Clinical trials Medicine Science

About that Danish mask study that “shows that masks don’t work”…

Danish researchers published a negative randomized controlled study of masks to prevent COVID-19. Is this slam dunk evidence that masks don’t work? Not so fast, there pardner…

I not infrequently use the term “methodolatry” to refer to the seeming belief on the part of certain dogmatic evidence-based medicine (EBM) advocates who are so in love with the “pyramid of evidence” image frequently used in EBM to rank the strength of clinical evidence that double-blinded placebo-controlled clinical trials are the be-all and end-all of clinical research. Obviously, I didn’t coin the term, but rather learned it from a certain epidemiologist by the ‘nym of revere who used to be a fellow ScienceBlogger back in the day and defined “methodolatry” as “profane worship of the randomized clinical trial as the only valid method of investigation.” Ironically, the first time I encountered the term, way, way back in the day (11 years ago now!) was in the context of a risibly bad article in The Atlantic about Tom Jefferson and his work with the Cochrane Collaboration on the effectiveness of the influenza vaccine during the H1N1 pandemic. (Remember that pandemic from 2009-2010? We thought that one was pretty bad, but it seems quaint next to this year’s COVID-19 pandemic and its massive—and growing—death toll.) The reason revere (and I) accused Tom Jefferson of methodolatry back then was in part because of his annoying tendency to equate lack of statistical significance as the affirmation of the null hypothesis, which can be a serious interpretive error. He also basically failed to put randomized controlled trials (RCTs) into proper context with the totality of evidence. In any event, the reason I mention methodolatry and Jefferson again is due to an article and study that I came across co-authored by—you guessed it!—Tom Jefferson on masks and slowing the transmission of COVID-19. You probably also guessed that he referenced a recently published negative randomized controlled trial (RCT) of mask wearing to prevent COVID-19 as the be-all and end-all of evidence because it didn’t achieve statistical significance.

In the age of COVID-19, it seems, everything old is new again, including methodolatry.

Before I discuss the article, Landmark Danish study shows face masks have no significant effect, by Carl Heneghan and Tom Jefferson, and the Danish study on which it is based, let me just preempt one criticism that cranks are likely to throw back at me. I fully expect that they’ll accuse me of methodolatry in extreme skepticism early on that hydroxychloroquine is an effective treatment for COVID-19. My doubt was first based on the lack of, yes, RCTs and the reliance of hydroxychloroquine advocates on anecdotal and poor quality observational evidence. In fact, my doubt was justified and ultimately validated when RCT after RCT failed to find a therapeutic or preventative effect of hydroxychloroquine on COVID-19. The point is this: RCTs are indeed considered the “gold standard” for determining whether a specific treatment intervention works, but when it comes to complex public health interventions, such trials might well be impossible to do in such a way as to give a good answer. Similarly, in some cases, RCTs are unethical. For example, the classic “vaxxed/unvaxxed” RCT to determine if vaccines cause autism or whether unvaccinated children are “healthier” that antivaxxers frequently advocate would be utterly unethical because it would be unethical to randomize children to the unvaccinated (or saline placebo) control group, because that would leave the control group unprotected against potentially deadly vaccine-preventable diseases. To study such questions, we have to rely on epidemiology.

But back to Heneghan and Jefferson:

Do face masks work? Earlier this year, the UK government decided that masks could play a significant role in stopping Covid-19 and made masks mandatory in a number of public places. But are these policies backed by the scientific evidence?

Yesterday marked the publication of a long-delayed trial in Denmark which hopes to answer that very question. The ‘Danmask-19 trial’ was conducted in the spring with over 3,000 participants, when the public were not being told to wear masks but other public health measures were in place. Unlike other studies looking at masks, the Danmask study was a randomised controlled trial – making it the highest quality scientific evidence.

Around half of those in the trial received 50 disposable surgical face masks, which they were told to change after eight hours of use. After one month, the trial participants were tested using both PCR, antibody and lateral flow tests and compared with the trial participants who did not wear a mask.

