Do Masks Work During the Pandemic? Scientists Say “Yes.” Secondary Reviews of Clinical Trials Say “No.” So, Which Is It?

Yves here. Many of you may recall that Yaneer Bar-Yam and Nassim Nicholas Taleb, who are two of the four authors of a paper on the considerable and wide-ranging analytical/statistical defects in the infamous anti-mask Cochrane Report. were, along with Jospeh Norman, very early to warn (January 26, 2020) that Covid-19 had the potential to become a pandemic. The possibility of a Seriously Bad fat-tailed outcome meant aggressive action was the rational response. The fact that Covid-19 was a pandemic was not acknowledged by health officials until March. Norman, Bar-Yam and Taleb stressed:

Together, these observations lead to the necessity of a precautionary approach to current and potential pandemic outbreaks that must include constraining mobility patterns in the early stages of an outbreak, especially when little is known about the true parameters of the pathogen.

It will cost something to reduce mobility in the short term, but to fail do so will eventually cost everything—if not from this event, then one in the future

Biomedical scientist GM similarly had argued it would have been possible to contain the spread of the wild type Covid, which was much less transmissible than later variants, if officials had acted aggressively and early when the total number of infected was less than enormous and contract tracing also would have been viable. But that small window for effective action was lost.

As we see regularly, far too many have rubbished another important risk-reduction strategy, masking. The fact that wearing a maks to prevent contagion is considered polite in Japan and Southeast Asia and is separately often used as a response to poor air quality likely goes a long way in explaining much lower Covid infection rates in those regions versus, say, the Anglosphere. Lambert looks to be on to something when he keeps muttering about democidal elites….

By KLG, who has held research and academic positions in three US medical schools since 1995 and is currently Professor of Biochemistry and Associate Dean. He has performed and directed research on protein structure, function, and evolution; cell adhesion and motility; the mechanism of viral fusion proteins; and assembly of the vertebrate heart. He has served on national review panels of both public and private funding agencies, and his research and that of his students has been funded by the American Heart Association, American Cancer Society, and National Institutes of Health.

Forty years ago when I was an apprentice scientist, the HIV/AIDS epidemic brought out much of the best in biomedical science: Good thinking, cooperation, and collaboration.  It also brought out some of the worst, as competing research groups raced to discover the cause of a horrific disease that was relentlessly killing healthy young men, mostly in the Global North, which is where such things get noticed first.  Genuine progress was made fairly rapidly even so, and every week Nature, Science, and Cell contained the latest research which we read one after another in the lab.  The latest HIV/AIDS evidence was a staple of Journal Clubs across the world.

Nevertheless, politics and so-called “special interests” got in the way, as they always seem to.  But within a few years HIV was identified as the cause of AIDS.  It is only a slight exaggeration to say that today the only factor standing in the way of worldwide use of effective anti-HIV therapy is money.  How to prevent the spread of HIV through behavioral interventions is not a matter of dispute.  If one wants to read the “other side of the AIDS story,” Celia Farber’s Serious Adverse Events: An Uncensored History of AIDS has recently been re-issued by Chelsea Green.  A new copy sits on my table, and I look forward to re-reading it.  There could be valuable lessons in there somewhere that are valid today.  If so, I will let you know.

When what became known as COVID-19 appeared in Wuhan in late 2019, the cause of this respiratory disease was identified within weeks (this progress can be easily measured in days if one so desires).  Such has been the acceleration of data accumulation in modern molecular biology and medicine.  What took years when I was that young apprentice can now be accomplished in hours.  Of course, that SARS-CoV-2 had precedents in the original SARS and MERS outbreaks helped.  Which brings us to the question, “How do you stop the spread of a respiratory disease?”  Although there was much hygiene theatre during the early days of COVID-19, that SARS-CoV-2 is airborne was obvious from the beginning of the current pandemic.  This does not mean that frequent hand washing isn’t a good idea, fomites do indeed spread contagion. And when something airborne is spreading and can cause disease, masks are likely to work.  Even relatively inefficient masks such as blue surgical masks can work at low viral loads when everyone wears them, another social and behavioral intervention that restrains an epidemic.  Examples from the primary literature supporting mask usage rather than the secondary review literature are considered below.

Although this seems to have been largely forgotten, the use of masks during a pandemic has a an old history, as shown in a remarkable photograph of spectators in Grant Field in Atlanta during the 1918 football game between Georgia Tech and Furman.  And masks were not the only intervention recommended:

At Tech, in fact, masks weren’t the only precaution taken. The Oct. 10 edition of the (Atlanta) Constitution apprised readers of another measure ordered by army medical authorities at the school to prevent the spread of the contagion at football games – no cheerleading…“Cheering is too much like sneezing: if it is to be done in these days of influenza, it should be done through a handkerchief, and a cheer through a handkerchief would not be worth doing,” writer J.H. McKee reported. “So there will be no cheerleading.”

