Counterquestion: Will presence of this evidence modify your position?
Can you see how the study you presented doesn't answer parent post's question?
Further, your study tests the first breath exhalation.
> We screened 3,363 individuals in two study phases, ultimately enrolling 246 individuals who provided exhaled breath samples (Extended Data Fig. 1). Among these 246 participants, 122 (50%) participants were randomized to not wearing a face mask during the first exhaled breath collection and 124 (50%) participants were randomized to wearing a face mask. Overall, 49 (20%) voluntarily provided a second exhaled breath collection of the alternate type.
So, your test says "when you put on a mask that mask will, immediately after you put it on, stop your exhaled breath hitting a plate placed in front of your mouth".
It says nothing about how effective that mask is over time.
Edit: Also that is for surgical face masks, most people just put a piece of cloth in their face. I would like to see a study for a piece of cloth in front of your mouth for the entire day and see how much virus there is after that.
They actually tested infected patients with and without mask.
This study is incredibly small, and operating on the limits of significance. Its hardly conclusive, and was done under fairly extreme conditions (30 mins in close proximity) compared to the scenarios in which masks are mandated today. The authors even mention that, for those who did not cough, no detectable virus was identified regardless of whether a mask was worn. Considering that the point of mandatory masking is to prevent asymptomatic transmission from brief interactions with strangers, I just don't find this study very convincing as a scientific basis for a mask mandate.
The study you linked did not have any covid patients.
> slows the spread of COVID-19 or a similar respiratory disease
What makes you believe that COVID-19 is spread significantly differently that the inconvenience of having to wear a mask is not bearable relative to the potential benefits? Do you believe that masks have risks other than being inconvenient?
All the things that happen in daily life rather than in a medical setting. Which is why despite full mask protocols and sanitiser at the door to every classroom kids going back to school this week around here have all have gone down with viral sore throats and noses.
That shouldn’t have happened if masks do what it says on the tin.
Unfortunately network effects dominate. We are not hamsters living permanently in cages.
We don't know, we don't have much evidence either way.
> but not stopping spread over the population?
Where do people wear masks? They wear masks when leaving their homes. Some of those journeys are essential, but a lot of them are not.
People have chosen something (mask wearing) that has at best weak evidence over something (physical distancing) that has much stronger evidence.
Most recommendations I've seen are to do both.
https://www.stripes.com/polopoly_fs/1.635444.1593270228!/ima...
They might have done so even without masks, it is hard to say, but it is pretty easy for people to think that it is fine to not keep distance when they have masks.
Here's a recent, high quality, paper in a high impact paper.
https://www.thelancet.com/journals/lancet/article/PIIS0140-6...
> Although direct evidence is limited, the optimum use of face masks, in particular N95 or similar respirators in health-care settings and 12–16-layer cotton or surgical masks in the community, could depend on contextual factors; action is needed at all levels to address the paucity of better evidence. Eye protection might provide additional benefits. Globally collaborative and well conducted studies, including randomised trials, of different personal protective strategies are needed regardless of the challenges, but this systematic appraisal of currently best available evidence could be considered to inform interim guidance.
There's a bit to unpack here.
1) I don't know anyone wearing a 12 to 16 layer cotton mask. At best they're wearing 4 to 6 layers of cotton. Most people have maybe two layer masks.
2) "paucity of better evidence" isn't how I'd describe something that has great evidence.
Look at how that paper describes the evidence for distancing vs masking:
> Our search identified 172 observational studies across 16 countries and six continents, with no randomised controlled trials and 44 relevant comparative studies in health-care and non-health-care settings (n=25 697 patients). Transmission of viruses was lower with physical distancing of 1 m or more, compared with a distance of less than 1 m (n=10 736, pooled adjusted odds ratio [aOR] 0·18, 95% CI 0·09 to 0·38; risk difference [RD] −10·2%, 95% CI −11·5 to −7·5; moderate certainty); protection was increased as distance was lengthened (change in relative risk [RR] 2·02 per m; pinteraction=0·041; moderate certainty). Face mask use could result in a large reduction in risk of infection (n=2647; aOR 0·15, 95% CI 0·07 to 0·34, RD −14·3%, −15·9 to −10·7; low certainty), with stronger associations with N95 or similar respirators compared with disposable surgical masks or similar (eg, reusable 12–16-layer cotton masks; pinteraction=0·090; posterior probability >95%, low certainty).
All of the mask evidence says "low certainty". That's from GRADE, and it means "low certainty (our confidence in the effect estimate is limited; the true effect could be substantially different from the estimate of the effect);"
Does it influence your position on whether or not masks are useful?
Parent poster isn't asking whether masks trap particles or not (clearly, they do), they're asking a much more interesting and useful question which is if we make everyone wear a mask does that prevent the spread of disease or not?
So far, we really don't have much evidence. In this thread, where lots of people are posting links, there's only one decent link posted by gameswithgo here:
The debate reminds me of the debate about smoking.
For a long time, smoking "probably" caused cancer. Meaning, almost certainly. There was plenty of evidence.
But for a long time, cigarette companies said it wasn't "proven" that it caused cancer. Meaning, let's carry on selling, advertising, consuming it in large quantities.
It would take a few more decades to reach the standard of "proof".
So smoking continued, people died.
