Resolved: public mask mandates assist in curbing the spread of Covid-19

I Took the Affirmative in a debate on this issue. This is my opening statement. The endnotes contain all the evidence that Rancourt mis-summarizes and misrepresents the studies he cites. It also explains the many errors that he makes in his argument, and the fallacies he commits.

Thanks Petar

While I do appreciate this opportunity, I’d like to begin by expressing my reservation about participating in this debate. Anyone curious about the effectiveness of mask mandates should listen to current medical and public health experts—epidemiologists and immunologists—not a debate between a philosopher/logician and a physicist who specialized in metals but no longer works or publishes in academia.

What’s more, there is really no debate to be had on this issue. There was a debate, in the scientific community, a few months ago—but it was settled very quickly once the evidence was laid out. Indeed, initially, I thought that public mask wearing was overkill. But then I learned how COVID spreads, and how prevalent asymptomatic spread of COVID is. To help curb its spread, all masks have to do is reduce the number of infected particles that exit an infected person’s mouth—and good evidence suggests they do. Since I am willing to update my beliefs in light of new evidence, I changed my mind.

This, Petar, is why you couldn’t find any medical experts for this debate; they’ve already had it. And engaging with pseudoscientific arguments risks legitimizing them. But I engage with pseudoscience for a living. And since this is one of those times that pseudoscience can kill, I decided to take this opportunity to (1) communicate the scientific argument on this issue to a broader audience and (2) debunk the pseudoscience. Fortunately, as a philosopher and logician, who teaches and publishes on logic, argumentation, philosophy of science, medical diagnosis, and medical pseudoscience—I am especially qualified to do these two things.  

Ok, so first: how and why masks assist in curbing the spread of Covid-19.

The explanation is simple, but misinformation has confused the issue. It’s commonly believed that masks simply protect their wearer from becoming infected by filtering the air that a person inhales. But while there is some evidence that cloth masks maybe offer some protection to their wearer in this regard,[1],[2] the primary way they help mitigate the spread is by filtering the air a person exhales—by [click] sneezing, coughing, speaking, or breathing.

Why are masks effective in filtering viruses from the exhaled air? Because a virus doesn’t travel by itself; it travels in droplets of moisture propelled from the mouth that can be captured. The largest droplets are intercepted by the surface of the mask; smaller ones are stopped by impaction as they try to make it through the mask; and the smallest, including aerosols, are diffused by the mask because of something called Brownian motion–the erratic way they move. This lowers the number of infected droplets in the air, and thus reduces the risk of exposure for other people.[3] [4]

Now, it’s important to note that, while all masks filter exhalations,[5] certain kinds of masks are better than others.[6] The early woven cloth masks were effective, but not as effective as later non-woven ones—what we today call “medical” or “surgical masks.” (According to Davies (et al, 2013), while both types are effective, surgical masks are about three times more effective. [7] [8] But different kinds of cloth, layered or combined, can offer better filtration, by making the pathway particles would have to travel to get through the mask more convoluted. Aydin (et al, 2020) found that layering cotton fabrics can make homemade masks almost as effective as surgical masks,[9] and Konda (et al, 2020) found that layering different kinds of fabrics (like cotton with flannel) could also increase their efficacy.  Such masks filtered 80% of particles smaller than 300 nanometers (0.3 microns) and 90% of those larger. [10] Filters can also improve mask efficacy.[11]

Now if an infected droplet is already in the air that a masked person is about to inhale, the mask will be less likely to catch that particle. That might make one question how cloth masks can filter the air that someone exhales. But that question is easily answered. Part of it is due to air flow; when you are breathing in, you are not pushing the air directly through the mask. But also–the longer a droplet is in the air, the more opportunity it has to evaporate and become smaller (and even aerosolize)—and (unless it’s smaller than 0.3 microns) the smaller it is, the less likely a particle is to be caught by a mask.[12] So infected droplets in the air that an unmasked person has exhaled has a better chance at making it through your mask. But most of the infected droplets exiting your mouth won’t, since they have not yet had a chance to evaporate.[13] [14]

In other words, masks unquestionably filter droplets (on the right), including most of them that would become aerosols (in the middle) And they can even capture those that start out small (on the far left), just less efficiently.

So, if you are in a room with a non-masked infected person, you are pretty likely to be infected even if you are wearing a cloth mask. However, if that infected person is wearing a cloth mask, you are much less likely to be infected—even if you are not wearing a mask. This is why it is said “My mask protects you, your mask protects me.”[15] Your choice to not wear a mask does not put you at risk; it puts others at risk.

Now, since the fact that the majority of the work that masks do in curbing the spread of COVID is done by the masks that infected persons are wearing, one might wonder …

… why we don’t just have infected people wear them. Indeed, this was part of the reasoning behind the traditional ], years long, CDC and WHO recommendations that said mask wearing is not necessary for seemingly healthy individuals. With many diseases it is not. But then experts realized just how long a person could be infected with COVID without knowing it, and even that many infected never have any symptoms.[16] Consequently, public mask mandates are the only way to ensure that infected persons—including those who are pre- or asymptomatic—are wearing a mask. Such mandates would thus reduce the number of infected people without masks, thus reduce the number of infected particles in the air, and thus reduce the probability of transmission. Once we realized this, mask wearing was recommended. Granted, the CDC and WHO lagged behind the experts in this regard. But scientists change their mind based on evidence all the time. That’s not unusual. It’s just usually not that public.

So given what we know masks do, the fact that mandating them helps curb the spread of COVID is just common sense. But the evidence also bears this out. Now you can’t do a direct, controlled experiment where you blindly throw non-infected people into rooms with masked or un-masked infected persons, and see if they get sick. That’s unethical. But all the ethical ways to study this question indirectly indicate that cloth masks curb the spread.

For example, transmission rates slowed in hospitals (Sung (2016)[17] Wang, et. al., 2020),[18] German cities (Mitz, et. al 2020),[19] North Texas (Nandy, 2020),[20] and in US states (Lyu & Wehby, 2020),[21] after mandates went into effect. (In Germany, they reduced growth rates by 40%.) What’s more, U.S. States with mandates have seen much less spread than those without, [22] as have countries where mask use is popular.[23] Modeling has also confirmed the effectiveness of mask mandates.[24] According to Stutt (et. al., 2020)[25] and Eikenberry (et. al., 2020), if masks are just 50% effective, they could help bring down infection rates to non-epidemic levels and reduce the death rate by as much as 45%. Large reviews of observational and comparative studies have also concluded that mask mandates are highly effective,[26] as have collections of collaborating experts.[27] And, of course, there were those infected hairstylists in Missouri who didn’t pass it on to 140 of their clients because they were wearing a mask.[28]

The IHME found that mask mandates could save 33,000 by October 1st,[29] and (according to Brooks, 2020) if everyone worse a mask, we could get the pandemic under control in four to eight weeks.[30] None of this is as good evidence as the above described unethical blinded study would provide, but it is literally as good as one could reasonably expect.[31] Indeed, because we are not dealing with a drug, this evidence makes randomized controlled trials unnecessary.

Now, Rancourt self-published an article he titled “Masks Don’t Work” where he suggests that the science indicates otherwise—but that brings me to the second part of my opening argument: debunking the pseudoscience.

In his article “Masks Don’t Work,” Rancourt offers a survey of seven (7) studies which he says prove that “masks don’t work.” But…

First, it’s not a true survey of the literature. Rancourt just combed through studies to find the ones he thinks support his position, and ignored the rest.  In logic, we call this “confirmation bias.” At best, it only proves some people can find some evidence for anything.”

Second, the majority of the studies he cites, like Smith (et. al. 2016) are irrelevant to his claim. They are about whether N95 masks protect their wearer better than surgical masks, not about whether cloth masks filter exhaled air. So he’s equivocating on the word “mask” and what it means for a mask “to work.” What’s more, although it is very unlikely that a surgical mask offers just as much protection as (properly sealed) N95 masks[32]even if they did, that wouldn’t even prove that cloth masks can’t filter inhaled air, much less exhaled air. With all protective equipment, you are bound to reach an upper limit, where adding more protection is just overkill.

Third, the other studies he mentions simply don’t say what he claims they do. For example, his quote from bin-Reza (2012) read “None of the studies established a conclusive relationship between mask/respirator use and protection against influenza infection.” This implies that the study concluded that there is no benefit to wearing masks or respirators. In reality, however, the slash in the “mask/respirator” phrase is meant to indicate a comparison between the two—the study is actually saying that they are equally effective, not lumping them together and declaring them both ineffective. Several of the sentences before and after the one he quote mines demonstrate this. 

“Eight of nine retrospective observational studies found that mask and ⁄ or respirator use was independently associated with a reduced risk of severe acute respiratory syndrome (SARS).”

And SARS, by the way, is the most analogous disease to COVID-19.

The text accompanying the other studies contain similarly misleading quotes or summaries.  As Jacobs (2009) said to me in correspondence,

Dr. Rancourt’s opinion piece mischaracterizes the research findings I reported in my 2009 peer-reviewed article…. It was not designed to examine mask effectiveness of preventing the mask-wearer from spreading a respiratory infection. My study has no bearing on addressing that recommendation…. [and] The mask used was a typical surgical (disposable paper) mask, not an N-95 respirator mask as [Rancourt] states in his article.

And the conclusions of others just outright contradict his thesis.