All in all, eminent good sense!  Did the masks work?  No one can know today, but the engineering approach to prevention of the spread of a putative airborne contagion was an obvious intervention, at what was to become a leading engineering institution.  However, as noted in this article by Ken Sugiura, local politicians demurred.  Bans on gatherings were soon discontinued, and the death rate from the so-called Spanish Flu was about the same in Atlanta as everywhere else.  That result might have been different.

Early in the current pandemic several well done theoretical and practical studies showed that masks are effective in preventing spread of disease, but this was not and has not been generally appreciated.  The reasons are many and varied.  The Cochrane Study on Physical interventions to interrupt or reduce the spread of respiratory viruses (Review), published on 30 January 2023, has received much attention.  The interpretation of the Cochrane Review was that “masks do not work.”

Is this true?  “No” is the conclusion of the paper Quantitative Errors in the Cochrane review on Physical interventions to interrupt or reduce the spread of respiratory viruses, recently published by Yaneer Bar-Yam, Jonathan M. Samet, Alexander F. Siegenfield, and Nassim N. Taleb (thanks to LS for sending this to me).

Before going further, it is important to note this paper is a preprint, which means it has not been peer-reviewed [1].  I usually wait until a paper has been published after peer review, but for me this is an exception that proves the rule for several reasons.  The paper is well written, and the evidence supports its conclusions.  Plus, the subject is very topical.  The consensus among the public and our political and healthcare authorities is that COVID-19 is basically over.  While COVID deaths have declined even as recordkeeping has become hit and mostly miss, this is also due to better clinical management of the disease.  Given that long COVID is common and that current vaccines prevent neither disease nor its transmission, COVID-19 is still here, perhaps to stay for a very long time.  Thus, it behooves all of us to avoid it.  Masks, distancing, and improvements in ventilation and airflow, each an engineering approach, work, whatever the continuing biological and epidemiological course of COVID-19.  So will antivirals, which to date have had an undistinguished impact on the pandemic.

This paper is also written by four scientists who have the expertise to interpret the Cochrane Review in detail.  Still, arguments from authority can be misleading or frankly disingenuous.  However, those with demonstrated authority in the subject, in the absence of conflicts of interest, should not be ignored, especially in a continuing crisis.  I am not familiar with the work of the first three authors, but Nassim N. Taleb has demonstrated repeatedly that he is qualified to dig into the details and assumptions of the Cochrane Study.  Yes, he can be controversial.  But so are Michael Mann and James Hansen and Richard Lewontin, who have also been proven correct in their areas of expertise.  Of the former, I plan to contribute something soon in this space.  Of scientists (frequently biologists) whose expertise is not “infinitely” extensible, a note is here [2].  Scientism is not so nebulous a concept when authority in one discipline does not actually translate intelligently and intelligibly to another.  This is frequently the case.

The article by Bar-Yam et al. notes that even though masks and respirators have proven their utility as an engineering solution to the problem of airborne pathogens and contaminants:

(S)tudies on their adoption over the last several decades in both clinical trials and observational studies have not provided as clear an understanding.  Here we show that the standard analytical equations used in the analysis of these studies do not accurately represent the random variables impacting study results.  By correcting these equations, it is demonstrated that conclusions drawn from these studies are heavily biased and uncertain, providing little useful information.  Despite these limitations, we show that when outcome measures are properly analyzed, existing results consistently point to the benefit of N95 respirators over medical masks, and masking over its absence.

The mathematical expressions used in this paper are complex, and it has been a long time since I used anything remotely similar.  But after several weeks with them, off and on, they do make sense to me.  The authors show that:

(T)he analyses of randomized clinical trials are missing six things: (1) propagation of uncertainty from improperly neglected random variables, (2) compounding of effects due to unaccounted transmission and infection of non-study participants, (3) invalid correspondence between study question and design reflected in variables used, (4) analysis of significance—the meaning of the results through their implications for health, (5)invalid categorization of data associated with study conditions, and (6) clear definitions and characterization of adverse effects. Using two recent reports—a trial and a systematic review and meta-analysis, we show that studies comparing N95 respirators and surgical masks, while interpreted as showing equivalency, are compatible with a substantial benefit of N95s.

