% reduction in transmission has a huge effect over time, even if it’s not perfect.

froh• 5 years ago

super spreaders and super spreader events are key to transmission, like indoor singing hallelujah or indoor family gatherings happy birthday granny or schooling, Kindergarden, you get the gist...

indoor and speaking/singing is the key combination for aerosol based transmission.

cr18954• 5 years ago

Zeynep Tufecki described this phenomenon in the Atlantic, going into its overdispersed nature of spreading and how most infections don’t result in a spread to others, but some circumstances become super-spreading events with an outsize impact:

https://www.theatlantic.com/health/archive/2020/09/k-overloo...

bagacrap• 5 years ago

how do you measure mask wearing percentages? Socal seemed to have a lot of unmasked private gatherings throughout the pandemic. The draconian lockdown measures just pushed the spread underground.

stretchwithme• 5 years ago

If high resolution video is to be believed, masks reduce how many particles get into the air when we cough, sneeze or talk.

https://www.youtube.com/watch?v=H2azcn7MqOU

davidhyde• 5 years ago

For those of you who haven’t seen the slowmoguys video about talking with and without a mask this is good:

https://youtu.be/gZ66wJFD3bs

If you want to skip the technical lighting bits then jump to the 4 minute mark. It’s difficult to argue against footage like that and it makes you wonder why some people take off their masks to talk.

perryizgr83• 5 years ago

wonder why some people take off their masks to talk.

Because voice is muffled by the mask and makes it very hard to understand in some cases. Taking off the mask is not acceptable, but it is not an unjustified response.

sjg007• 5 years ago

We know masks work for infection control which is why they are used in hospitals and also in clean room style manufacturing.

beagle39• 5 years ago

Bacteria and viruses behave differently. It’s possible, even likely, that a measure against one will be ineffective against the other.

In an attempt to fights a specific virus, namely sarscov2 - no, we don’t know that masks work. The cdc numbers I saw talk about 2% reduction in vivo.

xbar• 5 years ago

I was very happy to see "aerosols are physically defined as airborne solid or liquid particles with diameters smaller than 100 μm" as opposed to the bad 5 μm definition that caused so much trouble.

avereveard2• 5 years ago

"in our specific model which we specifically created around the exact conditions required for them to work"

vondro• 5 years ago

In Japan, people that are sick wear masks, voluntarily, not to spread the infection. Well, that was my observation travelling Japan, anyway. I was amazed by it, and as the pandemic started last year, I had hopes that this thoughtful behavior will become a norm in my area too (central Europe).

Unfortunately, it seems that will not be the case. Masks are universally hated.

adrianb• 5 years ago

Wearing masks when sick is a good hygiene practice in general. But in COVID context with significant asymptomatic spread it won't help as much as it does for colds and flu.

teleforce3• 5 years ago

Obligatory story on Manchurian plague epidemic regarding how surgical mask come to be a standard requirement during the treatment of any airborne disease [1][2].

Mind you that the original surgical mask was not invented for surgery, it was invented for the treatment of patients with airborne virus. Heck, every.single.time you meets someone who are skeptical about the effectiveness of the mask in mitigating the airborne virus transmission, just send them this story [1][2].

It also interesting to note that the inventor of the surgical mask Dr. Wu, (the doctor mentioned in the article) is not even the resident of Imperial China at the time, even though he is the first Chinese medical doctor trained and graduated from the University of Cambridge. The last Empire of China or Qing dynasty who was originally come from Manchuria, had to hire the best medical doctor that they can find in order the save the citizens native of Manchuria, from the raging epidemic. Dr. Wu has come very close to get the Noble price in medicine back in 1935 due to his novel surgical mask invention.

[1]https://insightplus.mja.com.au/2020/15/dr-wu-lien-teh-hero-o...

[2]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4291938/

incrudible3• 5 years ago

The Wu Lien-Teh mask is the precursor of KN95 masks, not surgical masks. See this:

https://de.m.wikipedia.org/wiki/Datei:How_the_gauze-cotton_m...

Surgical masks offer virtually no (personal) protection against airborne disease and fulfill a completely different purpose.

teleforce3• 5 years ago

Based on the design and capability, I doubt Dr Wu original mask back in the pandemic was even close to N95 mask in filtering the air probably closer to the surgical mask of today, if not worst. The N95 as we know today was invented just recently in 1995[1]. Even with its rudimentary design, Dr Wu's mask had managed to save many lives back then, and in my opinion surgical mask of today will be similar if not better than the original Dr. Wu's mask design.

[1]https://en.wikipedia.org/wiki/N95_respirator

incrudible3• 5 years ago

...in hamsters? In mice?

No, in a mathematical model - the gold standard of junk science.

Kurtose• 5 years ago

Anecdata from a _very_ frequent flyer: Naomi Campbell’s Airport Routine (2019). Makes sense to me.

https://youtu.be/b-U_jT9qWvs

egberts• 5 years ago

“... is still under debate ...” - NEXT!

domano• 5 years ago

We are in pandemic-mode for over a year now - isn't it obvious that masks help by now?

collyw5• 5 years ago

Doesn't seem to have been effective here, we have had to wear them including outdoors since October. But give me some model over real world data to convince me.

rdmirza• 5 years ago

I did not bother to read this thread in its entirety though I typically enjoy HN discussion.

Undoubtedly, masks of any quality work. Airborne viruses still exist in secretions (likely, in much higher concentrations). Secretions sometimes even carry living cells, would you imagine (in fact the #1 cause of sputum sample contamination for C&S; the bane of internists everywhere). High velocity events certainly increase the environment-load of secretion and thereby virus.

You don't need evidence in all cases. Im sorry to say, to the otherwise curious-minded, this is one of those cases.

Face masks effectively limit the probability of SARS-CoV-2 transmission

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