“There is some evidence to support the wearing of masks or respirators during illness to protect others, and public health emphasis on mask wearing during illness may help to reduce influenza virus transmission.” Cowling (et. al., 2010)

In other words, Rancourt scoured the literature, and the best he could do is find studies that don’t actually support his thesis, but which he could misquote or mis-summarize to make it look like they do.[33]

The second argument he presents cites Shaman’s 2010 article which suggests that humidity is responsible for seasonal variation in flu infections. From this he somehow concludes that masks cannot mitigate the spread. But (1) Shaman himself has said that we don’t know enough about COVID to conclude that humidity is a factor in its transmission[34]—and the fact that COVID is spreading like wildfire in Florida and Texas in July seems to indicate that it is not. Indeed, experts agree, that with new diseases, it’s not. [35] (2) This argument relies on the assumptions that COVID spreads solely via aerosols and masks don’t prevent aerosols from existing in the air; both of these assumptions are false. And (3) humidity causing seasonal variation wouldn’t mean that masks don’t work because humidity is not the only causal factor in transmission. There also is contact and contamination; thus, measures restricting those, like masks, would mitigate spread. In my logic class, we would call Rancourt’s error here “the fallacy of oversimplified cause.”[36]

Rancourt’s third argument suggests that infected droplets are too small to be blocked by N95 respirators, much less cloth masks. But here, he is not only (1) talking about inhalation not exhalation, (2) making false assumptions about aerosols and transmissibility, and (3) fallaciously appealing to incredulity to favor dubious theories, but (4) he doesn’t understand how N95 masks work; contrary to what he claims, because of Brownian motion, N95 filters are actually more efficient at filtering particles smaller than 0.3 microns. They are not sieves. Neither are most cloth masks.[37]

Lastly, Rancourt argues that, because masks can’t guarantee 0% exposure, they are useless. But here, he not only, again, (1) misrepresents the evidence[38] (2) makes unsupported assumptions about the minimal infective dose of COVID and a mathematical error that exaggerates the infectious potency of aerosols 10-million-fold,[39] and (3) fails to recognize that symptom severity could be proportional to the amount of viral exposure[40]—but (4) his argument is a prime example of the “all or nothing fallacy.” Yes, masks would need to 100% effective to completely stop the spread of COVID—but not to slow it. By merely reducing the amount of infected droplets in public places, they reduce spread.[41] Seatbelt laws are not 100% effective; some people still speed and accidents still happen. That doesn’t mean speed limits don’t reduce accidents.

Now, I do not expect any of this to have any effect on Rancourt or those in his echo chamber. They think otherwise for ideological reasons, not evidence based scientific ones. And you cannot reason someone out of a position that they did not reason themselves into. But what I have presented here is enough to convince any fair, open-minded person that, yes, indeed, public mask mandates assist in curbing the spread of Covid-19. Indeed, for them to do so, masks only need to do what we already knew they do: catch droplets. If they were unable to do this, the successful use of HEPA filters (which operate on the same principles as mask) in nearly every segment of the economy, and in your vacuum cleaner, would just be a giant coincidence. The burden of proof is thus on Rancourt to show otherwise. Needless to say, misrepresenting the scientific evidence and offering fallacious arguments does not meet that burden. 


[1] The cloth masks do somewhat filter the air we breathe in, but not enough to be effective in high risk environments. According to this article, some researchers are starting to suspect that they offer some protection to wearers in low-risk public environments, and studies to test this are hopefully coming soon. Caitlin McCabe, “Face Masks Really Do Matter. The Scientific Evidence Is Growing,” The Wall Street Journal, July 18, 2020, https://www.wsj.com/articles/face-masks-really-do-matter-the-scientific-evidence-is-growing-11595083298  On whether medical/surgical (non-woven) masks are effective at protecting their wearer in high risk environment, the evidence seems to be mixed. MacIntyre (et al., 2014) showed that, while medical (surgical) masks provided some protection to the wearer in such environments, cloth masks provided almost none. See C. Raina MacIntyre, et al. “A Cluster Randomised Trial of Cloth Masks Compared with Medical Masks in Healthcare 1Workers,” BMJ Open 5 no. 4, (2015) https://doi.org/10.1136/bmjopen-2014-006577. The results in Seto (2003) and (Nishiura , 2005) also suggested that surgical masks do work to protect health care workers.  WH Seto,et al., “Effectiveness of Precautions Against Droplets and Contact in Prevention of Nosocomial Transmission of Severe Acute Respiratory Syndrome (SARS),” The Lancet 361, no 9368 (May 3, 2003): 1519-20, https://doi.org/10.1016/S0140-6736(03)13168-6. and Hiroshi Nishiura, et al., “Rapid Awareness and Transmission of Severe Acute Respiratory Syndrome in Hanoi French Hospital, Vietnam,” Am J Trop Med Hyg 73, no. 1 (July 2005): 17-25, https://pubmed.ncbi.nlm.nih.gov/16014825/. And Zhang (2009) suggests that they can protect even the general public. Lijie Zhang, et al., “Protection by Face Masks against Influenza A(H1N1)pdm09 Virus on Trans-Pacific Passenger Aircraft, 2009,” Emerging Infectious Diseaes 19, no. 9 (September 2013): 1403-10, https://doi.org/10.3201/eid1909.121765. But then Kähler (et al., 2020) seems to suggest that surgical (or similar) masks probably don’t provide sufficient protection for the wearer against droplet infection; only property fitted particle-filtering (e.g., N95) masks can do that. But all such studies are plagued by things like recall bias.
                When it comes to protecting others by filtering the air that a person breathes out, the study found that a simple mouth and nose cover is enough. Such masks are effective at limiting droplet emission when coughing, sneezing, speaking, singing, or breathing. Face coverings significantly reduce the spread of viruses and thus public mask wearing is “a very useful contribution to contain a pandemic.”  See Christian J. Kähler and Rainer Hain, “Fundamental Protective Mechanisms of Face Masks Against Droplet Infections,” Journal of Aerosol Science 148 (2020) https://doi.org/10.1016/j.jaerosci.2020.105617.

                [2] See also Rick Kushman, “Your Mask Cuts Own Risk by 65 Percent,” UC Davis, July 6, 2020, https://www.ucdavis.edu/coronavirus/news/your-mask-cuts-own-risk-65-percent/

[3] Talib Dbouk and Dimitris Drikakis, “On Respiratory Droplets and Face Masks,” Physics of Fluids 32, no. 063303, published electronically June 16, 2020, https://doi.org/10.1063/5.0015044.

[4] Bhanu Bhakta Neupane, Sangita Mainali, Amita Sharma, and Basant Giri, “Optical Microscopic Study of Surface Morphology and Filtering Efficiency of Face Masks,” PeerJ 7,no. e7142 (2019), https://doi.org/10.7717/peerj.7142.

[5] Two more studies on mask effectiveness:
Qing-Xia Ma, et al, “Potential Utilities of Mask-Wearing and Instant Hand Hygiene for Fighting SARS-CoV-2” Journal of Medical Virology (2020) https://doi.org/10.1002/jmv.25805.

This study suggested that 95% of viruses in aerosols could be blocked by homemade masks, and 97% could be blocked by surgical masks.

Nancy H. L. Leung, et al., “Respiratory Virus Shedding in Exhaled Breath and Efficacy of Face Masks,” Nature Medicine 26 (2020): 676-80, https://doi.org/10.1038/s41591-020-0843-2.
This is a study out of Hong Kong which suggested that people wearing a mask was very effective at reducing transmission of alpha coronaviruses.

[6] Cloth masks of only one material seem to have very little effectiveness: Samy Rengasamy, Benjamin Eimer, and Ronald E. Shaffer, “Simple Respiratory Protection – Evaluation of the Filtration Performance of Cloth Masks and Common Fabric Materials Against 20-1000 nm Size Particles,” Annals of Occupational Hygiene 54, no. 7 (October 2010): 789-98, https://doi.org/10.1093/annhyg/meq044. This is why those who are just wearing bandanas, or pulling their t-shirt over their mouth, are not doing anyone any good.

[7]  Both types “significantly reduced the number of microorganisms expelled by volunteers,” the “the surgical mask was 3 times more effective.”) Anna Davies, et al., “Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?” Disaster Medicine and Public Health Preparedness 7, no. 4 (August 2013): 413-8, https://doi.org/10.1017/dmp.2013.43.

                [8] Milton (2013) found that surgical masks decreased emission of large particles by 25 fold, and aerosols by 3 fold in flu patients. See Donald K Milton, et al., Influenza Virus Aerosols in Human Exhaled Breath: Particle Size, Culturability, and Effect of Surgical Masks,” PLoS Pathogens 9, no. 3 (March 2013): 1-7, https://doi.org/10.1371/journal.ppat.1003205. 5

[9] Aydin et al, 2020, suggests that layering great increases the filtering efficiency of cloth masks while also maintaining some breathability, Onur Aydin, et al., “Performance of Fabrics for Home-Made Masks Against the Spread of Respiratory Infections through Droplets: A Quantitative Mechanistic Study,” medRxiv,preprint, submitted July 8, 2020  https://doi.org/10.1101/2020.04.19.20071779.

[10] “Overall, we find that combinations of various commonly available fabrics used in cloth masks can potentially provide significant protection against the transmission of aerosol particles.” Abhiteja Konda, Abhinav Prakash, Gregory A. Moss, Michael Schmoldt, Gregory D. Grant, and Supratik Guha, “Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks,” ACS Nano 14, no. 5 (2020): 6339-47, https://doi.org/10.1021/acsnano.0c03252.

[11] Dr. Marty, a professor of infectious diseases at Florida International University told “Good Morning America.” “But if you add that filter, then you’re also adding a really good protection for yourself.” See Becky Worley, Anthon Kane, Robyn Weil, and Angeline Jane Bernabe, “Face Masks With Filter add Another Layer of Protection, Experts Say,” GMA, July 16, 2020, https://abcnews.go.com/GMA/Wellness/face-masks-filters-add-layer-protection-experts/story?id=71811792.

[12] That’s not quite accurate. Particles around .3 microns are actually the hardest to catch. Those smaller are easier to catch because of Brownian motion. But this actually helps my thesis, so for simplicity I shall leave this nuanced point to the side.

[13] This is actually what N95 masks are for; they protect their wearer by being 95% effective at filtering the air that a person breathes in. And because they often have unfiltered exhaust vents, they usually don’t filter the air a person breathes out. Combine that with the fact that they don’t even perform their intended function well unless they are perfectly fit, and you can realize why they should likely only be worn by health care workers in high risk environments. It’s my estimation that the use of N95 masks by the general public likely wouldn’t help curb the spread of COVID-19 as well as the use of cloth masks.  But I’m happy to be corrected on that point.

[14] Some clarification here is useful. Technically, depending on how you classify “aerosoles” (definitions range from 5 microns to 100 microns), most of  the particles you breath out could be classified as arisoles–and depending on their size, the mask will filter them with different efficiencies. Even cloth masks are very good at filtering down to 10 microns, pretty good down to 5 microns, but not great below 5. Neupane, “Optical Microscopic Study of Surface Morphology and Filtering Efficiency of Face Masks.”