These are strong conclusions and I await formal publication and subsequent discussion in the literature.  Conflation of surgical masks with N95 respirators has been common in the underlying trials, with inexact comparisons among who was wearing which masks where.  These things matter.  Other sources of data and reasoning from the engineering perspective have also been largely ignored in the typical mask trial.  These include several strong papers from early in the pandemic that were mentioned above (all are open access) briefly summarized here:

(1) Quantitative modeling of the impact of facemasks and associated leakage on the airborne transmission of SARS-CoV-2The results from different scenarios show that all the modelled facemasks provide a significantly higher protection when used as a source control rather than as a respiratory protection.  FFP (filtering facepieces) masks have a higher filtration efficiency than surgical or community masks and provide a better protection if they are fitted accordingly to minimize the leakages.

(2) Unmasking the mask studies: why the effectiveness of surgical masks in preventing respiratory infections has been underestimated (Siegenfeld, Bar-Yam, and Taleb are authors of this paper): When the adherence to mask usage guidelines is taken into account, the empirical evidence indicates that masks prevent disease transmission: all studies we analysed that did not find surgical masks to be effective were under-powered to such an extent that even if masks were 100% effective, the studies in question would still have been unlikely to find a statistically significant effect.

(3) Face masks effectively limit the probability of SARS-CoV-2 transmission: We show that variations in mask efficacy can be explained by different regimes of virus abundance and are related to population-average infection probability and reproduction number.  For SARS-CoV-2, the viral load of infectious individuals can vary by orders of magnitude (factors of 10).  We find that most environments and contacts are under conditions of low virus abundance (virus-limited), where surgical masks are effective at preventing virus spread. More-advanced masks and other protective equipment are required in potentially virus-rich indoor environments, including medical centers and hospitals.  Masks are particularly effective in combination with other preventive measures like ventilation and distancing.

(4) And from a paper published just after the first lockdowns of the pandemic (April 2020), Respiratory virus shedding in exhaled breath and efficacy of face masksWe identified seasonal human coronaviruses, influenza viruses and rhinoviruses in exhaled breath and coughs of children and adults with acute respiratory illness.  Surgical face masks significantly reduced detection of influenza virus RNA in respiratory droplets and coronavirus RNA in aerosols, with a trend toward reduced detection of coronavirus RNA in respiratory droplets (note the double emphasis about aerosols, in May 2020).  Our results indicate that surgical face masks could prevent transmission of human coronaviruses and influenza viruses from symptomatic individuals.

None of these papers is perfect, but few scientific papers are.  The only “perfect” paper I have ever read or taught was a single page (pdf) published 70 years ago that led to a Nobel Prize nine years later (thanks to The Rev Kev for finding this free version in a comment here).  Each of these four reports is a peer-reviewed paper in the primary literatureand each has a clear result: Masks prevent transmission of respiratory viruses.  Other papers in the primary literature show the same thing.  No randomized clinical trials of masks were ever needed, except to pad the bibliographies of the authors who published the papers.  It follows that no large-scale, secondary review by Cochrane of the more than 60 papers (with more excluded from the analysis) of masks was ever necessary.  But this is the way of Evidence-Based Medicine.  Those of us in the biomedical science and medical education communities can think better and do better.  And doing better is not HICPAC!  HICPAC is Big Biomedicine, where something other than biomedical science, health, and wellbeing always dictates public practice and private and especially “non-profit” gain.

After the Cochrane Report was criticized in the media the authors denied ever saying that masks do not work.  As the indispensable Naomi Oreskes explained a few weeks ago in a short piece at Scientific American:

The group’s report was published by Cochrane, an organization that collects databases and periodically issues “systematic” reviews of scientific evidence relevant to health care.  This year it published a paper addressing the efficacy of physical interventions to slow the spread of respiratory illness such as COVID.  The authors determined that wearing surgical masks “probably makes little or no difference” and that the value of N95 masks is “very uncertain.”

The typical journalistic shorthand was the cause of some of this controversy, led unsurprisingly by Bret Stephens of The New York Times.  As Oreskes points out, “the report did make clear that its conclusions were about the quality and capaciousness of available evidence, which the authors felt were insufficient to prove that masking was effective…still the authors were also uncertain about that uncertainty, stating that their confidence in their conclusion was ‘low to moderate.’”  To the contrary, the quality of the evidence that masks work is high and more than capacious enough.  But masks do require effort and imply, among other things, that interior air quality must be addressed to prevent SARS-CoV-2 (and other respiratory pathogen) transmission.  That would be expensive.

Oreskes also notes “the study’s lead author, Tom Jefferson of the University of Oxford (also the academic home of William MacAskill, of Effective Altruism and Longtermism fame) promoted the misleading interpretation.  When asked about different kinds of masks, including N95s, he declared, ‘Makes no difference—none of it’… he called mask mandates scientifically baseless…Jefferson has claimed that COVID policies were “evidence-free.”   This highlights a second problem, which is “the classic error of conflating absence of evidence with evidence of absence. The Cochrane finding was not that masking didn’t work but that scientists lacked sufficient evidence of sufficient quality to conclude that they worked. Jefferson erased that distinction, in effect arguing that because the authors couldn’t prove that masks did work, one could say that they didn’t work. That’s just wrong.”

