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Effectiveness of Face Masks


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Masks are all the rage these days...but it may be that they are more effective at restoring public confidence during a pandemic than they are at actually protecting anyone from infection.

 

An interesting paper, written well before COVID.

 

Between 2004 and 2016 at least a dozen research or review articles have been published on the inadequacies of face masks. 5,6,11,17,19,20,21,25,26,27,28,31 All agree that the poor facial fit and limited filtration characteristics of face masks make them unable to prevent the wearer inhaling airborne particles. In their well-referenced 2011 article on respiratory protection for healthcare workers, Drs. Harriman and Brosseau conclude that, “facemasks will not protect against the inhalation of aerosols.” 11 Following their 2015 literature review, Dr. Zhou and colleagues stated, “There is a lack of substantiated evidence to support claims that facemasks protect either patient or surgeon from infectious contamination.” 25 In the same year Dr. R. MacIntyre noted that randomized controlled trials of facemasks failed to prove their efficacy. 

 

In 2015, Dr. Leonie Walker, Principal Researcher of the New Zealand Nurses Organization succinctly described- within a historical context – the inadequacies of facemasks, “Health care workers have long relied heavily on surgical masks to provide protection against influenza and other infections. Yet there are no convincing scientific data that support the effectiveness of masks for respiratory protection. The masks we use are not designed for such purposes, and when tested, they have proved to vary widely in filtration capability, allowing penetration of aerosol particles ranging from four to 90%.”

 

Why Face Masks Don't Work

 

Note: It is interesting that the internet is being "scrubbed" of articles like this one that question the efficacy of masks for infection control. If you go to the live version of the above link, you get this placeholder:

 

Scrubbed Page

 

I'm not sure why a well referenced paper written in 2016 is "no longer relevant" but fortunately the Wayback machine doesn't forget.

 

 

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http://m.nautil.us/issue/90/something-green/the-importance-of-face-masks-and-the-tragedy-of-downplaying-them

This is about risk management. The Swiss Cheese Model is often used in aviation. For an accident to happen, all the holes in the barriers have to align.   Conversely. The more barriers you h

That study had symptomatic patients forcefully cough into a petri dish through their mask.   The authors even admit it's not a great measure of whether or not it has much bearing on reducing

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And at the end of the day, cloth masks in my opinion don’t work in any form. They aren’t very good at source control, except for maybe very large particles.

 

I’m seeing more and more people now wearing cloth masks on the streets. And I don’t go to stores anymore, but my understanding is they’re wearing them there as well. I don’t have a problem with people wearing them. I just want them to understand that they aren’t very much more protective than if they weren’t wearing them. And they’re really not doing a whole lot of good for the people around them. So, we should continue to do social distancing as much as we possibly can. 

 

Interview in Infection Control Today with Dr. Lisa Brosseau, industrial hygiene and respiratory protection specialist, professor of environmental and occupational health science at the University of Illinois, Chicago

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  • 2 weeks later...

I didn't initially understand the broad recommendation to wear masks at first.

 

As the articles above demonstrate, the science doesn't support their effectiveness in preventing transfer, specifically in the case of this virus. There are piles of other studies that confirm that surgical masks, nevermind a bandana or "cotton face covering" are generally ineffective at protecting against an airborne virus, and there is a concern that they might actually produce a false sense of confidence....and then BOOM I understood why we are all wearing masks...

 

This is a form of security theater like the tamper seal on your vitamin bottle or the overworked, underpaid, unarmed TSA agent at the airport...the tamper seals were introduced in the wake of the 1982 Tylenol poisonings in order to restore public confidence in OTC medical products and the TSA was introduced to restore public confidence in air travel after the WTC attacks in 2001...both are apparently rather easy to defeat but they are part of what's known as "security theater" an elaborate Kabuki production intended to convey a sense of safety where one probably doesn't really exist.

 

Mask wearing, in this case, is no different. The CDC and all of the state health agencies are recommending that we cover our face, not because any of them seriously think they are effective at reducing viral spread, but in order to restore our confidence in being out in society again with other people.

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On 5/28/2020 at 7:40 AM, STENDEC said:

As the articles above demonstrate, the science doesn't support their effectiveness in preventing transfer, specifically in the case of this virus.

That study had symptomatic patients forcefully cough into a petri dish through their mask.

 

The authors even admit it's not a great measure of whether or not it has much bearing on reducing transmission among asymptomatic people under normal daily activities. If the masks reduce transmission of viral droplets or reduce the distance that droplets travel after exhalation, they're going to bring R0 down.