In one way, this is concerning because (according to Burch (2020), the average size for aerosoles leaving your mouth is 3 microns.  The good news is, despite the fact that they make up the largest number, they only represent 0.00024% of the liquid leaving your mouth during a cough. Consequently, very few of them are infected (at worst 1 out of every 700). A full “ 99.99976% of the viruses sprayed during a cough are carried in droplets — not aerosols.’) So the majority of transmission happens from droplets.  What’s more, the deadliest aerosoles are those that started out as droplets, but then evaporated down; they have higher concentrations of the virtus. Masks catch those.  Sso the inability of masks to filter out 3 micron arisles does not greatly hinder their ability to keep infected particles out of the air, and thus does not prevent them from efficiently preventing the spread of covid.
                Adrien Burch, “A Microscopic Perspective on Airborne COVID-19,” The Medium, March 31, 2020, https://medium.com/better-humans/should-you-be-worried-about-catching-covid-19-from-aerosols-6c97d023bb6d.

[15] From the abstract of: Richard O. J. H. Stutt, Renata Retkute, Michael Bradley, Christopher A. Gilligan, and John Colvin, “A Modelling Framework to Assess the Likely Effectiveness of Facemasks in Combination with ‘Lock-down’ in Managing the COVID-19 Pandemic,” Proceedings of the Royal Society A (2020) https://doi.org/10.1098/rspa.2020.0376.

[16] Wycliffe E Wei, Zongbin Li, Calvin J Chiew, Sarah E Yong, Matthias P Toh, and Vernon J Lee, ”Presymptomatic Transmission of SARS-CoV-2-Singapore, January 23-March 16, 2020,” MMWR Morb Mortal Wkly Rep. 69, no. 14 (April 2020): 411-5, https://doi.org/10.15585/mmwr.mm6914e1.

                [17]Anthony D Sung, et al. “Universal Mask Usage for Reduction of Respiratory Viral Infections after Stem Cell Transplant: a Prospective Trial,”  Clin Infect Dis 63, no. 8 (October 2016): 999-1006, https://doi.org/10.1093/cid/ciw451.

[18] Xiaowen Wang, Enrico G. Ferro, Guohai Zhou, et al., “Association Between universal Masking in a Health Care System and SARS-CoV-2 Positivity Among Health Care Workers,” JAMA,published electronically July 14, 2020, https://doi.org/ 10.1001/jama.2020.12897. In this study, cases of COVID-19 declined after mask mandates were put into effect in hospitals (that required all health care workers and patients to mask up). The study concluded that such mandates  reduce the transmission of SARS-CoV-2.

[19] Timo Mitze, Reinhold Kosfeld, Johannes Rode, and Klaus Wälde, “Face Masks Considerably Reduce COVID-19 Cases in Germany: A Synthetic Control Method Approach,” IZA (June 2020) http://ftp.iza.org/dp13319.pdf.

This study shows the impact of mask mandates in Germany. In Jena, for example, the first German city to enact such a mandate, COVID-19 cases fell by almost 25% in 20 days. The study concluded that similar mandidats could ruse the daily growth rate by 40% in the long term, although it did acknowledge that, outside Germany, different norms and climatic conditions in other countries might result in different protective outcomes.

                [20] “HSC COVID-19 Report #5 – July 20, 2020,” University of North Texas Health Science Center at Fort Worth, https://www.scribd.com/presentation/469858261/COVID-19-Report-July-20-Updated?fbclid=IwAR1ta8C-x5yYfpqQ5eghmiPFr42ndbA6rYCmTv3WbcGU9tDt3a_RU1BOIL0.

[21] In those 15 US States, they likely prevented up to 450,000 cases in under two months. Wei Lyu and George L. Wehby, “Community Use of Face Masks and COVID-19: Evidence from a Natural Experiment of State Mandates in the US,” Health Affair 39, no. 8 (2020): 1-7, https://doi.org/ 10.1377/hlthaff.2020.00818.

This was a retrospective analysis which examined the effects that different governmental orders to wear face masks had on COVID-19 growth rates, from April 9-May 15, 2020. It estimated that they prevated between 230,000 and 450,000 cases by May 22 (a reduction of 14-27%).

[22] Kasra Zarei and John Duchneskie, “Coronavirus Cases Rise in States with Relaxed Face Mask Policies,” The Philadelphia Inquirer, June 24, 2020, https://www.inquirer.com/health/coronavirus/covid-19-coronavirus-face-masks-infection-rates-20200624.html.

                [23] American Thoracic Society, “Countries with Early Adoption of Face Masks Showed Modest COVID-19 Infection Rates,” Medical Xpress, June 24, 2020, https://medicalxpress.com/news/2020-06-countries-early-masks-modest-covid-.html.

                [24] Samantha M. Tracht, Sara Y. Del Valle, and James M. Hyman, “Mathematical Modeling of the Effectiveness of Facemasks in Reducing the Spread of Novel Influenza A (H1N1),” Plos One 5, no. 2 (February 2010): 1-12, doi.org/10.1371/journal.pone.0009018.

[25] Stutt, et al.,“A Modelling Framework to Assess the Likely Effectiveness of Facemasks in Combination with ‘Lock-down’ in Managing the COVID-19 Pandemic.”

To keep the infection rate (R0) below 1.0, the authors argue for widespread use of face masks. “[F]acemask adoption by entire populations would have a significant impact on reducing COVID-19 spread.” “[I]n summary, our modelling analyses provide support for the immediate, universal adoption of facemasks by the public.”

[26] Derek K Chu, et al., “Physical Distancing, Face Masks, and Eye Protection to Prevent Person-to-person Transmission of SARS-CoV-2 and COVID-19: A Systematic Review and Meta-analysis,” The Lancet 395, no. 10242 (2020): 1973-87, https://doi.org/10.1016/S0140-6736(20)31142-9.

This was a review of 172 observational studies and 44 relevant comparative studies. The authors concluded “Face mask use could result in a large reduction in risk of infection.”

[27] Kimberly A. Prather, Chia C. Wang, and Robert T. Schooley, “Reducing Transmission of SARS-CoV-2,” Science 368, no. 6498 (June 2020): 1422-24, https://doi.org/10.1126/science.abc6197. In this paper, aerosol chemists and an infectious disease specialist argue that, because “airborne spread from undiagnosed infections will continuously undermine the effectiveness of even the most vigorous testing, tracing and social distancing programs,” the widespread use of masks are necessary to help prevent the spread of COVID. Both analytical information about the virus and information about countries where masks are commonplace was used.

Catherine M. Clase, et al., “Cloth Masks May Prevent Transmission of COVID-19: An Evidence-Based, Risk-Based Approach,” Annals of Internal Medicine, published electronically May 22, 2020, https://doi.org/10.7326/M20-2567. This study, done by an international research team of medical doctors and other medical specialists not only concluded that cloth masks worn by the public will reduce COVID-19 transmission rates, but that the benefits of widespread mask use outweigh any risks that may be brought about by wearing masks (such as improper use).

                [28] M. Joshua Hendrix, Charlse Walde, Kendra Findley, and Robin Trotman, “Absence of Apparent Transmission of SARS-CoV-2 from Two Stylists After Exposure at a Hair Salon with a Universal Face Covering Policy – Springfield, Missouri, May 2020,” Weekly 69, no. 28 (July 1, 2020): 930-32, http://dx.doi.org/10.15585/mmwr.mm6928e2external icon.

[29] “New IHME COVID-19 Model Projects Nearly 180,000 US Deaths,” IHME,June 24, 2020, http://www.healthdata.org/news-release/new-ihme-covid-19-model-projects-nearly-180000-us-deaths.

[30] For the quote, see McCabe, “Face Masks Really Do Matter.” For the evidence behind it, see  John T. Brooks, Jay C. Butler, Robert R. Redfield, “Universal Masking to Prevent SARS-CoV-2 Transmission – The Time is Now,” Jama, published online July 14, 2020, https://doi.org/10.1001/jama.2020.13107.

[31] for more such evidence, see “Face Masks – A Summary of Relevant Research Papers for COVID-19,” Sound Reason & More,June 11, 2020, https://soundreasonandmore.wordpress.com/2020/06/11/face-masks-a-summary-of-relevant-research-papers-for-covid-19/.

[32] See Sergey A. Grinshpun, et al., “Performance of an N95 Filtering Facepiece Particulate Respirator and a Surgical Mask During Human Breathing: Two Pathways for Particle Penetration,” Journal of Occupational and Environmental Hygiene 6, no. 10 (2009): 593-603, https://doi.org/10.1080/15459620903120086. See also C Raina MacIntyre, et al., “The Efficacy of Medical Masks and Respirators Against Respiratory Infection in Healthcare Workers,” Influenza and Other Respir Viruses 11, no. 6 (November 2017): 511-17, https://doi.org/10.1111/irv.12474. See also Loeb M, McGeer A, Henry B, et al. “SARS among critical care nurses,” Toronto. Emerg Infect Dis 2004 Feb;10(2):251-5.

[33] Here is a full rundown of how Rancourt misrepresents the studies he cites, and how they are either irrelevant to his thesis, or actually contradict it.

Joshua L. Jacobs, et al., “Use of Surgical Face Masks to Reduce the Incidence of the Common Cold Among health Care Workers in Japan: A Randomized Controlled Trial,” Am J Infect Control 37, no. 5 (June 2009): 417-19, https://doi.org/ 10.1016/j.ajic.2008.11.002.

This study showed that N95 masks cause headaches in some, and that (surgical) facemasks don’t protect their wearer. This only tells us what we already know: Wearing a tight banded mask on your face for 12 hours is bound to cause headache, and surgical masks don’t provide adequate protection in high risk environments. And since both findings are irrelevant to whether cloth masks filter outgoing particles, this study is irrelevant to his thesis.

B.J. Cowling, Y. Zhou, D.K.M.Ip, G.M.Leung, and A.E. Aiello, “Face Masks to Prevent Transmission of Influenza Virus: A Systematic Review,” Epidemiology & Infection 138, no. 4 (January 2010): 449-456, https://doi.org/10.1017/S0950268809991658.

The part of the study that Rancourt mentions is about whether masks (in this case, cloth masks) protect their wearer from infection, not whether they filter exhaled air and thus protect others. So it is irrelevant to his thesis. What’s more, the authors admit that the body of evidence they are examining is not sufficient to draw a conclusion, but also suggest that the evidence that does exist at least suggests that cloth masks do provide some protection for their wearer—probably not enough for a healthcare setting, but maybe enough for household use. They recommend further study on this topic. The part of the study that Rancourt doesn’t mention is the part that examines whether cloth provides protection to others by filtering air, and they conclude that they do. Rancourt is engaged in major confirmation bias here, by just leaving that part out.