Yes, it is wrong.  And this approach always ignores evidence on the ground.  This is the original sin of Evidence-Based Medicine and Big Biomedicine.  Again, from Oreskes:

In fact, there is strong evidence that masks do work to prevent the spread of respiratory illness. It just doesn’t come from RCTs.  It comes from Kansas.  In July 2020 the governor of Kansas issued an executive order requiring masks in public places.  Just a few weeks earlier, however, the legislature had passed a bill authorizing counties to opt out of any statewide provision.  In the months that followed, COVID rates decreased in all 24 counties with mask mandates and continued to increase in 81 other counties that opted out of them.

This evidence is “anecdotal” and thus unscientific, not to mention lost down the memory hole.  Although such evidence fits with one proven engineering solution to COVID-19, it is ignored due to what Oreskes has called “‘methodological fetishism,’ which occurs when scientists fixate on a preferred methodology and dismiss studies that don’t follow it…By dogmatically insisting on a particular definition of (often merely statistical) rigor, scientists in the past have landed on wrong answers more than once.”  The original eugenics movement made possible by the statistics of Francis Galton, Karl Pearson, and R.A. Fisher comes to mind.  And they/we will continue to do so as long as an obscurantist scientism fueled by conventional frequentist statistics reigns over science, in a world in which statistical significance very often has no clinical or other relevance whatsoever.  Correlation coefficients and p-values often obscure more than they reveal.

We must and we can do better.  Sooner rather than later.


[1] Peer review is a fraught practice these days and is no guarantee, previously covered here.  But it does matter, and science will either return to something of a golden age or continue its slipshod descent into pay-to-publish-peer-reviewed irrelevance.

[2] As a biologist, I have often read the work of others who have had large impacts in areas outside of their expertise.  The late E.O. Wilson is perhaps the most well-known among these eminent scientists whose impacts outside of his expertise have not withstood scrutiny.  Wilson was unquestionably a towering scientist.  He knew ants!  His The Theory of Island Biogeography, which was written with Robert MacArthur, is justifiably a classic that among other things introduced r/K selection theory [many offspring/minor parental effort (rat) versus few offspring/major parental investment (primate)].  From this work to Sociobiology: The New Synthesis, On Human Nature, and Genes, Mind, and Culture is a long stretch.  The tiresome Sociobiology Debate lingers, and the 50th anniversary (2025) of Wilson’s great book but for the final chapter, should be interesting.  On Human Nature is still sometimes read.  Genes, Mind, and Culture: The Coevolutionary Process deservedly sank without a trace.  Wilson’s appreciation of human impacts on the ecosphere has been important, but the impression left by this work is that he was more interested in cataloging biodiversity that will be lost in the current great extinction rather than preventing it.  Darwin’s four major works in one volume edited by Wilson is outstanding and the one source for Charles Darwin in content and presentation.  Consilience was a disjointed mess and not an improvement on the original work of a previous polymath, W. H. Whewell.  Wendell Berry took Wilson to task on consilience in an interesting response.  Other evidence regarding Wilson’s interests and putative motivations regarding sociobiology (high NYRB paywall) have recently come to light.

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  1. John R Moffett

    I can attest to the fact that peer review is broken. I have some hope that open peer review, like that found at journals such as the Frontiers series, might be a way forward, but that has it’s own problems. The old, snail-paced anonymous peer review process is dysfunctional, and needs to be replaced.

    It seems completely obvious that reducing aerosols coming from people’s breath would reduce the amount of virus in the air, and that should translate to reduced transmission. But now that this is a political issue, resolution is unlikely.

    1. GM

      That this — whether masks work — is even being discussed is on its own a damning testament to how broken modern science is.

      It is a classic tactic — let’s create the appearance of lively scientific debate in order to create a defense for the indefensible and then get our way.

      And it works because people play the game.

      If “masks don’t work”, there is an immediate and direct corollary — BSL regulations are obsolete and should be abolished, And everyone should be able to work with Ebola, smallpox, anthrax and whatever else they wish with zero safety precautions. Because masks, PPE and various other airborne precautions are what those BSL standards consist of. And if masks and PPE don’t work to stop SARS-CoV-2, and if we are not going to have them even in hospitals, then why have stringent biosafety in the lab? Right? Right?

      It follows logically. Either PPE works everywhere or it doesn’t work anywhere.

      Any takers on that proposal?

      1. Acacia

        And as one person on Twitter put it:

        I think if surgeons just wipe their hands on their shirts we should be good to go.