In the end, there was no statistically significant difference between those who wore masks and those who did not when it came to being infected by Covid-19. 1.8 per cent of those wearing masks caught Covid, compared to 2.1 per cent of the control group. As a result, it seems that any effect masks have on preventing the spread of the disease in the community is small.

They even conclude:

And now that we have properly rigorous scientific research we can rely on, the evidence shows that wearing masks in the community does not significantly reduce the rates of infection.

This is not what the trial showed, or even what the authors of the trial were trying to show. Before coming back to Heneghan and Jefferson’s polemics, let’s take a look at the actual Danish study, published on Wednesday in the Annals of Internal Medicine, shall we? The publication, from a number of researchers at various Danish hospitals, reports the results of the DANMASK-19 trial (Danish Study to Assess Face Masks for the Protection Against COVID-19 Infection, NCT04337541).

The hypothesis to be tested was that wearing surgical masks outside of the home reduces the wearers’ risk for contrating COVID-19 “in a setting where masks were uncommon and not among recommended public health measures.” That last part is important, as this study was carried out early in the pandemic (April and May), before mask mandates became widespread. (More on that later.) In any event, let’s look at the trial’s endpoints:

The primary outcome was SARS-CoV-2 infection, defined as a positive result on an oropharyngeal/nasal swab test for SARS-CoV-2, development of a positive SARS-CoV-2 antibody test result (IgM or IgG) during the study period, or a hospital-based diagnosis of SARS-CoV-2 infection or COVID-19. Secondary end points included PCR evidence of infection with other respiratory viruses (Supplement Table 2).

These are not unreasonable endpoints for such a study, nor was the definition of COVID-19 infection unreasonable given what was known at the time. Before I get more into the weeds, let’s look at what the study found:

A total of 3030 participants were randomly assigned to the recommendation to wear masks, and 2994 were assigned to control; 4862 completed the study. Infection with SARS-CoV-2 occurred in 42 participants recommended masks (1.8%) and 53 control participants (2.1%). The between-group difference was −0.3 percentage point (95% CI, −1.2 to 0.4 percentage point; P = 0.38) (odds ratio, 0.82 [CI, 0.54 to 1.23]; P = 0.33). Multiple imputation accounting for loss to follow-up yielded similar results. Although the difference observed was not statistically significant, the 95% CIs are compatible with a 46% reduction to a 23% increase in infection.

Oh, no! An 1.8% infection rate in those wearing masks versus 2.1% in those not wearing masks, and it wasn’t even statistically significant! This must mean that masks don’t work! Damn Jefferson and his methodolatry, which might in this case be correct. Not quite, and not so fast, there, pardner:

Underpowered, Dr. Topol says? Let’s go to the tape and look at the power calculations:

The sample size was determined to provide adequate power for assessment of the combined composite primary outcome in the intention-to-treat analysis. Authorities estimated an incidence of SARS-CoV-2 infection of at least 2% during the study period. Assuming that wearing a face mask halves risk for infection, we estimated that a sample of 4636 participants would provide the trial with 80% power at a significance level of 5% (2-sided α level). Anticipating 20% loss to follow-up in this community-based study, we aimed to assign at least 6000 participants.

So the trial was designed and powered to look for a 50% decrease in risk for infection for the wearers, with an 80% power to detect such a decrease in risk if it were observed. Now, you might wonder why the authors didn’t look at mortality from COVID-19. The reason, I surmise, is that detecting a decline in deaths due to COVID-19 would have taken a much larger sample size, given that, even in the heat of the early part of the pandemic, infection fatality rates were in the low single digit percentages. In any event, a 50% decrease in risk to the wearer (the study didn’t even look at whether masks decreased the risk of transmission to others) would have been “quite a lot“! Of course, looking for less than 50% decrease in risk would have resulted in the need for a lot more participants, depending on what level of decline (e.g., 25% or 10%) in risk associated with the mask wearing.