 

If we set the bar so high that only a perfect mask is acceptable (prevent infected, symptomatic patient from contaminating a petri dish with multiple active coughs directed at said petri dish) then we're going to miss a whole range of interventions that can significantly reduce the R0, or even reduce the viral load of those who are exposed.

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On 5/30/2020 at 12:57 AM, Construct said:

The authors even admit it's not a great measure of whether or not it has much bearing on reducing transmission among asymptomatic people under normal daily activities.

 

This is true.

 

However, the first post in this thread had an article with a dozen or so references indicating that actual surgical face masks are generally of little value in preventing viral transmission even when used by professionals in medical settings...I have to believe that the cotton home-made masks worn by the general public are probably even less so.

 

The second post contains an interview with a widely cited expert in respiratory protection on the utility of mask-wearing. Her conclusion, repeated here is:

 

"I just want [people who are wearing masks] to understand that [masks] aren’t very much more protective than if they weren’t wearing them. And they’re really not doing a whole lot of good for the people around them."

 

OSHA also provides the following guidance on surgical masks...note these are typically made of melt-blown, non-woven material that is electrostatically charged to improve the capacity to capture small particles....this is not talking  about a homemade mask that someone sewed out of a cotton tshirt or a bandana. (emphasis mine)

 

Surgical masks are used as a physical barrier to protect the user from hazards, such as splashes of large droplets of blood or body fluids. Surgical masks also protect other people against infection from the person wearing the surgical mask. Such masks trap large particles of body fluids that may contain bacteria or viruses expelled by the wearer.

 

Surgical masks are not designed or certified to prevent the inhalation of small airborne contaminants. These particles are not visible to the naked eye but may still be capable of causing infection. Surgical masks are not designed to seal tightly against the user’s face. During inhalation, much of the potentially contaminated air can pass through gaps between the face and the surgical mask and not be pulled through the filter material of the mask. Their ability to filter small particles varies significantly based upon the type of material used to make the surgical mask, so they cannot be relied upon to protect workers against airborne infectious agents

 

source

 

Data indicates that the virus that causes COVID19 is widely distributed in both droplets and airborne aerosols, even by patients wearing masks.

 

Even the US CDC, the agency recommending "cloth face coverings" as a response to COVID19, has the following to say about surgical masks, which again, are presumably more effective than a single-ply cloth face covering :

 

Surgical masks, on the other hand, are not specifically designed to protect the wearer from airborne hazards. These devices limit the spread of infectious particles expelled by the wearer. They are used to help protect a sterile field, such as the area surrounding the site of a surgical incision, from contamination by particles expelled by the wearer, such as those generated by coughs or sneezes. Surgical masks also help provide a physical barrier to protect the wearer from splashes, sprays, or contact with contaminated hands. The Food and Drug Administration (FDA) regulates surgical masks. The FDA regulations do not require surgical masks to form a seal against the user’s face or to have a level of filtration that provides the user protection from aerosol exposures.

 

source

 

 

So do masks make viral transmission more likely? Probably not.

 

Do they catch large droplets expelled from someone sneezing or coughing? Almost certainly.

 

Do they prevent people from touching their face with their hands? Maybe....some people seem to touch their faces more when wearing a mask in order to adjust the fit.

 

Do they prevent an asymptomatic person from exhaling aerosolized viral particles into the air around him or other people from breathing in the same particles breathed out by others? IOW, do they protect me from you or you from me if neither of us is coughing or sneezing? No.

 

Do they make the average person, the one who has a very small chance of catching this virus in the first place, and an even smaller chance of becoming seriously ill from it, more confident about going back to work and going to Walmart and spending money? Absolutely.

 

So masks are a very useful tool in the management of this pandemic...just not for the reasons most people think.

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It looks like cloth face masks probably do almost nothing to prevent infection...reducing viral penetration only by about 3% 

 

The rates of all infection outcomes were highest in the cloth mask arm, with the rate of ILI statistically significantly higher in the cloth mask arm (relative risk (RR)=13.00, 95% CI 1.69 to 100.07) compared with the medical mask arm. Cloth masks also had significantly higher rates of ILI compared with the control arm. An analysis by mask use showed ILI (RR=6.64, 95% CI 1.45 to 28.65) and laboratory-confirmed virus (RR=1.72, 95% CI 1.01 to 2.94) were significantly higher in the cloth masks group compared with the medical masks group. Penetration of cloth masks by particles was almost 97% and medical masks 44%.