      2. steppenwolf fetchit

        Perhaps that proposal should be limited and restricted to those people who in this context say that ” masks don’t work”. If anyone working with Ebola, smallpox, anthrax and whatever else and using all the air-filtration and exclusion and etc. precautionary technologies that they use is caught saying that “masks don’t work” in the covid context, those persons should be forced at gunpoint to do their work with Ebola, smallpox, anthrax, etc. without a single one of the safety technolgies they currently use, in special dedicated anti-safety facilties built just for them.

        Let them live out the meaning of their own beliefs.

      3. Olivier

        Very tendentious comment. People in BSL-4 labs (the kind required to work on pathogens like Ebola) do not wear masks but hermetically sealed positive pressure suits.

        And air filtration is also different from mask wearing.

        1. Basil Pesto

          N95 respirators are part of the suite of protections adopted by the BSL system. A quick search turned up this document from the University of Pittsburgh from 2017, for example. It applies to BSL3, which is the standard used for studying sarbecoviruses like SARS2. See section 5:

          The University of Pittsburgh requires that all individuals must wear approved respiratory protection at all times while in research facilities operating at BSL-3.

          Approved respiratory protection includes respirators rated at N-95 or greater (or a PAPR)

          PAPRs where available seem favoured but N95 use in BSL3 labs is clearly well established.

          See also here



          or here, to take a few examples highlighting longstanding use of N95s in the BSL system from a rudimentary search

          and tell me again who’s being tendentious.

    2. ChiGal

      it is surprising to me to see the emphasis on surgical masks as effective, albeit less so than respirators.

      It has been my practice to eschew the “baggy blues,” as Lambert would say. But sounds like in some indoor environments the viral load is low enough that they provide sufficient benefit?

  2. Cassandra

    An (unscientific) anecdote: Several years ago, when Yaneer Bar-Yam’s name started to pop up on articles about COVID, it rang a bell for me and I had to go check. Yes, he was the guy I remembered from a study group decades ago in grad school. I have forgotten everyone else in that group, but I remember Yaneer. He was the youngest in the group but easily the leader because he was brilliant. Not necessarily relevant to the man and scientist he became, but if he makes a mathematical argument, I will listen respectfully.

    1. dave -- just dave

      As a grad student at Johns Hopkins School of Public Health, back in the 20th century, I was a research assistant for Jonathan Samet. It was a project modeling PM10 emissions from a proposed power plant in Washington state. He was a brilliant, hardworking, and humane man, working in what I now see as a relatively toxic atmosphere of competition taken to the backbiting extreme. I didn’t finish my degree there, and perhaps I am being unfair to the SPH – and this was so long ago that the name hadn’t yet been sold to a billionaire philanthropist.

    2. GM

      Unfortunately, he has made a fool of himself with obviously faulty argumentation on numerous occasions during the pandemic.

      His heart is in the right place and on balance he has done more good than bad, but that no so pleasant truth has to be acknowledged.

      The old adage remains true — the first rule to follow in science is that you should never fool yourself but you are also the easiest person to fool.

      1. dave -- just dave

        Could you be more specific? Samet and I went our separate ways long ago – for example, I did not know he became dean of the Colorado School of Public Health in 2017, from which he recently retired, and where the governor called him “Colorado’s Dr. Fauci” – no doubt intended as a compliment. What would you characterize as clear examples of the times he has fooled himself?

        1. Basil Pesto

          I think GM is referring to Bar Yam although in that case I am also curious what GM is referring to specifically

  3. Pat

    Anecdotes. Friend told me that several teachers at her school were masked yesterday. People were coughing in their classrooms and they weren’t getting sick for the holiday. Another friend was telling me about going to a performance by a niece which involved travel on public transportation as well as the crowded theater. The one thing they came away with “always take a mask” since they came back with a ‘cold’.
    People may not want to worry about Covid or mask continuously, but deep down a lot of them know masking works.

  4. .Tom

    As with so many of the fake news stories we’ve been dealing with in recent years, it is exhausting work to deal with them. This article demonstrates the principle that a lie can travel around the world while the truth is still putting on its shoes.

    It takes so much work to explain the truth in the face of a widespread lie and I often find myself at a loss to know how to talk to people about the facts of these matters.

    Thanks to KLG for doing the work here and writing up the conclusions. I find it useful.

    We have the sense that the number of people using masks in the supermarket has increased recently, albeit from a tiny fraction to a larger but still very small fraction.

    1. GF

      We were in a crowded Trader Joe’s Monday and we were the only two in the store (both customers and employees) who were wearing masks.

      1. JBird4049

        Same, but add two-three more, with one of those employees being a chin wearer in a store fairly packed. If one is going to be the odd one in wearing a mask, I would think that he would cover his nose.