Rather than following rational life-optimising behaviour based on the growing body of data.
As you illustrated in your example, the medical establishment is often disastrously wrong, so why shouldn't we take their recommendations with a grain of salt?
They have to take a little care where they swing their arms.
In fact some people don't take that much care, and we usually say it is the people who physically dominate a space by being inconsiderate of others who are acting entitled and privileged.
So no, I don't think it's entitled or privileged to ask people to reduce significant[+] aggregate harm to others, at minor inconvenience to themselves.
However, I think it's entitled and privileged for people to decide that they don't have to wear a mask based on their "personal risk assessment for themselves", on the theory that other people can just quit their jobs or whatever and stay locked up at home to feel safe from the unmasked crowds outside. That's the "if people want to feel safe they can stay at home if they want" theory. That's not a reasonable imposition, and does not constitute the reasonable balance of needs that we'd call a free society.
For those for whom it's particularly uncomfortable, I don't know the policy elsewhere, but in the UK, it's permitted to not wear a mask if you have a reason for not wearing one. Reasons are quite reasonable: For example if you're with someone who lip reads, or they give you anxiety or whatever.
The goal is to ensure that almost all people wear one, not that every last person must wear one if they have a reasonable reason not to.
The reason for enforced policy is because too many people won't wear one at all without a stronger incentive. Just asking people to not harm others isn't enough, it seems. (And people really can't get their intuitions around exponential growth and clustering, so they mis-estimate aggregate risks to others by a lot, even when they have numbers to go on.)
[+] (It affects the R number. The difference between R > 1 and R < 1 is pandemic versus disease dying out. It's also the difference between a long pandemic with onerous economic and social consequences, and something that is manageable. The overall effect is profoundly significant in aggregate.)
The problem with that framing is that most people quickly drop the "asymptomatic" bit, and so now we have people with symptoms going shopping wearing a mask. That mask isn't going to do much to protect other people, especially when you consider it's likely to be 2 layers of cotton, poorly fitted, with poor hand hygiene.
> The difference in conclusions of mask effectiveness studies is mainly due to different study contents, study designs, evaluation methods and endpoints. Understandably, good evidence on this topic is difficult to assess.
But the study's support for masks is crystal clear and you can't read the entire study (or even the abstract) and come away without that conclusion.
The more I engage with you the more I fear that you are not debating the subject in good faith.
> However, in many western advanced economies, those wearing masks are often met with suspicion in public, even causing panic in certain situation.
Really? Citation needed.
> Although the 1918 Pandemic (H1N1 virus) caused an estimated 40–50 million deaths worldwide, many still may view personal protective equipment (PPE) and physical barrier including wearing the mask as contrary to freedom and individualism.
Non-sequitur alert! Number one, PPEs themselves are value-neutral; it's the mandate that contrary to liberty as enshrined in the Constitution (you know, the highest law in the land). Number two, mask mandates can be both effective in slowing viral spread AND "contrary to freedom and individualism;" the two concepts are orthogonal. Most people understand this, but differ in prioritizing one over the other. The author seems to suggest that the two cannot be believed at once!
Are we all supposed to just take it for granted that masks would have helped in a situation that took place over 100 years ago before so many other medical advances? I don't think that's a fair assumption at all. If so, we could just invoke the Spanish Flu as evidence for any medical intervention we desire.
Omissions like these make it hard for me to take this study as authoritative about anything, especially when they themselves admit that the evidence on universal masking is contradictory.
If mask mandates slow the growth of asymptomatic cases, the R number must be lower.
As we all should know by now, reducing R is a good target, as the difference between R > 1 and R < 1 is profound, and R is thought to be close enough to 1 that measures taking place can make that difference.
This is very useful from a health perspective.
Thank you for the link.
Summary: "investigators found that the prevalence of COVID-19 antibodies among hospital employees was lower than what had been reported for the surrounding general community that is consistent with personal protective equipment being effective at preventing exposure of hospital workers. In addition, researchers found via laboratory testing that N95 masks with intact elastic straps or if sterilized maintained their effectiveness even if they had passed their expiration point, offering alternatives to the scarcity of N95 masks."
Conclusion: "PPE, when available and properly used, confers protection and lower infection rates of COVID-19 among health care workers when compared with reported infection rates in the general public."
Not a great start
This piece, which you present as good quality evidence, says
> The lack of clear recommendations for the general public and low uptake of wearing face masks and coverings may be attributed to: (i) over-reliance on an evidence-based medicine approach and assertion that evidence was weak due to few conclusive RCT (randomised controlled trial) results in community settings, discounting high quality non-RCT evidence.
Someone asks for good quality evidence and you post a link to an opinion piece saying stop over-relying on good quality evidence?
I mean, your link even says they don't have much evidence
> Current knowledge on the effectiveness of face masks to prevent virus transmission from COVID-19, SARS, MERS and H1N1 is mostly limited to studies of surgical masks and N95 respirators. The majority of existing studies are conducted in health care settings and focus on protection of the mask wearer as opposed to wearing a mask for the protection of others. This distinction is vital since mask wearing for the general public occurs in non-clinical situations (home, public transport, shops, restaurants) and involves both protection of oneself but also others.
[...]
> We emphasise that the majority of studies have been conducted in health care settings and there are therefore caveats in the ability to transfer results directly to community settings