Also, the study participants were only followed for one month after enrollment, with antibody testing performed at the beginning and end of the one month:

Participants in the mask group were instructed to wear a mask when outside the home during the next month. They received 50 three-layer, disposable, surgical face masks with ear loops (TYPE II EN 14683 [Abena]; filtration rate, 98%; made in China). Participants in both groups received materials and instructions for antibody testing on receipt and at 1 month. They also received materials and instructions for collecting an oropharyngeal/nasal swab sample for polymerase chain reaction (PCR) testing at 1 month and whenever symptoms compatible with COVID-19 occurred during follow-up. If symptomatic, participants were strongly encouraged to seek medical care. They registered symptoms and results of the antibody test in the online REDCap system. Participants returned the test material by prepaid express courier.

Written instructions and instructional videos guided antibody testing, oropharyngeal/nasal swabbing, and proper use of masks (Part 8 of the Supplement), and a help line was available to participants. In accordance with WHO recommendations for health care settings at that time, participants were instructed to change the mask if outside the home for more than 8 hours. At baseline and in weekly follow-up e-mails, participants in both groups were encouraged to follow current COVID-19 recommendations from the Danish authorities.

Why is this important? This is why:

Basically, one month is a very short period of time if the development of antibodies to SARS-CoV-2 was the most common method by which COVID-19 was diagnosed in the study population, and it was. 84% (80 of 95) diagnoses were made through antibody testing.

Trish Greenhalgh notes:

She also points out:

As an accompanying editorial by Thomas Frieden and Shama Cash-Goldwasser noted:

Perhaps the most important limitation of this study was the use of antibody tests to diagnose COVID-19. Of COVID-19 diagnoses in this study, 84% (80 of 95) were made by antibody testing. The accuracy of anti–SARS-CoV-2 antibody tests varies widely (7). Although an internal validation study of the assay used in DANMASK-19 estimated a specificity of 99.5%, the manufacturer reported ( a specificity of 97.5% (CI, 91.3% to 99.3). If test specificity was 98.5% and the 1.5% (1 − specificity) chance of a false-positive result was due to random laboratory variation, Bayes’ law implies that all of the antibody-positive results in both intervention and control groups could have been false positives. False positivity due to cross-reactive antibodies would have resulted in baseline exclusion, so the actual rate of false positives in participants after 1 month may be low. Nevertheless, given the very low (at most 2%) prevalence of infection, many of the follow-up positives may have been falsely positive and would be randomly distributed between intervention and control groups. This would bias the study’s findings toward the null.

To put it more simply, in a situation in which the disease being tested for is present at low prevalence (in this case, less than 2% of the population), even a test that is pretty specific and sensitive can produce a lot of false positives. I won’t go into the gory details (if you want discussions of sensitivity, specificity, and positive and negative predictive values, go here, here, and here), but what we are interested in in this case is the positive predictive value (PPV), which is the likelihood, given a positive test, that there really is disease present. The PPV depends on the prevalence of the disease in the population being tested. To put it simply (but hopefully not simplistically), the lower the prevalence of a disease, the lower the positive predictive value of a test for that disease, even a good one, is likely to be, because even low rates of false positivity will be high (half, equal, or even greater) compared to the actual prevalance of the disease in the population. The authors of the paper did not even try to correct their estimates for the sensitivity and specificity of the tests use.

Another issue is that this study was not even blinded, much less double-blinded. Of course, it would be difficult to design a double-blinded trial of mask wearing, although one might imagine the use of “placebo” mask that filter very little for the control group. Moreover, it’s true that not every intervention can be subjected to a blinded comparison to a “placebo” intervention, but RCTs can still be done and still be useful. Even so, this lack of blinding concerns me. Given that the study relied on email followup surveys to “collect information on antibody test results, adherence to recommendations on time spent outside the home among others, development of symptoms, COVID-19 diagnosis based on PCR testing done in public hospitals, and known COVID-19 exposures,” it’s easy to see that recall bias could also be a major factor in whatever results were obtained. Similarly, there could be all sorts of other confounders associated with wearing a mask, none of which were really examined, although adherence to mask wearing was. Guess what? The results weren’t great:

Based on the lowest adherence reported in the mask group during follow-up, 46% of participants wore the mask as recommended, 47% predominantly as recommended, and 7% not as recommended.