        Since masking even with a cheap surgeon’s mask has some benefit, which has been accepted since the 19th century, I have to think that the writers of the Cochrane Report are bald-faced lying weasels. I am assuming that they are mercenaries in it for the money from someone else. Unless they are like those doctors and nurses who have been serial murderers for the thrill of it.

        Either way, it is extremely uncomfortable for me to read about all this and realize that legally they are going to escape any punishment for the deliberate murder of many people. More murders than even the most prolific serial killers.

        What is even worse is the acceptance that not masking is the right thing to do. What is the harm in masking aside from the annoyance especially when thinking of the likely benefits?

        1. steppenwolf fetchit

          Perhaps the “bald-faced lying weasels” were/are Jackpot Design Engineers, doing their best to spread covid as far and wide as they can deliberately on purpose.

  5. Lex

    It amazes me that a while field of practical science has been so studiously ignored throughout Covid. Industrial Hygiene (or Occupational Health) has had basically all the answers to this from the beginning, and it’s why industrial hygienists are the ones called in to design ambulance modifications in potential Ebola outbreaks. The whole field is about human exposure to contaminants (chemical, physical or biological).

    I would like to point out that masks are not an engineering solution, they are personal protective equipment. Engineering solutions are CR boxes and managing contaminants through ventilation while administrative approaches include limiting the number of people in an area.

    In most cases, respirators are used to protect the wearer and they’re the last line of defense. That is, you implement engineering controls and administrative controls to reduce the concentration of the contaminant to the lowest possible levels and use respirators for the “last mile”. This is because respirators are never 100% effective and are dependent on how they’re worn. (All respirators are labeled with a protection factor, that number is the percent inside/outside comparison. So a respirator with a PF of 10 means that concentrations inside the mask will be 10% of concentrations outside the r mask.)

    In a pandemic with an aerosol virus it’s more complicated because everyone being protected is also a potential source of the contaminant. Masks then do double duty in that they can limit the spread from a person as well as limit a non-infected person’s exposure. N95’s do this because exhalation is through the filter. True respirators with an exhalation valve do not because the exhalation valve is unfiltered. (However, the air inside the mask tends to be like 100% humid and all that water vapor will encapsulated and knock down some percent of aerosol particles in the breath, trapping them in the face piece.)

    The effectiveness of masking during Covid is not a simple, one way calculation. Because everyone in a space is a potential Covid source and the mask both protects the wearer and reduces the airborne viral load in the air, the effectiveness of masking only comes from maximum adoption in whatever the population is. So if there are 100 people in the room and they’re all wearing masks, masks will be very effective. The masks reduce the airborne concentration, which makes the masks more effective for those not infected. But as soon as you start seeing that population reduced to 99 wearing a mask, it all gets much more complicated.

    But all this misses the point of control to some degree. Everyone mask up and limit concentrations of people indoors would have been response step one. Because it’s an emergency. Response step two needed to be actual engineering controls like ventilation and filtration because those most reliably reduce the concentration of virus in the air. And then you can look again at administrative controls and masking. You need the engineering controls (and administrative controls) to maximize the effectiveness of masking, especially if you cannot guarantee everyone masking.

    There is a reason the OSHA hierarchy of controls is the inverted triangle that it is and PPE is at the bottom. A virus complicates the approach (so many potential source points) but doesn’t negate it. It’s funny and telling that throughout this I haven’t heard “and here’s an industrial hygienist to help explain this” or we’ve got industrial hygienists working on this, although the studies about filtration and virus dispersion etc have all been performed by IH scientists because that what they do.

    To be fair, I know a lot of industrial hygienist and not a few of them ignored their education and experience when it came to Covid.

    1. PlutoniumKun

      I think a lot of it comes down to power dynamics within expert groups. Technical experts/engineers rarely get a look in when doctors and medical science dominates a public health question. The irony of course is that pretty much everyone accepts that the great urban health crises of the 18th and 19th centuries were largely fixed by engineers (clean water and sewerage, and later, air pollution control), not doctors or bioscience. I’ve often thought that the success stories of antibiotics and early vaccines (especially polio) were a double edged sword, in that they shifted the focus in public health from prevention at source to cures or prophylactics. Another key issue is that after a generation or so of doctors, the hard earned lessons of TB have been forgotten. I recall an uncle who served in the Royal Merchant Marine during WWII telling me that he had been severely disciplined for the crime of leaving out his laundry to dry in the crew sleeping quarters – it was recognized that increasing humidity in sleeping areas encouraged TB spread.

      I did have hope that in China, where engineers still generally make the big decisions and doctors/academic scientists don’t have quite the status as in the West, they could change the dynamic. But unfortunately I think that the same forces are at work there – the climbdown from zero covid and subsequent gaslighting has been as complete there as in the West and elsewhere. Only Japan/ROK/Taiwan still seem to have an overt focus on masking and air contamination, even if its fading.