Faisal bin-Reza, Vicente Lopez Chavarrias, Angus Nicoll, Mary E. Chamberland, “The use of masks and respirators to prevent transmission of influenza: a systematic review of the scientific evidence,” Influenza and Other Respiratory Viruses 6, no. 4 (December 2011): 257, https://do8i.org/ 0.1111/j.1750-2659.2011.00307.x.

As I mentioned in my opening statement, Rancourt uses a misleading quote from this one to imply that it found that “mask/respirators” don’t work, when in fact it found that they work equally well. What’s more, the part of the study Rancourt cities is about influenza, not COVID—and the authors themselves specifically state that their findings about influenza cannot be extrapolated to SARS-CoV-1 (“SARS is an unusual acute viral respiratory infection with a very different epidemiology to almost all other respiratory viral infections. It is fundamentally different from human influenza.”) But SARS-CoV-1 is very similar to SARS-CoV-2 (the cause of COVID-19), and about SARS-CoV-1 this study “found that mask and ⁄or respirator use was independently associated with a reduced risk of severe acute respiratory syndrome.”

Jeffrey D. Smith, et al., “Effectiveness of N95 Respirators Versus Surgical Masks in Protecting Health Care Workers from Acute Respiratory Infection: a Systematic Review and Meta-analysis,” CMAJ 188, no. 8 (May 2016): 567-74, https://doi.org/10.1503/cmaj.150835.

This study compares the effectiveness of N95 and surgical masks; as I explain in the main text of my opening statement, this makes it irrelevant to his thesis. What more, it admits that it doesn’t prove that they do offer equal protection; just that the available evidence so far is inadequate for proving that N95 masks offer more protection in a clinical setting. “Although N95 respirators appeared to have a protective advantage over surgical masks in laboratory settings, our meta-analysis showed that there were insufficient data to determine definitively whether N95 respirators are superior to surgical masks in protecting health care workers against transmissible acute respiratory infections in clinical settings.” However, even though it was not enough to prove they were superior, they did find that “In general, compared with surgical masks, N95 respirators showed less filter penetration, less face-seal leakage and less total inward leakage under the laboratory experimental conditions described.” So this is far from proof that N95’s don’t work better than masks.

Vittoria Offedu, et al., “Effectiveness of Masks and Respirators Against Respiratory Infections in Healthcare Workers: A Systematic Review and Meta-Analysis,” Clinical Infectious Diseases 65 no. 11, (December 2017): 1934–42, https://doi.org/10.1093/cid/cix681.

Again, this study is about whether N95 and surgical masks protect their wearer—specifically healthcare workers in high risk settings. It is not about whether cloth masks protect others by catching expelled droplets of COVID. So it is irrelevant to the issue. (It found that N95 masks do protect better than surgical masks against clinical respiratory illness, but that N95 and surgical masks protect against viral infections and influenza-like illness equally well. Rancourt takes the quote about this (“Evidence of a protective effect of masks or respirators against verified respiratory infection (VRI) was not statistically significant” out of context to make it seem like it is about the effectiveness of masks.) What’s more, it specifically found that masks and respirators do protect against SARS (which, again, is the closest thing to Covid-19). Indeed, it specifically stated that “This systematic review and meta-analysis supports the use of respiratory protection.”

Lewis J. Radonovich, Michael S. Simberkoff, and Mary T. Bessessen, “N95 Respirators vs Medical Masks for Preventing Influenza Among Health Care Personnel: A Randomized Clinical Trial,” JAMA 322, no. 9 (2019): 824–833, https://doi.org/10.1001/jama.2019.11645.

Again, this study compares the effectiveness of N95 and medical masks; as I explain in the main text of my opening statement, this makes it irrelevant to his thesis. What’s more, it’s about the flu—not SARS, so its findings really can’t be transferred over to COVID. Also, the non-difference could just be due to the N95’s not being properly sealed or used.

Youlin Long, et al., “Effectiveness of N95 respirators versus surgical masks against influenza: A systematic review and meta-analysis,” J Evid Based Med 13 (2020): 93-101, https://doi.org/0.1111/jebm.12381.

Again, this study compares the effectiveness of N95 and medical masks; as I explain in the main text of my opening statement, this makes it irrelevant to his thesis. And again, it’s about the flu—not SARS, so its findings really can’t be transferred over to COVID. It merely suggests that N95 masks should be reserved for health care workers in the most high risk situations—not that cloth masks can’t filter out droplets.

For this rundown, I partially relied on information provided here:  “Confirmation Bias Masks Truth OR Confirmation Bias, Masks, Truth,” Sound Reason & More,June 30, 2020, https://soundreasonandmore.wordpress.com/2020/06/30/confirmation-bias-masks-truth-or-confirmation-bias-masks-truth/?fbclid=IwAR38Vw0Ev6l5CU8bdn3f5uLsgPSkJErKyj07WPZiad-q0IcHxTl8mdH10o8.
                In other notes, I also relied on some information provided here: “Face Masks – A Summary of Relevant Research Papers for COVID-19.”

[34] Alan Yu, “What Happens to the Coronavirus When It Gets Warmer?” Whyy, May 20, 2020, http://whyy.org/articles/what-happens-to-the-coronavirus-when-it-gets-warmer 

                [35] Quote from: Alan Yu, “What Happens to the Coronavirus When It Gets Warmer?” Whyy, May 20, 2020, https://whyy.org/articles/what-happens-to-the-coronavirus-when-it-gets-warmer/. Here is the study: Rachel E. Baker, Wenchang Yang, Gabriel A. Vecchi, C. Jessica E. Metcalf, and Bryan T. Grenfell, “Susceptible Supply Limits the Role of Climate in the Early SARS-CoV-2 Pandemic,” Science 369, no. 6501 (July 17, 2020): 315-19, https://doi.org/10.1126/science.abc2535.   

[36] To illustrate this fallacy, imagine that we forcibly locked everyone in a separate room for two months to mitigate the spread of the flu. This would be a bad idea for multiple reasons, but that level of isolation would obviously mitigate the spread. No physical contact means no spread. But now imagine someone said, “It won’t mitigate the spread at all because humidity explains seasonal variation.” Wouldn’t we laugh them out of the room. Even if humidity is normally a major factor, that doesn’t mean physical contact is not also a factor—and so it doesn’t mean that keeping people from being in contact wouldn’t mitigate the spread. Of course it would. In the same way, so would reducing the number of infected droplets in the air with masks.

[37] Just below 0.3 microns is where Brownian Motion starts, so 0.3 micron particles are actually the hardest to capture. N95 masks are so named because they are 95% efficient at capturing such particles. They are actually more efficient at capturing particles both larger and small than that.  “N95s – Sufficient Protection for Covid19?” https://www.sphosp.org/wp-content/uploads/2020/04/Letter-in-response-to-N-95-use-RA-Final.pdf. See also Olof Gustafsson, Simon Gustafsson, Levon Manukyan, and Albert Mihranyan, “Significance of Brownian Motion for Nanoparticle and Virus Capture in Nanocellulose-Based Filter Paper,” Membranes 8, no. 4, published online October 5, 2018, https://doi/org/10.3390/membranes8040090.  

                [38] Prasith Baccam, Catherine Beauchein, Catherine A Macken, Frederick G Hayden, and Alan S Perelson, “Kinetics of Influenza A Virus Infection in Humans,” Journal of Virology 80, no. 15 (August 2006): 7590-9, https://doi.org/ 10.1128/JVI.01623-05 and Christopher B Brooke, William L Ince, Jens Wrammert, Rafi Ahmed, Patrick C Wilson, Jack R Bennink, and Jonathan W Yewdell, “Most Influenza A Virions Fail To Express at Least One Essential Viral Protein,” Journal of Virology87, no. 6 (March 2013): 3155-62, https://doi.org/ 10.1128/JVI.02284-12 They only talk about how quickly or efficiently viruses reproduce in cells once they are infected–not the probability of cells becoming infected once exposed.

[39] What’s more, he makes a mathematical error that greatly overestimates how many viruses would be in an aerosolized droplet. He says that “there are 1000 to 10 million viral particles, in each microdroplet 1 to 10 microns in size.” But, in fact, microdroplets of that size are mostly empty of virus and contain at most a single viral particle. Why? Because it’s difficult to get coronavirus into a concentration much higher than 10 million per mL (plaque forming units per milliliter)[39]; and a 10 micron droplet is (4/3 * 5^3 * 10^-18 m^3 =) 0.167 picoliter. A ml is 1 billion picoliters. So for every 1,000 10 micron droplets, only at most 2 (1.67) will have even a single virus in it—that’s roughly 1 out of every 600. So he is making an mathematical error of a factor of at least 10 million here. (My thanks to MW and my wife for the math!) And since it is far from established that one virus is sufficient for an infection, much less a severe on, his argument here is based on nothing. Source: Yinon M Bar-On, Avi Flamholz, Rob Phillps, and Ron Milo, “SARS-CoV-2 (COVID-19) By the Numbers,” eLIfe 9, no. e57309, published online April 2, 2020, https://doi.org/10.7554/eLife.57309.  

                [40] Carl Heneghan, Jon Brassey, and Tom Jefferson, “SARS-CoV-2 Viral Load and the Severity of COVID-19,” CEBM, March 26, 2020, https://www.cebm.net/covid-19/sars-cov-2-viral-load-and-the-severity-of-covid-19/.

[41] Think of it this way; speed limits aren’t perfect. Some people will break the law; accidents will still happen. But that doesn’t mean speed limits don’t reduce the number of accidents. In the same way, although they won’t eliminate it, mask mandates will assist in curbing the spread of Covid-19.

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Yu, Alan. “What Happens to the Coronavirus When It Gets Warmer?” Whyy, May 20, 2020, https://whyy.org/articles/what-happens-to-the-coronavirus-when-it-gets-warmer/.

Zarei, Kasra, and John Duchneski. “Coronavirus Cases Rise in States with Relaxed Face Mask Policies.” The Philadelphia Inquirer, June 24, 2020, https://www.inquirer.com/health/coronavirus/covid-19-coronavirus-face-masks-infection-rates-20200624.html.