So less than half of the masked group actually wore their masks as recommended, most of the other half either didn’t wear them correctly or only “predominantly as recommended.” When you have a study that is already underpowered, it doesn’t help if less than half of your experimental group actually does the preventive intervention correctly all the time, that just makes it far more likely that you will fail to find a statistically significant result.

The bottom line is that this study does not show that masks don’t work to slow the spread of SARS-CoV-2! Even the authors hasten to point this out in the discussion:

In this community-based, randomized controlled trial conducted in a setting where mask wearing was uncommon and was not among other recommended public health measures related to COVID-19, a recommendation to wear a surgical mask when outside the home among others did not reduce, at conventional levels of statistical significance, incident SARS-CoV-2 infection compared with no mask recommendation. We designed the study to detect a reduction in infection rate from 2% to 1%. Although no statistically significant difference in SARS-CoV-2 incidence was observed, the 95% CIs are compatible with a possible 46% reduction to 23% increase in infection among mask wearers. These findings do offer evidence about the degree of protection mask wearers can anticipate in a setting where others are not wearing masks and where other public health measures, including social distancing, are in effect. The findings, however, should not be used to conclude that a recommendation for everyone to wear masks in the community would not be effective in reducing SARS-CoV-2 infections, because the trial did not test the role of masks in source control of SARS-CoV-2 infection. During the study period, authorities did not recommend face mask use outside hospital settings and mask use was rare in community settings (22). This means that study participants’ exposure was overwhelmingly to persons not wearing masks.


The most important limitation is that the findings are inconclusive, with CIs compatible with a 46% decrease to a 23% increase in infection. Other limitations include the following. Participants may have been more cautious and focused on hygiene than the general population; however, the observed infection rate was similar to findings of other studies in Denmark (26, 30). Loss to follow-up was 19%, but results of multiple imputation accounting for missing data were similar to the main results. In addition, we relied on patient-reported findings on home antibody tests, and blinding to the intervention was not possible. Finally, a randomized controlled trial provides high-level evidence for treatment effects but can be prone to reduced external validity.

Our results suggest that the recommendation to wear a surgical mask when outside the home among others did not reduce, at conventional levels of statistical significance, the incidence of SARS-CoV-2 infection in mask wearers in a setting where social distancing and other public health measures were in effect, mask recommendations were not among those measures, and community use of masks was uncommon. Yet, the findings were inconclusive and cannot definitively exclude a 46% reduction to a 23% increase in infection of mask wearers in such a setting. It is important to emphasize that this trial did not address the effects of masks as source control or as protection in settings where social distancing and other public health measures are not in effect.

Or, as our old friend points out:

Precisely, which brings me back to Heneghan and Jefferson. Given that they are both EBM aficionados, you’d think that they wouldn’t have referred to this study as the “highest level of evidence,” given its many shortcomings. Let’s just put it this way. There are times when a well-designed, adequately powered epidemiological study is more valuable than an underpowered RCT with a lot of holes in its design (if you’ll excuse my using the word “holes” in the context of debates about masks), particularly when it comes to an issue as complex as preventing the spread of COVID-19, which is a multifactorial process in which multiple interventions will interact with each other and also depend on the prevalence and rate of spread of the virus, as Christine Laine, Steven Goodman, Eliseo Guallar note in another accompanying editorial:

Two aspects are important to note. First, the study examined the effect of recommending mask use, not the effect of actually wearing them. Adherence to public health recommendations is always imperfect, as it was in this study, and can differ dramatically in communities with different attitudes toward such recommendations. Second, the effect of a mask recommendation also depends on many other factors, including the prevalence of the virus, social distancing behaviors, and the frequency and characteristics of gatherings. Mask wearing is just one of several interacting strategies to reduce viral transmission, with each reinforcing the others.

They somewhat drolly note that mask wearing “by a minority of persons—even with high-quality surgical masks like the ones provided to trial participants—does not make the wearers invulnerable to infection.” Masks can, however, decrease one’s risk of infection and act as source control to decrease the risk of infection of others by persons currently infected with COVID-19.