    1. bold'un

      I agree! Also masks don’t make you immune, they only reduce probability of infection; i.e. if I have 98% probability of escaping infection every time I meet a virus unmasked, or 99% probablilty if I meet with masked people, then someone whose lifestyle gives them a 50% of chance of catching the virus by January unmasked, should expect a 50% chance of catching it by March when masked. As the saying goes masks flatten the curve…

    2. GM

      the optimal solution for each individual is not to wear an uncomfortable mask.


      How does that follow given the consequence of infection?

      Serious PPE protects well even when you are the only one with it.

        1. ambrit

          Which brings up the question of exactly which “society” the Jackpot Engineers serve?
          The questions concerning parasites and hosts are of paramount importance here. How much of the “host” population can die off before the parasite class becomes similarly afflicted? To apply a simple geometry example, as the base of a pyramid shortens, the height of the structure shrinks proportionally. At some point, if the angle of repose of the structure’s sides steepens, in an attempt to maintain ‘height,’ the stresses ‘degrade’ the structure; the pyramid collapses.

    3. Revelo

      Not just uncomfortable but also dangerous, because of how N95 masks can increase CO2 levels. Probably not a big issue if the N95 mask is worn briefly, such as 5 minutes to transit from outdoors to room via crowded elevators. But a major issue if the mask is worn for extended periods. Anyone needing to be masked all day needs a much better solution, with builtin CO2 monitor and probably electro-mechanical pump to push air though the filter, since lung pressure alone is insufficient.

      1. Basil Pesto

        It’s amazing how N95s have been used for prolonged durations in industrial applications for decades prior to 2020 and this preposterous nonsense about dangerously high CO2 levels has only gained traction now that the civilian population has been encouraged to use them to break chains of transmission of dangerous infectious disease. Just astonishing.

  6. Jack

    I recently attended a conference in Las Vegas and from there a week long vacation in Hawaii. So I was around a lot of people and on an airplane. A lot. Hardly anyone wore masks. I would guess less than 1%. I didn’t. I am retired but my part time job is acting as a wedding officiant, so there too I am around large groups of people almost every weekend. At weddings, no masks, none, not even on the elderly. My solution to protect myself has been the judicial use of iodine nasal spray (Nasomin) and gargling (Scope). I can thank NC for introducing me to both of those prophylactics.

  7. GlassHammer

    “A brand new scientific study says X totally changes the Y for you.” has been one of the most common place stories in western media for decades and it has taught the public to lump any/all scientific data into the category of “useless trivia”.

    Add to the saturation of scientific headlines an increased frequency in their debunking along with an increase in how niche their impact often is and you get a public that just hates the label of “science”.

    This is why “masking is good for you” failed before it even started. The public was trained long ago to ignore its justification.

  8. eg

    “That would be expensive” is the essence of refusal to acknowledge that Covid is airborne. Not far behind is “that would be inconvenient” which is presumably the bucket into which a desire to obfuscate the effectiveness of masks goes, since the expense is comparatively trivial.

    So, back to the two rules:

    1. Because profits
    2. Go die

    1. steppenwolf fetchit

      There needs to be a simple way to express the rule which CDC, WHO, etc. seem to have been using to guide their attempts to suppress information about the airborne nature of covid and to suppress its expression and release even unto this very moment.

      Some simple two rules expression like . . .

      1. Because Jackpot
      2. Go kill.

      1. ambrit

        Don’t forget the forces of the Anti-Jackpot.
        1: Because Elites
        2: Spread the pain
        This has the potential to become a Great Leveling.

  9. The Rev Kev

    With masks I suppose that it all comes down to the precautionary method which started to get mentioned here back in early 2020. People wear masks in Asia as it is a cheap form of protection during their flu season and in 2020 it was noted that the Chinese in Sydney’s China Town were quick to adopt face masks while everybody else were wondering why they were doing that. It took a coupla months for everybody else to catch on why, not helped by the medical establishment warning people that wearing masks could be dangerous, just like was done in the US. Even though I have been slacking off lately with masks, there are two places where I will absolutely wear one – in doctor’s surgeries and in hospitals. Why? Because that is where sick people gather and as it turns out tomorrow I have to visit one of them. But it still angers me that so much got broken in this pandemic like trust in medical authorities, public health, peer reviews and everybody was thrown on their own resources as far as their health was concerned. I just hope that the economy i going well. /sarc

  10. Societal Illusions

    It makes sense to be overly cautious when there is little data to determine what is dangerous or not. Once data is available, decisions can be made
    with more certainty. I was going to share PANDA data about outcomes but there is a larger more macro conversation it seems:

    I am moving towards the idea that our current mechanism of understanding disease may be incorrect or at best incomplete. The assumptions we seem to make are quite broad, and the number of exceptions are too great to be ignored.