            Zhang, Lijie, Zhibin Peng, Jianming Ou, Guang Zeng, Robert E. Fontaine, Mingbin Liu, Fuqiang Cui, et al., “Protection by Face Masks against Influenza A(H1N1)pdm09 Virus on Trans-Pacific Passenger Aircraft, 2009,” Emerging Infectious Diseaes 19, no. 9 (September 2013): 1403-10, https://doi.org/10.3201/eid1909.121765.

Thanks Petar

While I do appreciate this opportunity, I’d like to begin by expressing my reservation about participating in this debate. Anyone curious about the effectiveness of mask mandates should listen to current medical and public health experts—epidemiologists and immunologists—not a debate between a philosopher/logician and a physicist who specialized in metals but no longer works or publishes in academia.

What’s more, there is really no debate to be had on this issue. There was a debate, in the scientific community, a few months ago—but it was settled very quickly once the evidence was laid out. Indeed, initially, I thought that public mask wearing was overkill. But then I learned how COVID spreads, and how prevalent asymptomatic spread of COVID is. To help curb its spread, all masks have to do is reduce the number of infected particles that exit an infected person’s mouth—and good evidence suggests they do. Since I am willing to update my beliefs in light of new evidence, I changed my mind.

This, Petar, is why you couldn’t find any medical experts for this debate; they’ve already had it. And engaging with pseudoscientific arguments risks legitimizing them. But I engage with pseudoscience for a living. And since this is one of those times that pseudoscience can kill, I decided to take this opportunity to (1) communicate the scientific argument on this issue to a broader audience and (2) debunk the pseudoscience. Fortunately, as a philosopher and logician, who teaches and publishes on logic, argumentation, philosophy of science, medical diagnosis, and medical pseudoscience—I am especially qualified to do these two things.  

SLIDE 2

Ok, so first: how and why masks assist in curbing the spread of Covid-19.

The explanation is simple, but misinformation has confused the issue. It’s commonly believed that masks simply protect their wearer from becoming infected by filtering the air that a person inhales. But while there is some evidence that cloth masks maybe offer some protection to their wearer in this regard,[1],[2] the primary way they help mitigate the spread is by filtering the air a person exhales—by [click] sneezing, coughing, speaking, or breathing.

SLIDE 3

Why are masks effective in filtering viruses from the exhaled air? Because a virus doesn’t travel by itself; it travels in droplets of moisture propelled from the mouth that can be captured. The largest droplets are intercepted by the surface of the mask; smaller ones are stopped by impaction as they try to make it through the mask; and the smallest, including aerosols, are diffused by the mask because of something called Brownian motion–the erratic way they move. This lowers the number of infected droplets in the air, and thus reduces the risk of exposure for other people.[3] [4]

SLIDE 4

Now, it’s important to note that, while all masks filter exhalations,[5] certain kinds of masks are better than others.[6] The early woven cloth masks were effective, but not as effective as later non-woven ones—what we today call “medical” or “surgical masks.” (According to Davies (et al, 2013), while both types are effective, surgical masks are about three times more effective. [7] [8] But different kinds of cloth, layered or combined, can offer better filtration, by making the pathway particles would have to travel to get through the mask more convoluted. Aydin (et al, 2020) found that layering cotton fabrics can make homemade masks almost as effective as surgical masks,[9] and Konda (et al, 2020) found that layering different kinds of fabrics (like cotton with flannel) could also increase their efficacy.  Such masks filtered 80% of particles smaller than 300 nanometers (0.3 microns) and 90% of those larger. [10] Filters can also improve mask efficacy.[11]

SLIDE 5

Now if an infected droplet is already in the air that a masked person is about to inhale, the mask will be less likely to catch that particle. That might make one question how cloth masks can filter the air that someone exhales. But that question is easily answered. Part of it is due to air flow; when you are breathing in, you are not pushing the air directly through the mask. But also–the longer a droplet is in the air, the more opportunity it has to evaporate and become smaller (and even aerosolize)—and (unless it’s smaller than 0.3 microns) the smaller it is, the less likely a particle is to be caught by a mask.[12] So infected droplets in the air that an unmasked person has exhaled has a better chance at making it through your mask. But most of the infected droplets exiting your mouth won’t, since they have not yet had a chance to evaporate.[13] [14]

SLIDE 6

In other words, masks unquestionably filter droplets (on the right), including most of them that would become aerosols (in the middle) And they can even capture those that start out small (on the far left), just less efficiently.

So, if you are in a room with a non-masked infected person, you are pretty likely to be infected even if you are wearing a cloth mask. However, if that infected person is wearing a cloth mask, you are much less likely to be infected—even if you are not wearing a mask. This is why it is said “My mask protects you, your mask protects me.”[15] Your choice to not wear a mask does not put you at risk; it puts others at risk.

Now, since the fact that the majority of the work that masks do in curbing the spread of COVID is done by the masks that infected persons are wearing, one might wonder …

SLIDE 7

… why we don’t just have infected people wear them. Indeed, this was part of the reasoning behind the traditional ], years long, CDC and WHO recommendations that said mask wearing is not necessary for seemingly healthy individuals. With many diseases it is not. But then experts realized just how long a person could be infected with COVID without knowing it, and even that many infected never have any symptoms.[16] Consequently, public mask mandates are the only way to ensure that infected persons—including those who are pre- or asymptomatic—are wearing a mask. Such mandates would thus reduce the number of infected people without masks, thus reduce the number of infected particles in the air, and thus reduce the probability of transmission. Once we realized this, mask wearing was recommended. Granted, the CDC and WHO lagged behind the experts in this regard. But scientists change their mind based on evidence all the time. That’s not unusual. It’s just usually not that public.

SLIDE 8

So given what we know masks do, the fact that mandating them helps curb the spread of COVID is just common sense. But the evidence also bears this out. Now you can’t do a direct, controlled experiment where you blindly throw non-infected people into rooms with masked or un-masked infected persons, and see if they get sick. That’s unethical. But all the ethical ways to study this question indirectly indicate that cloth masks curb the spread.

For example, transmission rates slowed in hospitals (Sung (2016)[17] Wang, et. al., 2020),[18] German cities (Mitz, et. al 2020),[19] North Texas (Nandy, 2020),[20] and in US states (Lyu & Wehby, 2020),[21] after mandates went into effect. (In Germany, they reduced growth rates by 40%.) What’s more, U.S. States with mandates have seen much less spread than those without, [22] as have countries where mask use is popular.[23] Modeling has also confirmed the effectiveness of mask mandates.[24] According to Stutt (et. al., 2020)[25] and Eikenberry (et. al., 2020), if masks are just 50% effective, they could help bring down infection rates to non-epidemic levels and reduce the death rate by as much as 45%. Large reviews of observational and comparative studies have also concluded that mask mandates are highly effective,[26] as have collections of collaborating experts.[27] And, of course, there were those infected hairstylists in Missouri who didn’t pass it on to 140 of their clients because they were wearing a mask.[28]

The IHME found that mask mandates could save 33,000 by October 1st,[29] and (according to Brooks, 2020) if everyone worse a mask, we could get the pandemic under control in four to eight weeks.[30] None of this is as good evidence as the above described unethical blinded study would provide, but it is literally as good as one could reasonably expect.[31] Indeed, because we are not dealing with a drug, this evidence makes randomized controlled trials unnecessary.

Now, Rancourt self-published an article he titled “Masks Don’t Work” where he suggests that the science indicates otherwise—but that brings me to the second part of my opening argument: debunking the pseudoscience.

SLIDE 9

In his article “Masks Don’t Work,” Rancourt offers a survey of seven (7) studies which he says prove that “masks don’t work.” But…

First, it’s not a true survey of the literature. Rancourt just combed through studies to find the ones he thinks support his position, and ignored the rest.  In logic, we call this “confirmation bias.” At best, it only proves some people can find some evidence for anything.”

Second, the majority of the studies he cites, like Smith (et. al. 2016) are irrelevant to his claim. They are about whether N95 masks protect their wearer better than surgical masks, not about whether cloth masks filter exhaled air. So he’s equivocating on the word “mask” and what it means for a mask “to work.” What’s more, although it is very unlikely that a surgical mask offers just as much protection as (properly sealed) N95 masks[32]even if they did, that wouldn’t even prove that cloth masks can’t filter inhaled air, much less exhaled air. With all protective equipment, you are bound to reach an upper limit, where adding more protection is just overkill.

SLIDE 10

Third, the other studies he mentions simply don’t say what he claims they do. For example, his quote from bin-Reza (2012) read “None of the studies established a conclusive relationship between mask/respirator use and protection against influenza infection.” This implies that the study concluded that there is no benefit to wearing masks or respirators. In reality, however, the slash in the “mask/respirator” phrase is meant to indicate a comparison between the two—the study is actually saying that they are equally effective, not lumping them together and declaring them both ineffective. Several of the sentences before and after the one he quote mines demonstrate this. 

“Eight of nine retrospective observational studies found that mask and ⁄ or respirator use was independently associated with a reduced risk of severe acute respiratory syndrome (SARS).”

And SARS, by the way, is the most analogous disease to COVID-19.

The text accompanying the other studies contain similarly misleading quotes or summaries.  As Jacobs (2009) said to me in correspondence,

Dr. Rancourt’s opinion piece mischaracterizes the research findings I reported in my 2009 peer-reviewed article…. It was not designed to examine mask effectiveness of preventing the mask-wearer from spreading a respiratory infection. My study has no bearing on addressing that recommendation…. [and] The mask used was a typical surgical (disposable paper) mask, not an N-95 respirator mask as [Rancourt] states in his article.

And the conclusions of others just outright contradict his thesis.

