Face Masks Against COVID-19: An Evidence Review

Comment: If you read the actual study (and the revealing comments between researchers) you will find this is not at all comparable to the current situation and this study is far from saying anything definitive about the lack of effectiveness of masks. First, this is a study looking at people coughing from 20 cm away. Nobody is saying it is safe to let a sick person cough in your face at a close distance just because they are wearing a mask. Masks are in addition to social distancing, not in place of it. In short, the Seongman Bae study did not aim to verify whether surgical or cloth masks are able to shorten the trajectory of droplets emitted through coughing, speaking or breathing. Second, and more to your point, in the study itself, compared with the control condition, the petri dish viral load was less with a cloth mask for all patients, and in half, was not detectable at all. Such reductions do help at the population level. So, the data from the study actually support mask-wearing, coupled with other measures, as a precautionary strategy.

Comment: A virus cannot multiply outside the body like a bacteria can. The guidelines regarding face mask handling originate from the WHO and seem to be the general guidelines meant to also protect against spread of bacteria.

Unlike a bacteria, a virus is unable to multiply outside the host. The viral load on the outside of the mask is low compared to the viral load in saliva that is expelled from the mouth during speaking (especially susceptible are fricatives 'f', 's', 'v' and 'z' as well as sounds like 'p' and 't'). During a conversation at close distance and/or in noisy environments, some saliva may be transferred between persons as it is expelled from a speaking person and enters the mouth of a second person.

It seems reasonable to assume that fresh saliva being passed from an infected persons' mouth to a non-infected persons' mouth must have a much higher chance of spreading the virus than any mechanism by which viruses on the outside of a face mask can spread. It is difficult to imagine how a viable viral load would be able to transfer from the outside of a mask and cause a new infection. During every transfer from one surface to the next, the number of viruses on a surface decreases exponentially at minimum due to dilution alone. Additional decay of viruses that are damage during the transfer from one surface to the next increases the rate of decay even further.

Given the (speculated) low chances of the virus spreading through face mask or through surfaces in general, it seems awkward that the WHO is putting so much emphasis on face mask handling. Although this is appropriate for a hospital setting where health-care workers are potentially exposed to dangerous and resistant bacteria, this handling seems unnecessary and even counterproductive for face mask wearing, as it is used to argue against the wearing of face masks by the general public by some national health organizations.

Comment: The Seongman Bae et al. 2020 study has now been retracted: https://www.acpjournals.org/doi/10.7326/M20-1342

Comment: Face Mask Use and Control of Respiratory Virus Transmission in Households - MacIntyre, CR et al - Emerging Infectiuos Diseases - Feb-2009

The authors state that masks are effective, but in households the compliance was less than 50%. Doesn't help if you don't wear it.

The above article is freely downloadable.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2662657/

Comment: Facemasks have double effect:

With 100% mask efficacy, 35.5% usage reduces infections due to reduced emission by 35.5% and again by 35.5% due to reduced intake.

Hence formula to get from 2.4 to 1 is x= 1 - sqrt(1/2.4)

Comment: The WHO-published study cited by you (titled "Non-pharmaceutical public health measures for mitigating the risk and impact of epidemic and pandemic influenza") recommends face masks wearing by the public in case of a high severity pandemic (see page 3).

The studies that measure effectiveness of face mask wearing which are included in their meta-analysis are mainly in household settings. The study notes that "Some studies reported that low compliance in face mask use could reduce their effectiveness." (page 26). The low or unknown mask wearing compliance in these studies prevent any conclusion to be drawn. The study therefore concludes that "there was no evidence that face masks are effective in reducing transmission of laboratory-confirmed influenza."

The study recommends face mask wearing under circumstances currently present as the result of SARS-CoV-2 on the basis of mechanistic plausibility:

"Face masks worn by asymptomatic people are conditionally recommended in severe epidemics or pandemics, to reduce transmission in the community. Although there is no evidence that this is effective in reducing transmission, there is mechanistic plausibility for the potential effectiveness of this measure.

A disposable surgical mask is recommended to be worn at all times by symptomatic individuals when in contact with other individuals. Although there is no evidence that this is effective in reducing transmission, there is mechanistic plausibility for the potential effectiveness of this measure." (page 14).

The WHO-published study is therefore not a counterpoint to the conclusion of this studies, because:

• Mere absence of statistically significant evidence is not invalidating this studies;
• The WHO-published study recommends the wearing of face masks by the public during a high severity pandemic;
• The WHO-published study predates this studies and more empirical evidence whether face masks are effective has become available;
• The WHO-published study is about influenza which has differing characteristics compared to SARS-CoV-2.

Comment: Thank you for your comments.

The point I was making was that this article uses much of the studies that the study the WHO and CDC article, listed above in my original comment, would have also reviewed, and found them either to be overly bias (page 11 of WHO publication) or did not provide actual evidence during the Randomized Controlled Trials (RCT), that masks actually had the desired effect. Here they recognized the RCT's as the best actual evidence, as opposed to observational (which was lower than RCT but higher than computational model) or computer models - since these last two can be more prone to assumptions and bias that can lead to improper conclusions. These studies reviewed by the meta-study that underlies the WHO and CDC articles were from the dates 1946–July 27, 2018. While this pre-print article does include some newer publications, it appears it would be strengthened at minimum, if it also applied the same criteria to it's sources which are newer (addressing possible bias and evidence in the studies used), and to address the areas of older sources which would also be part of the underlying study in the WHO and CDC publications listed above, but were found to not actually support RCT evidence that masks had a significant impact on influenza.