 

 Moisture retention, reuse of cloth masks and poor filtration may result in increased risk of infection.

 

BMJ Study

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Based on the RCTs we would conclude that wearing facemasks can be very slightly protective against primary infection from casual community contact, and modestly protective against household infections when both infected and uninfected members wear facemasks. However, the RCTs often suffered from poor compliance and controls using facemasks. Across observational studies the evidence in favour of wearing facemasks was stronger. We expect RCTs to under-estimate the protective effect and observational studies to exaggerate it. The evidence is not sufficiently strong to support widespread use of facemasks as a protective measure against COVID-19.

 

Preprint Systemic Review Study

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And then there is this robust bit of "science" that made headlines today.

 

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). Eye protection also was associated with less infection (n=3713; aOR 0·22, 95% CI 0·12 to 0·39, RD −10·6%, 95% CI −12·5 to −7·7; low certainty). Unadjusted studies and subgroup and sensitivity analyses showed similar findings.

 

Lancet Study

 

So let's see...they lumped effectiveness studies of fitted N95 respirators in with studies of surgical and cloth masks....although multi-ply 12-16 layer masks rather unlike the single-ply models that most people are wearing around...I can't imagine how those results might be at all misleading....

 

And then their exhaustive review of the available literature was unable to turn up any randomized controlled trials like this one, and this one and finally this one (repeated from above) which indicated that the use of a cloth mask resulted in a 72% higher infection rate when compared to wearing a surgical mask and led the authors to conclude:

 

"This study is the first RCT of cloth masks, and the results caution against the use of cloth masks. This is an important finding to inform occupational health and safety. Moisture retention, reuse of cloth masks and poor filtration may result in increased risk of infection."

 

 

So watch out for publishing bias, keep your distance, the further apart the better, wear goggles apparently, and if you are going to wear a mask, don't wear a cloth one.

 

 

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These guys were a little kinder than I was about the recent meta-analysis but why, oh why, can't the rest of the news coverage of COVID be even this evenhanded?

 

What's the best way to protect yourself when you're at risk of exposure to SARS-CoV-2? It seems like a simple question, but many of the options—face masks, lockdowns, social distancing, etc.—have been politically controversial. In addition, it has been difficult for public health authorities to maintain a consistent message, given our changing state of knowledge and their need to balance things like maintaining supplies of protective equipment for health care workers.

 

But several months into the pandemic, we've started to get a clear indication that social isolation rules are helping, providing support for those policies. So, where do we stand on the use of masks?

 

Two recent events hint at where the evidence is running. The first involves the retraction of a paper that appeared to show that mask use was ineffective. And the second is a meta-analysis of all recent studies on the use of protective gear against SARS-CoV-2 and its relatives SARS and MERS. It finds support for a protective effect of masks—as well as eye protection—although the underlying evidence isn't as strong as we might like.

 

Ars Technica Article

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On 6/2/2020 at 6:14 PM, STENDEC said:

if you are going to wear a mask, don't wear a cloth one.

 

But if you insist on wearing a cloth mask, every time you wash, dry and reuse it, you make it more ineffective than when it was new.

 

Unlike the disposable surgical masks, cloth masks are often washed and dried repeatedly and used for a prolonged period of time. However, the study on the microscopic structure of the cloth masks showed that repeated washing and drying may reduce the quality of the cloth mask, by almost 20% after four such cycles. In the light of this evidence, it may be advisable to change the cloth masks regularly rather than repeated washing.

 

Article

 

 

 

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  • 2 weeks later...

We know that wearing a mask outside health care facilities offers little, if any, protection from infection. Public health authorities define a significant exposure to Covid-19 as face-to-face contact within 6 feet with a patient with symptomatic Covid-19 that is sustained for at least a few minutes (and some say more than 10 minutes or even 30 minutes). The chance of catching Covid-19 from a passing interaction in a public space is therefore minimal. In many cases, the desire for widespread masking is a reflexive reaction to anxiety over the pandemic.

....

Masks are not only tools, they are also talismans that may help increase health care workers’ perceived sense of safety, well-being, and trust in their hospitals. Although such reactions may not be strictly logical, we are all subject to fear and anxiety, especially during times of crisis. One might argue that fear and anxiety are better countered with data and education than with a marginally beneficial mask, particularly in light of the worldwide mask shortage, but it is difficult to get clinicians to hear this message in the heat of the current crisis. Expanded masking protocols’ greatest contribution may be to reduce the transmission of anxiety, over and above whatever role they may play in reducing transmission of Covid-19.