    What if… the usual understandings of the mechanics of virology are wrong?
    What if… our bodies seeking balance and removing toxins and poisons or dealing with deficient nutrients or environmental situations better explain how sickness and disease operate?
    What if… every symptom is an expected response to seeking homeostasis?

    How little we know about our bodies and how they function, even as we clearly learn more and more about specific pieces of the chemical processes involved. We may be ascribing fire to a virus that infects wood and results in burning (clearly a chemical process that seems somewhat magical).

    I don’t know that terrain theory better explains this mechanic or whether our accepted germ theory holds all the truth, but like in so many areas where one takes a deeper dive or has intimate knowledge, one can find gaps of understanding and an even religiosity attached to certain ideas and theories. Isn’t this so often the basis of what we see here on NC? The normative narrative is used to create outcomes that benefit a few at the expense of the many? This certainly seems yet another narrative worth exploring vs accepting the current one unexamined.

    1. Yves Smith Post author

      While much of medicine has less than ideal scientific foundations, due to the ethical and practical limits to collecting data on and experimenting on humans, you skepticism amounts to nihilism and denialism.

  11. JonnyJames

    So much information here on NC, and widely varied topics as well, thanks for posting. I think Yves meant to spell “Anglosphere” – a term I will use in future.

  12. Lambert Strether

    Thank you, KLG, for this magisterial intervention.

    On Tom Jefferson, first author of the Cochrane “study”: As I show here, Jefferson also writes for that nest of vipers at the Brownstone Institute, as does Unlisted Author Carl Heneghan.

    Importantly, from the same post, Cochrane requires Unlisted Authors like Heneghan to be credited and to be free from conflicts. Neither has been done in this case. Unless Cochrane choose to correct these lacunae, they should withdraw the paper. Cochrane’s brand is rigorous standards. So why not in this case?

  13. RM

    There is a lot of evidence on the effectiveness of masking in other respiratory illnesses, such as influenza, which is largely in line with the conclusions of the Cochrane review: there’s an uncertain and at best low magnitude benefit to masking. Why should things be different for Covid, for which droplet spread contributes less to transmission?

    There are of course lots of negatives associated with masks, not least of which are the environmental implications of huge numbers of people regularly consuming and disposing of the toxic materials from which they’re made. Uncertain and low-magnitude benefits may not therefore meet the threshold to warrant blanket recommendations for use (as they do not for influenza).

    1. Cat Burglar

      That looks like a misreading of the Cochrane study to me.

      The study stated that the bias risk, variable measurement methods, and low adherence to interventions in the studies they examined “hampers drawing firm conclusions.” “An uncertain and at best low magnitude benefit to masking” sure looks like you’re concluding something that was specifically disclaimed by the authors.

      1. RM

        “hampers drawing firm conclusions” = uncertain. Statements elsewhere in the paper, such as “wearing a mask may make little to no difference” = at best low magnitude benefit. Statistically speaking, the certainty of the effect estimate and its magnitude are two separate and independent parameters.

  14. marku52

    Well, they are funded by Gates, who made a bundle selling vaccines…..t

    They also squashed Tess Lawrie’s meta analysis that showed that good old “horse paste” worked just fine.

    So no, now just corporate hacks

    1. flora

      At this point I’m just trying to discern the $cientists from the scientists, to discern the science from the $cience. / ;)

  15. SocalJimObjects

    I think I’ve read somewhere that knowing when to sell is better than knowing when to buy when it comes to stocks. Masks work, full stop, but I think there’s not been enough discussion on when you can take them off. If you work in a lab, presumably you are going to be disinfected afterwards and then you can take off your PPE. For me, since I live alone, the answer is also easy, when I go out I wear my mask, and when I get home, I take it off, and since my home is always well ventilated, I know I am good. For people with families or roommates though, when is it safe to not wear your mask? Can you trust the people around you? How about if one of them were to get careless one time? Since Zero Covid is no longer on the table, I think it’s important to have some guidelines on this, or maybe there’s one already that’s easy to follow for most people.

    I’ve had some conversations with “anti maskers” in Taiwan, and to my surprise, their argument is not that masks don’t work, but at work, etc they would often go out to lunch and dinner with colleagues, and guess what, the virus does not care about whether you are having a meal or not, hence “masks don’t work”.

  16. Mirko

    Before discussing whether masks protect, we should assume where the fours penetrate. The eye mucosa should also be protected from a viral load. The nonsense “only a mask protects” was pointless for me (specialist ITS/IMC).

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