I believe this is particularly important, since the point of this pre-print is explicitly geared toward influencing public policy. It also relies on studies that could easily be attributed to other, although probably less likely, conclusions. For instance, it talks about a case study of airline passengers coming from China. Yet, the underlying articles does not lead to the actual study. For instance, since the flight is coming from China, and some areas of China having been exposed to SARS-Cov-2 since Aug 2019, could it be that most of the passengers and crew were from that region and already had antibodies (had herd immunity been reached), or where was the COVID-19 passenger in their infectious stage, etc.. The second case study actually dealt with Influenza A, but made the statement "We recommend a more comprehensive intervention study to accurately estimate this effect." In regards to mask effectiveness as a recent meta-study, I can find similar articles, from authoritative publication sources, that point out opposite conclusions (that masks are somewhat effective in certain aspects, but have no clinical evidence that they actually have a significant impact on influenza), such as, as an example (although it is classified commentary, it does much of the meta-study review with citations):

https://www.cidrap.umn.edu/news-perspective/2020/04/commentary-masks-all-covid-19-not-based-sound-data .

This underscores the need to actually deal with any study bias or assumptions, and using a similar approach that the study that underlies the CDC and WHO publicans used, could help alleviate similar studies that have come to opposite conclusions (or at least not as strong of a conclusion as to the effectiveness of masks).

In addition, my other underlying point to this pre-print, since it explicitly is geared toward influencing public policy, is to ask the fundamental question: Is suppression of the virus actually the best course of action for those who are not fragile, or who are not protecting someone at home, or in a nursing home, who is fragile and has comorbidities? Up until now, the reason given for suppression and flattening the curve have relied upon a number of key assumptions, mainly that a vaccine was needed, and secondly that people would flawlessly perform until the vaccine was completed. Neither of these are reasonable in reality - humans are social and there will be contacts (particularly within households), and vaccines are also difficult to develop successfully for coronaviruses (not to mention anything of the actual approval process). There are other factors that should be considered - what about cross immunity as a form of immunization? What about natural herd immunity? What about the fact that COVID-19 as a virus is not really the detrimental part, it is the pneumonia that follows it (which with quick identification can be combated with antibiotics just as it would be with any influenza respiratory disease)? As Dr. Knut M. Wittkowski has pointed out in the links I provided above, suppression only keeps the respiratory disease in the population longer, widens the actual impact, and prevents it from being destroyed through natural herd immunity (or possibly by using a cross-immunity with SARS-Cov[-1]). While this is outside of the scope of the pre-print at first glance, since this pre-print is explicitly is geared toward influencing public policy, I believe it would be much stronger if it actually approached the potential assumption and bias topics of the underlying studies used and even delved into why it believes suppression, rather than quickly fostering natural herd immunity while attempting to protect the vulnerable, is the desired goal.

In regards to the bullet points:

• "Mere absence of statistically significant evidence is not invalidating this studies;"
  • This is true, but as I mentioned above, many of the studies this pre-print meta-analysis are dealing with, in regard to RCT's, would have been part of the underlying study of the CDC and WHO publications, that found either significant bias or inconclusive evidence for RCT's (with observational and computational being rated lower in actual evidence than RCT's). The newer studies mentioned in this article are not analyzed by the pre-print using the same type of evidence / bias analysis, which at minimum could make this study stronger (as well as address why the two studies come to fairly different conclusions - ie. how strong is the evidence that is underlying this meta-study pre-print).
• "The WHO-published study recommends the wearing of face masks by the public during a high severity pandemic;"
  • They did, but this, as you pointed out was based on mechanistic plausibility, not on actual evidence from RCT's. In other words, it does not hurt anything, and there is some reason to believe it might provide some suppression even though we do not have any RCT evidence that it actually does.
• "The WHO-published study predates this studies and more empirical evidence whether face masks are effective has become available;"
  • This is true, but again, much of the studies it included would have also been a part of the underlying study meta-analysis that the CDC and WHO publications were based upon. You mentioned household studies, but the CDC publication acknowledges that of the 10 RCT studies available in this time period, 7 were household studies - but even then, this pre-print article is recommending as a public policy that masks be used mainly by the full population, not just on the basis of it-might-help, but that there is significant evidence that it-does-help (if that is the case, and the majority of the people it would impact would be in the "home" category, it seems that the fact that 7 of the 10 studies were "home" studies actually strengthens the point that the evidence of available RCT's show that masks are not effective in real life scenarios). But, with the caveats I mentioned above, I concede it is a fair point.
• "The WHO-published study is about influenza which has differing characteristics compared to SARS-CoV-2."
  • Although the SARS's virus' are coronaviruses, they functions as an influenza respiratory disease would (as is pointed out by Dr. Wittkowski in the links I mentioned above), and for these purposes can be treated similarly. But, in regards to the mechanics of masks, the actual virus size of actual Coronavirus' are about 17nm to 90nm, whereas for Influenza it is about 80nm. These are way under the micrometers that masks will be able to block. As for the aerosol transmission aspect, of non-N95-or-above masks, they filter about .06 to .1 micrometers, and aerosols can be in the range of 10nm to 10 micrometers. So, in reality, for masks, the underlying study represented in the CDC and WHO publications that I linked to in my original comment would have the same mechanics for SARS related coronaviruses.
    • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4486061/
    • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7185834/