“There is some evidence to support the wearing of masks or respirators during illness to protect others, and public health emphasis on mask wearing during illness may help to reduce influenza virus transmission.” Cowling (et. al., 2010)

In other words, Rancourt scoured the literature, and the best he could do is find studies that don’t actually support his thesis, but which he could misquote or mis-summarize to make it look like they do.[33]

SLIDE 11

The second argument he presents cites Shaman’s 2010 article which suggests that humidity is responsible for seasonal variation in flu infections. From this he somehow concludes that masks cannot mitigate the spread. But (1) Shaman himself has said that we don’t know enough about COVID to conclude that humidity is a factor in its transmission[34]—and the fact that COVID is spreading like wildfire in Florida and Texas in July seems to indicate that it is not. Indeed, experts agree, that with new diseases, it’s not. [35] (2) This argument relies on the assumptions that COVID spreads solely via aerosols and masks don’t prevent aerosols from existing in the air; both of these assumptions are false. And (3) humidity causing seasonal variation wouldn’t mean that masks don’t work because humidity is not the only causal factor in transmission. There also is contact and contamination; thus, measures restricting those, like masks, would mitigate spread. In my logic class, we would call Rancourt’s error here “the fallacy of oversimplified cause.”[36]

SLIDE 12

Rancourt’s third argument suggests that infected droplets are too small to be blocked by N95 respirators, much less cloth masks. But here, he is not only (1) talking about inhalation not exhalation, (2) making false assumptions about aerosols and transmissibility, and (3) fallaciously appealing to incredulity to favor dubious theories, but (4) he doesn’t understand how N95 masks work; contrary to what he claims, because of Brownian motion, N95 filters are actually more efficient at filtering particles smaller than 0.3 microns. They are not sieves. Neither are most cloth masks.[37]

SLIDE 13

Lastly, Rancourt argues that, because masks can’t guarantee 0% exposure, they are useless. But here, he not only, again, (1) misrepresents the evidence[38] (2) makes unsupported assumptions about the minimal infective dose of COVID and a mathematical error that exaggerates the infectious potency of aerosols 10-million-fold,[39] and (3) fails to recognize that symptom severity could be proportional to the amount of viral exposure[40]—but (4) his argument is a prime example of the “all or nothing fallacy.” Yes, masks would need to 100% effective to completely stop the spread of COVID—but not to slow it. By merely reducing the amount of infected droplets in public places, they reduce spread.[41] Seatbelt laws are not 100% effective; some people still speed and accidents still happen. That doesn’t mean speed limits don’t reduce accidents.

SLIDE 14: BIBLIO

Now, I do not expect any of this to have any effect on Rancourt or those in his echo chamber. They think otherwise for ideological reasons, not evidence based scientific ones. And you cannot reason someone out of a position that they did not reason themselves into. But what I have presented here is enough to convince any fair, open-minded person that, yes, indeed, public mask mandates assist in curbing the spread of Covid-19. Indeed, for them to do so, masks only need to do what we already knew they do: catch droplets. If they were unable to do this, the successful use of HEPA filters (which operate on the same principles as mask) in nearly every segment of the economy, and in your vacuum cleaner, would just be a giant coincidence. The burden of proof is thus on Rancourt to show otherwise. Needless to say, misrepresenting the scientific evidence and offering fallacious arguments does not meet that burden. 


[1] The cloth masks do somewhat filter the air we breathe in, but not enough to be effective in high risk environments. According to this article, some researchers are starting to suspect that they offer some protection to wearers in low-risk public environments, and studies to test this are hopefully coming soon. Caitlin McCabe, “Face Masks Really Do Matter. The Scientific Evidence Is Growing,” The Wall Street Journal, July 18, 2020, https://www.wsj.com/articles/face-masks-really-do-matter-the-scientific-evidence-is-growing-11595083298  On whether medical/surgical (non-woven) masks are effective at protecting their wearer in high risk environment, the evidence seems to be mixed. MacIntyre (et al., 2014) showed that, while medical (surgical) masks provided some protection to the wearer in such environments, cloth masks provided almost none. See C. Raina MacIntyre, et al. “A Cluster Randomised Trial of Cloth Masks Compared with Medical Masks in Healthcare 1Workers,” BMJ Open 5 no. 4, (2015) https://doi.org/10.1136/bmjopen-2014-006577. The results in Seto (2003) and (Nishiura , 2005) also suggested that surgical masks do work to protect health care workers.  WH Seto,et al., “Effectiveness of Precautions Against Droplets and Contact in Prevention of Nosocomial Transmission of Severe Acute Respiratory Syndrome (SARS),” The Lancet 361, no 9368 (May 3, 2003): 1519-20, https://doi.org/10.1016/S0140-6736(03)13168-6. and Hiroshi Nishiura, et al., “Rapid Awareness and Transmission of Severe Acute Respiratory Syndrome in Hanoi French Hospital, Vietnam,” Am J Trop Med Hyg 73, no. 1 (July 2005): 17-25, https://pubmed.ncbi.nlm.nih.gov/16014825/. And Zhang (2009) suggests that they can protect even the general public. Lijie Zhang, et al., “Protection by Face Masks against Influenza A(H1N1)pdm09 Virus on Trans-Pacific Passenger Aircraft, 2009,” Emerging Infectious Diseaes 19, no. 9 (September 2013): 1403-10, https://doi.org/10.3201/eid1909.121765. But then Kähler (et al., 2020) seems to suggest that surgical (or similar) masks probably don’t provide sufficient protection for the wearer against droplet infection; only property fitted particle-filtering (e.g., N95) masks can do that. But all such studies are plagued by things like recall bias.
                When it comes to protecting others by filtering the air that a person breathes out, the study found that a simple mouth and nose cover is enough. Such masks are effective at limiting droplet emission when coughing, sneezing, speaking, singing, or breathing. Face coverings significantly reduce the spread of viruses and thus public mask wearing is “a very useful contribution to contain a pandemic.”  See Christian J. Kähler and Rainer Hain, “Fundamental Protective Mechanisms of Face Masks Against Droplet Infections,” Journal of Aerosol Science 148 (2020) https://doi.org/10.1016/j.jaerosci.2020.105617.

                [2] See also Rick Kushman, “Your Mask Cuts Own Risk by 65 Percent,” UC Davis, July 6, 2020, https://www.ucdavis.edu/coronavirus/news/your-mask-cuts-own-risk-65-percent/

[3] Talib Dbouk and Dimitris Drikakis, “On Respiratory Droplets and Face Masks,” Physics of Fluids 32, no. 063303, published electronically June 16, 2020, https://doi.org/10.1063/5.0015044.

[4] Bhanu Bhakta Neupane, Sangita Mainali, Amita Sharma, and Basant Giri, “Optical Microscopic Study of Surface Morphology and Filtering Efficiency of Face Masks,” PeerJ 7,no. e7142 (2019), https://doi.org/10.7717/peerj.7142.

[5] Two more studies on mask effectiveness:
Qing-Xia Ma, et al, “Potential Utilities of Mask-Wearing and Instant Hand Hygiene for Fighting SARS-CoV-2” Journal of Medical Virology (2020) https://doi.org/10.1002/jmv.25805.

This study suggested that 95% of viruses in aerosols could be blocked by homemade masks, and 97% could be blocked by surgical masks.

Nancy H. L. Leung, et al., “Respiratory Virus Shedding in Exhaled Breath and Efficacy of Face Masks,” Nature Medicine 26 (2020): 676-80, https://doi.org/10.1038/s41591-020-0843-2.
This is a study out of Hong Kong which suggested that people wearing a mask was very effective at reducing transmission of alpha coronaviruses.

[6] Cloth masks of only one material seem to have very little effectiveness: Samy Rengasamy, Benjamin Eimer, and Ronald E. Shaffer, “Simple Respiratory Protection – Evaluation of the Filtration Performance of Cloth Masks and Common Fabric Materials Against 20-1000 nm Size Particles,” Annals of Occupational Hygiene 54, no. 7 (October 2010): 789-98, https://doi.org/10.1093/annhyg/meq044. This is why those who are just wearing bandanas, or pulling their t-shirt over their mouth, are not doing anyone any good.

[7]  Both types “significantly reduced the number of microorganisms expelled by volunteers,” the “the surgical mask was 3 times more effective.”) Anna Davies, et al., “Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?” Disaster Medicine and Public Health Preparedness 7, no. 4 (August 2013): 413-8, https://doi.org/10.1017/dmp.2013.43.

                [8] Milton (2013) found that surgical masks decreased emission of large particles by 25 fold, and aerosols by 3 fold in flu patients. See Donald K Milton, et al., Influenza Virus Aerosols in Human Exhaled Breath: Particle Size, Culturability, and Effect of Surgical Masks,” PLoS Pathogens 9, no. 3 (March 2013): 1-7, https://doi.org/10.1371/journal.ppat.1003205. 5

[9] Aydin et al, 2020, suggests that layering great increases the filtering efficiency of cloth masks while also maintaining some breathability, Onur Aydin, et al., “Performance of Fabrics for Home-Made Masks Against the Spread of Respiratory Infections through Droplets: A Quantitative Mechanistic Study,” medRxiv,preprint, submitted July 8, 2020  https://doi.org/10.1101/2020.04.19.20071779.

[10] “Overall, we find that combinations of various commonly available fabrics used in cloth masks can potentially provide significant protection against the transmission of aerosol particles.” Abhiteja Konda, Abhinav Prakash, Gregory A. Moss, Michael Schmoldt, Gregory D. Grant, and Supratik Guha, “Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks,” ACS Nano 14, no. 5 (2020): 6339-47, https://doi.org/10.1021/acsnano.0c03252.

[11] Dr. Marty, a professor of infectious diseases at Florida International University told “Good Morning America.” “But if you add that filter, then you’re also adding a really good protection for yourself.” See Becky Worley, Anthon Kane, Robyn Weil, and Angeline Jane Bernabe, “Face Masks With Filter add Another Layer of Protection, Experts Say,” GMA, July 16, 2020, https://abcnews.go.com/GMA/Wellness/face-masks-filters-add-layer-protection-experts/story?id=71811792.

[12] That’s not quite accurate. Particles around .3 microns are actually the hardest to catch. Those smaller are easier to catch because of Brownian motion. But this actually helps my thesis, so for simplicity I shall leave this nuanced point to the side.

[13] This is actually what N95 masks are for; they protect their wearer by being 95% effective at filtering the air that a person breathes in. And because they often have unfiltered exhaust vents, they usually don’t filter the air a person breathes out. Combine that with the fact that they don’t even perform their intended function well unless they are perfectly fit, and you can realize why they should likely only be worn by health care workers in high risk environments. It’s my estimation that the use of N95 masks by the general public likely wouldn’t help curb the spread of COVID-19 as well as the use of cloth masks.  But I’m happy to be corrected on that point.