 

NEJM Article

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  • 3 weeks later...

Even the WHO is pretty equivocal in the effectiveness of cloth masks worn by the public.

 

The use of masks made of other materials (e.g., cotton fabric), also known as nonmedical masks, in the community setting has not been well evaluated. There is no current evidence to make a recommendation for or against their use in this setting.

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15 hours ago, STENDEC said:

Even the WHO is pretty equivocal in the effectiveness of cloth masks worn by the public.

 

The use of masks made of other materials (e.g., cotton fabric), also known as nonmedical masks, in the community setting has not been well evaluated. There is no current evidence to make a recommendation for or against their use in this setting.

 

In fact, this has the full report. The previous one was a summary: https://www.who.int/publications/i/item/advice-on-the-use-of-masks-in-the-community-during-home-care-and-in-healthcare-settings-in-the-context-of-the-novel-coronavirus-(2019-ncov)-outbreak

 

The evidence is low quality, and the WHO gives a weak recommendation ( encourage) and leaves it up to different countries. I think this is a case where political pressures is also playing a role in making recommendations. 


" Advice to decision makers on the use of masks for the general public

 

Many countries have recommended the use of fabric masks/face coverings for the general public. At the present time, the widespread use of masks by healthy people in the community setting is not yet supported by high quality or direct scientific evidence and there are potential benefits and harms to consider (see below).


"However, taking into account the available studies evaluating pre- and asymptomatic transmission, a growing compendium of observational evidence on the use of masks by the general public in several countries, individual values and preferences, as well as the difficulty of physical distancing in many contexts, WHO has updated its guidance to advise that to prevent COVID-19 transmission effectively in areas of community transmission, governments should encourage the general public to wear masks in specific situations and settings as part of a comprehensive approach to suppress SARS-CoV-2 transmission"

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Well, aside from the one study showing an increased risk of personal infection from a cotton mask, there is not much evidence to indicate that wearing a mask will actually hurt....so while they might not be much help, there's little downside to recommending them unless they make the general public less vigilant about other IPC.

 

I liked the conclusion of the NEJM authors best:

 

"Expanded masking protocols’ greatest contribution may be to reduce the transmission of anxiety, over and above whatever role they may play in reducing transmission of Covid-19."

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That is part of the rationale. It is cheap, feasible, and there is some low quality evidence, and this also means high quality research could show they are effective in the future. Also, we dont have a cure or vaccine for pandemic. So looking at the alternatives, risks, benefits,  cost, not unsurprising they went for a strong recommendation with low quality evidence

 

And does the forum only show new posts, if you are logged in? I noticed that when I logged in I saw a lot of new topics. 

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4 hours ago, anoopbal said:

And does the forum only show new posts, if you are logged in? I noticed that when I logged in I saw a lot of new topics. 

 

Well, if you have no stored cookie telling the board software when you were last here, it can't tell you what is "new" is, can it? So I don't think it will show you new posts unless logged in. 

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On 7/11/2020 at 11:53 AM, anoopbal said:

should encourage the general public to wear masks in specific situations and settings as part of a comprehensive approach to suppress SARS-CoV-2 transmission

 

I'm not sure I'd call that "strong" but it was definitely stronger than their first set of recommendations.

 

The specific situations part seems to be getting generally lost however....as the NEJM editorial I linked above notes, there is a time+distance function to viral transmission and brief interactions with infected people in public spaces are unlikely to result in infection...so wearing a mask on the sidewalk, at the gas station, to the drive-up window, etc. is really pointless....and don't even get me started about the people I see driving in their cars, alone, wearing a mask...

 

 

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7 hours ago, Something Anonymous said:

Mask wearing while driving a car baffles me as well. The only thing I can figure is that they are worried it will get sucked in through the AC....

 

I also watched an obviously married couple in their early 30s walking down the sidewalk together in a suburban neighborhood near here, nobody within literally a quarter mile of them, both wearing masks.

 

This is the sort of thing that results from public health officials doing a miserable job of explaining how masks work and how you become infected with the disease.

 

Sadly, that lack of good information to the public has been the hallmark of this pandemic in the US.

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13 hours ago, STENDEC said:

 

I'm not sure I'd call that "strong" but it was definitely stronger than their first set of recommendations.

 

 

 

True.I miswrote. I meant just a recommendation and  left it to individual countries to make their own recommendations. 

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