[14] Some clarification here is useful. Technically, depending on how you classify “aerosoles” (definitions range from 5 microns to 100 microns), most of  the particles you breath out could be classified as arisoles–and depending on their size, the mask will filter them with different efficiencies. Even cloth masks are very good at filtering down to 10 microns, pretty good down to 5 microns, but not great below 5. Neupane, “Optical Microscopic Study of Surface Morphology and Filtering Efficiency of Face Masks.”

In one way, this is concerning because (according to Burch (2020), the average size for aerosoles leaving your mouth is 3 microns.  The good news is, despite the fact that they make up the largest number, they only represent 0.00024% of the liquid leaving your mouth during a cough. Consequently, very few of them are infected (at worst 1 out of every 700). A full “ 99.99976% of the viruses sprayed during a cough are carried in droplets — not aerosols.’) So the majority of transmission happens from droplets.  What’s more, the deadliest aerosoles are those that started out as droplets, but then evaporated down; they have higher concentrations of the virtus. Masks catch those.  Sso the inability of masks to filter out 3 micron arisles does not greatly hinder their ability to keep infected particles out of the air, and thus does not prevent them from efficiently preventing the spread of covid.
                Adrien Burch, “A Microscopic Perspective on Airborne COVID-19,” The Medium, March 31, 2020, https://medium.com/better-humans/should-you-be-worried-about-catching-covid-19-from-aerosols-6c97d023bb6d.

[15] From the abstract of: Richard O. J. H. Stutt, Renata Retkute, Michael Bradley, Christopher A. Gilligan, and John Colvin, “A Modelling Framework to Assess the Likely Effectiveness of Facemasks in Combination with ‘Lock-down’ in Managing the COVID-19 Pandemic,” Proceedings of the Royal Society A (2020) https://doi.org/10.1098/rspa.2020.0376.

[16] Wycliffe E Wei, Zongbin Li, Calvin J Chiew, Sarah E Yong, Matthias P Toh, and Vernon J Lee, ”Presymptomatic Transmission of SARS-CoV-2-Singapore, January 23-March 16, 2020,” MMWR Morb Mortal Wkly Rep. 69, no. 14 (April 2020): 411-5, https://doi.org/10.15585/mmwr.mm6914e1.

                [17]Anthony D Sung, et al. “Universal Mask Usage for Reduction of Respiratory Viral Infections after Stem Cell Transplant: a Prospective Trial,”  Clin Infect Dis 63, no. 8 (October 2016): 999-1006, https://doi.org/10.1093/cid/ciw451.

[18] Xiaowen Wang, Enrico G. Ferro, Guohai Zhou, et al., “Association Between universal Masking in a Health Care System and SARS-CoV-2 Positivity Among Health Care Workers,” JAMA,published electronically July 14, 2020, https://doi.org/ 10.1001/jama.2020.12897. In this study, cases of COVID-19 declined after mask mandates were put into effect in hospitals (that required all health care workers and patients to mask up). The study concluded that such mandates  reduce the transmission of SARS-CoV-2.

[19] Timo Mitze, Reinhold Kosfeld, Johannes Rode, and Klaus Wälde, “Face Masks Considerably Reduce COVID-19 Cases in Germany: A Synthetic Control Method Approach,” IZA (June 2020) http://ftp.iza.org/dp13319.pdf.

This study shows the impact of mask mandates in Germany. In Jena, for example, the first German city to enact such a mandate, COVID-19 cases fell by almost 25% in 20 days. The study concluded that similar mandidats could ruse the daily growth rate by 40% in the long term, although it did acknowledge that, outside Germany, different norms and climatic conditions in other countries might result in different protective outcomes.

                [20] “HSC COVID-19 Report #5 – July 20, 2020,” University of North Texas Health Science Center at Fort Worth, https://www.scribd.com/presentation/469858261/COVID-19-Report-July-20-Updated?fbclid=IwAR1ta8C-x5yYfpqQ5eghmiPFr42ndbA6rYCmTv3WbcGU9tDt3a_RU1BOIL0.

[21] In those 15 US States, they likely prevented up to 450,000 cases in under two months. Wei Lyu and George L. Wehby, “Community Use of Face Masks and COVID-19: Evidence from a Natural Experiment of State Mandates in the US,” Health Affair 39, no. 8 (2020): 1-7, https://doi.org/ 10.1377/hlthaff.2020.00818.

This was a retrospective analysis which examined the effects that different governmental orders to wear face masks had on COVID-19 growth rates, from April 9-May 15, 2020. It estimated that they prevated between 230,000 and 450,000 cases by May 22 (a reduction of 14-27%).

[22] Kasra Zarei and John Duchneskie, “Coronavirus Cases Rise in States with Relaxed Face Mask Policies,” The Philadelphia Inquirer, June 24, 2020, https://www.inquirer.com/health/coronavirus/covid-19-coronavirus-face-masks-infection-rates-20200624.html.

                [23] American Thoracic Society, “Countries with Early Adoption of Face Masks Showed Modest COVID-19 Infection Rates,” Medical Xpress, June 24, 2020, https://medicalxpress.com/news/2020-06-countries-early-masks-modest-covid-.html.

                [24] Samantha M. Tracht, Sara Y. Del Valle, and James M. Hyman, “Mathematical Modeling of the Effectiveness of Facemasks in Reducing the Spread of Novel Influenza A (H1N1),” Plos One 5, no. 2 (February 2010): 1-12, doi.org/10.1371/journal.pone.0009018.

[25] Stutt, et al.,“A Modelling Framework to Assess the Likely Effectiveness of Facemasks in Combination with ‘Lock-down’ in Managing the COVID-19 Pandemic.”

To keep the infection rate (R0) below 1.0, the authors argue for widespread use of face masks. “[F]acemask adoption by entire populations would have a significant impact on reducing COVID-19 spread.” “[I]n summary, our modelling analyses provide support for the immediate, universal adoption of facemasks by the public.”

[26] Derek K Chu, et al., “Physical Distancing, Face Masks, and Eye Protection to Prevent Person-to-person Transmission of SARS-CoV-2 and COVID-19: A Systematic Review and Meta-analysis,” The Lancet 395, no. 10242 (2020): 1973-87, https://doi.org/10.1016/S0140-6736(20)31142-9.

This was a review of 172 observational studies and 44 relevant comparative studies. The authors concluded “Face mask use could result in a large reduction in risk of infection.”

[27] Kimberly A. Prather, Chia C. Wang, and Robert T. Schooley, “Reducing Transmission of SARS-CoV-2,” Science 368, no. 6498 (June 2020): 1422-24, https://doi.org/10.1126/science.abc6197. In this paper, aerosol chemists and an infectious disease specialist argue that, because “airborne spread from undiagnosed infections will continuously undermine the effectiveness of even the most vigorous testing, tracing and social distancing programs,” the widespread use of masks are necessary to help prevent the spread of COVID. Both analytical information about the virus and information about countries where masks are commonplace was used.

Catherine M. Clase, et al., “Cloth Masks May Prevent Transmission of COVID-19: An Evidence-Based, Risk-Based Approach,” Annals of Internal Medicine, published electronically May 22, 2020, https://doi.org/10.7326/M20-2567. This study, done by an international research team of medical doctors and other medical specialists not only concluded that cloth masks worn by the public will reduce COVID-19 transmission rates, but that the benefits of widespread mask use outweigh any risks that may be brought about by wearing masks (such as improper use).

                [28] M. Joshua Hendrix, Charlse Walde, Kendra Findley, and Robin Trotman, “Absence of Apparent Transmission of SARS-CoV-2 from Two Stylists After Exposure at a Hair Salon with a Universal Face Covering Policy – Springfield, Missouri, May 2020,” Weekly 69, no. 28 (July 1, 2020): 930-32, http://dx.doi.org/10.15585/mmwr.mm6928e2external icon.

[29] “New IHME COVID-19 Model Projects Nearly 180,000 US Deaths,” IHME,June 24, 2020, http://www.healthdata.org/news-release/new-ihme-covid-19-model-projects-nearly-180000-us-deaths.

[30] For the quote, see McCabe, “Face Masks Really Do Matter.” For the evidence behind it, see  John T. Brooks, Jay C. Butler, Robert R. Redfield, “Universal Masking to Prevent SARS-CoV-2 Transmission – The Time is Now,” Jama, published online July 14, 2020, https://doi.org/10.1001/jama.2020.13107.

[31] for more such evidence, see “Face Masks – A Summary of Relevant Research Papers for COVID-19,” Sound Reason & More,June 11, 2020, https://soundreasonandmore.wordpress.com/2020/06/11/face-masks-a-summary-of-relevant-research-papers-for-covid-19/.

[32] See Sergey A. Grinshpun, et al., “Performance of an N95 Filtering Facepiece Particulate Respirator and a Surgical Mask During Human Breathing: Two Pathways for Particle Penetration,” Journal of Occupational and Environmental Hygiene 6, no. 10 (2009): 593-603, https://doi.org/10.1080/15459620903120086. See also C Raina MacIntyre, et al., “The Efficacy of Medical Masks and Respirators Against Respiratory Infection in Healthcare Workers,” Influenza and Other Respir Viruses 11, no. 6 (November 2017): 511-17, https://doi.org/10.1111/irv.12474. See also Loeb M, McGeer A, Henry B, et al. “SARS among critical care nurses,” Toronto. Emerg Infect Dis 2004 Feb;10(2):251-5.

[33] Here is a full rundown of how Rancourt misrepresents the studies he cites, and how they are either irrelevant to his thesis, or actually contradict it.

Joshua L. Jacobs, et al., “Use of Surgical Face Masks to Reduce the Incidence of the Common Cold Among health Care Workers in Japan: A Randomized Controlled Trial,” Am J Infect Control 37, no. 5 (June 2009): 417-19, https://doi.org/ 10.1016/j.ajic.2008.11.002.

This study showed that N95 masks cause headaches in some, and that (surgical) facemasks don’t protect their wearer. This only tells us what we already know: Wearing a tight banded mask on your face for 12 hours is bound to cause headache, and surgical masks don’t provide adequate protection in high risk environments. And since both findings are irrelevant to whether cloth masks filter outgoing particles, this study is irrelevant to his thesis.

B.J. Cowling, Y. Zhou, D.K.M.Ip, G.M.Leung, and A.E. Aiello, “Face Masks to Prevent Transmission of Influenza Virus: A Systematic Review,” Epidemiology & Infection 138, no. 4 (January 2010): 449-456, https://doi.org/10.1017/S0950268809991658.

The part of the study that Rancourt mentions is about whether masks (in this case, cloth masks) protect their wearer from infection, not whether they filter exhaled air and thus protect others. So it is irrelevant to his thesis. What’s more, the authors admit that the body of evidence they are examining is not sufficient to draw a conclusion, but also suggest that the evidence that does exist at least suggests that cloth masks do provide some protection for their wearer—probably not enough for a healthcare setting, but maybe enough for household use. They recommend further study on this topic. The part of the study that Rancourt doesn’t mention is the part that examines whether cloth provides protection to others by filtering air, and they conclude that they do. Rancourt is engaged in major confirmation bias here, by just leaving that part out.

Faisal bin-Reza, Vicente Lopez Chavarrias, Angus Nicoll, Mary E. Chamberland, “The use of masks and respirators to prevent transmission of influenza: a systematic review of the scientific evidence,” Influenza and Other Respiratory Viruses 6, no. 4 (December 2011): 257, https://do8i.org/ 0.1111/j.1750-2659.2011.00307.x.

As I mentioned in my opening statement, Rancourt uses a misleading quote from this one to imply that it found that “mask/respirators” don’t work, when in fact it found that they work equally well. What’s more, the part of the study Rancourt cities is about influenza, not COVID—and the authors themselves specifically state that their findings about influenza cannot be extrapolated to SARS-CoV-1 (“SARS is an unusual acute viral respiratory infection with a very different epidemiology to almost all other respiratory viral infections. It is fundamentally different from human influenza.”) But SARS-CoV-1 is very similar to SARS-CoV-2 (the cause of COVID-19), and about SARS-CoV-1 this study “found that mask and ⁄or respirator use was independently associated with a reduced risk of severe acute respiratory syndrome.”

Jeffrey D. Smith, et al., “Effectiveness of N95 Respirators Versus Surgical Masks in Protecting Health Care Workers from Acute Respiratory Infection: a Systematic Review and Meta-analysis,” CMAJ 188, no. 8 (May 2016): 567-74, https://doi.org/10.1503/cmaj.150835.

This study compares the effectiveness of N95 and surgical masks; as I explain in the main text of my opening statement, this makes it irrelevant to his thesis. What more, it admits that it doesn’t prove that they do offer equal protection; just that the available evidence so far is inadequate for proving that N95 masks offer more protection in a clinical setting. “Although N95 respirators appeared to have a protective advantage over surgical masks in laboratory settings, our meta-analysis showed that there were insufficient data to determine definitively whether N95 respirators are superior to surgical masks in protecting health care workers against transmissible acute respiratory infections in clinical settings.” However, even though it was not enough to prove they were superior, they did find that “In general, compared with surgical masks, N95 respirators showed less filter penetration, less face-seal leakage and less total inward leakage under the laboratory experimental conditions described.” So this is far from proof that N95’s don’t work better than masks.

Vittoria Offedu, et al., “Effectiveness of Masks and Respirators Against Respiratory Infections in Healthcare Workers: A Systematic Review and Meta-Analysis,” Clinical Infectious Diseases 65 no. 11, (December 2017): 1934–42, https://doi.org/10.1093/cid/cix681.

Again, this study is about whether N95 and surgical masks protect their wearer—specifically healthcare workers in high risk settings. It is not about whether cloth masks protect others by catching expelled droplets of COVID. So it is irrelevant to the issue. (It found that N95 masks do protect better than surgical masks against clinical respiratory illness, but that N95 and surgical masks protect against viral infections and influenza-like illness equally well. Rancourt takes the quote about this (“Evidence of a protective effect of masks or respirators against verified respiratory infection (VRI) was not statistically significant” out of context to make it seem like it is about the effectiveness of masks.) What’s more, it specifically found that masks and respirators do protect against SARS (which, again, is the closest thing to Covid-19). Indeed, it specifically stated that “This systematic review and meta-analysis supports the use of respiratory protection.”

Lewis J. Radonovich, Michael S. Simberkoff, and Mary T. Bessessen, “N95 Respirators vs Medical Masks for Preventing Influenza Among Health Care Personnel: A Randomized Clinical Trial,” JAMA 322, no. 9 (2019): 824–833, https://doi.org/10.1001/jama.2019.11645.

Again, this study compares the effectiveness of N95 and medical masks; as I explain in the main text of my opening statement, this makes it irrelevant to his thesis. What’s more, it’s about the flu—not SARS, so its findings really can’t be transferred over to COVID. Also, the non-difference could just be due to the N95’s not being properly sealed or used.

Youlin Long, et al., “Effectiveness of N95 respirators versus surgical masks against influenza: A systematic review and meta-analysis,” J Evid Based Med 13 (2020): 93-101, https://doi.org/0.1111/jebm.12381.

Again, this study compares the effectiveness of N95 and medical masks; as I explain in the main text of my opening statement, this makes it irrelevant to his thesis. And again, it’s about the flu—not SARS, so its findings really can’t be transferred over to COVID. It merely suggests that N95 masks should be reserved for health care workers in the most high risk situations—not that cloth masks can’t filter out droplets.

For this rundown, I partially relied on information provided here:  “Confirmation Bias Masks Truth OR Confirmation Bias, Masks, Truth,” Sound Reason & More,June 30, 2020, https://soundreasonandmore.wordpress.com/2020/06/30/confirmation-bias-masks-truth-or-confirmation-bias-masks-truth/?fbclid=IwAR38Vw0Ev6l5CU8bdn3f5uLsgPSkJErKyj07WPZiad-q0IcHxTl8mdH10o8.
                In other notes, I also relied on some information provided here: “Face Masks – A Summary of Relevant Research Papers for COVID-19.”

[34] Alan Yu, “What Happens to the Coronavirus When It Gets Warmer?” Whyy, May 20, 2020, http://whyy.org/articles/what-happens-to-the-coronavirus-when-it-gets-warmer 

                [35] Quote from: Alan Yu, “What Happens to the Coronavirus When It Gets Warmer?” Whyy, May 20, 2020, https://whyy.org/articles/what-happens-to-the-coronavirus-when-it-gets-warmer/. Here is the study: Rachel E. Baker, Wenchang Yang, Gabriel A. Vecchi, C. Jessica E. Metcalf, and Bryan T. Grenfell, “Susceptible Supply Limits the Role of Climate in the Early SARS-CoV-2 Pandemic,” Science 369, no. 6501 (July 17, 2020): 315-19, https://doi.org/10.1126/science.abc2535.   

[36] To illustrate this fallacy, imagine that we forcibly locked everyone in a separate room for two months to mitigate the spread of the flu. This would be a bad idea for multiple reasons, but that level of isolation would obviously mitigate the spread. No physical contact means no spread. But now imagine someone said, “It won’t mitigate the spread at all because humidity explains seasonal variation.” Wouldn’t we laugh them out of the room. Even if humidity is normally a major factor, that doesn’t mean physical contact is not also a factor—and so it doesn’t mean that keeping people from being in contact wouldn’t mitigate the spread. Of course it would. In the same way, so would reducing the number of infected droplets in the air with masks.

[37] Just below 0.3 microns is where Brownian Motion starts, so 0.3 micron particles are actually the hardest to capture. N95 masks are so named because they are 95% efficient at capturing such particles. They are actually more efficient at capturing particles both larger and small than that.  “N95s – Sufficient Protection for Covid19?” https://www.sphosp.org/wp-content/uploads/2020/04/Letter-in-response-to-N-95-use-RA-Final.pdf. See also Olof Gustafsson, Simon Gustafsson, Levon Manukyan, and Albert Mihranyan, “Significance of Brownian Motion for Nanoparticle and Virus Capture in Nanocellulose-Based Filter Paper,” Membranes 8, no. 4, published online October 5, 2018, https://doi/org/10.3390/membranes8040090.  

                [38] Prasith Baccam, Catherine Beauchein, Catherine A Macken, Frederick G Hayden, and Alan S Perelson, “Kinetics of Influenza A Virus Infection in Humans,” Journal of Virology 80, no. 15 (August 2006): 7590-9, https://doi.org/ 10.1128/JVI.01623-05 and Christopher B Brooke, William L Ince, Jens Wrammert, Rafi Ahmed, Patrick C Wilson, Jack R Bennink, and Jonathan W Yewdell, “Most Influenza A Virions Fail To Express at Least One Essential Viral Protein,” Journal of Virology87, no. 6 (March 2013): 3155-62, https://doi.org/ 10.1128/JVI.02284-12 They only talk about how quickly or efficiently viruses reproduce in cells once they are infected–not the probability of cells becoming infected once exposed.

[39] What’s more, he makes a mathematical error that greatly overestimates how many viruses would be in an aerosolized droplet. He says that “there are 1000 to 10 million viral particles, in each microdroplet 1 to 10 microns in size.” But, in fact, microdroplets of that size are mostly empty of virus and contain at most a single viral particle. Why? Because it’s difficult to get coronavirus into a concentration much higher than 10 million per mL (plaque forming units per milliliter)[39]; and a 10 micron droplet is (4/3 * 5^3 * 10^-18 m^3 =) 0.167 picoliter. A ml is 1 billion picoliters. So for every 1,000 10 micron droplets, only at most 2 (1.67) will have even a single virus in it—that’s roughly 1 out of every 600. So he is making an mathematical error of a factor of at least 10 million here. (My thanks to MW and my wife for the math!) And since it is far from established that one virus is sufficient for an infection, much less a severe on, his argument here is based on nothing. Source: Yinon M Bar-On, Avi Flamholz, Rob Phillps, and Ron Milo, “SARS-CoV-2 (COVID-19) By the Numbers,” eLIfe 9, no. e57309, published online April 2, 2020, https://doi.org/10.7554/eLife.57309.  

                [40] Carl Heneghan, Jon Brassey, and Tom Jefferson, “SARS-CoV-2 Viral Load and the Severity of COVID-19,” CEBM, March 26, 2020, https://www.cebm.net/covid-19/sars-cov-2-viral-load-and-the-severity-of-covid-19/.

[41] Think of it this way; speed limits aren’t perfect. Some people will break the law; accidents will still happen. But that doesn’t mean speed limits don’t reduce the number of accidents. In the same way, although they won’t eliminate it, mask mandates will assist in curbing the spread of Covid-19.

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