As Frieden and Cash-Goldwasser note:

Community mask use can substantially reduce risk for SARS-CoV-2 transmission, especially when enough people use them and when mask use is combined with other effective public health and social measures. Multiple observational studies have documented an association between mask mandates and reduced COVID-19 incidence (9). Although randomized controlled trials are often presumed to provide the highest-quality data, observational studies may in some settings be more accurate and can overcome some limitations of other data sources (10).

The CDC recently summarized the evidence that community use of cloth masks is an effective means to control the spread of COVID-19 recently, and the evidence is compelling, which is why it is disheartening to see Tom Jefferson engaging in methodalatry again, and, embarrassingly for him, doing it rather badly, given how he’s misrepresenting what this study actually finds, as well as its actual usefulness in determining if mask mandates are good public health policy.

Finally, prepare yourself for the antimask cranks using this study to “prove” that masks don’t work and are fascism/socialism/communism/deep state conspiracy (pick one or more). It’s already happening.

By Orac

Orac is the nom de blog of a humble surgeon/scientist who has an ego just big enough to delude himself that someone, somewhere might actually give a rodent's posterior about his copious verbal meanderings, but just barely small enough to admit to himself that few probably will. That surgeon is otherwise known as David Gorski.

That this particular surgeon has chosen his nom de blog based on a rather cranky and arrogant computer shaped like a clear box of blinking lights that he originally encountered when he became a fan of a 35 year old British SF television show whose special effects were renowned for their BBC/Doctor Who-style low budget look, but whose stories nonetheless resulted in some of the best, most innovative science fiction ever televised, should tell you nearly all that you need to know about Orac. (That, and the length of the preceding sentence.)

DISCLAIMER:: The various written meanderings here are the opinions of Orac and Orac alone, written on his own time. They should never be construed as representing the opinions of any other person or entity, especially Orac's cancer center, department of surgery, medical school, or university. Also note that Orac is nonpartisan; he is more than willing to criticize the statements of anyone, regardless of of political leanings, if that anyone advocates pseudoscience or quackery. Finally, medical commentary is not to be construed in any way as medical advice.

To contact Orac: [email protected]

71 replies on “About that Danish mask study that “shows that masks don’t work”…”

Jefferson has recently been one of the expert witnesses in a lawsuit by the antivaccine organization the Children’s Health Defense against the university of California’s influenza vaccine mandate. The judge has denied them a preliminary injunction because their chances of success were low and the balance of harms favors the university.

So serving the interests of opponents of public health is becoming a constant.

In this case, he should know this is not a good counter to mask use against COVID-19.

Obviously, grifters have got to grift. I have seen Jefferson moving steadily in the direction of the anti-vax movement over the years and at first was reluctant to believe it. I initially passed it off as him quibbling about data on individual vaccines. Now there is no doubt, he has gone full bung anti-vaccine.

I often wonder what triggers scientists to leave their training behind for conspiracy theories. I think it boils down to on overly inflated sense of their own importance and not getting the recognition they desire from their colleagues. On the other hand, conspiracy theorists are happy to lay out as much adulation out there as required.

I think that you’re correct; also, conspiracy-based explanations are so much easier than doing the real work digging through data and evaluating results. Right here, we see how Orac painstakingly goes over a study and then cautiously provides a summary, yet internet radio woo-meisters or RI trolls just yap, “It’s all RONG!”
Barrett, in an article written long ago, ventured that it was especially medical personnel who had little power ( e.g. such as in a hospital setting) that were most likely to seek ways to ‘fight the power’ of authority and consensus and become rebels.

re masks;
there’s a new myth ( courtesy of PRN) that masks protect you from other stuff but NOT Covid which hasn’t been elucidated as yet but I imagine I will learn how soon. But if this is true- and the prevaricator in charge is so well informed about medicine ( yeah, right)’ why didn’t he mention this prior to 2020?

Woo-meisters and anti-vaxxers on the het/ social media need attention grabbers to keep and expand their audiences and Covid is big news. If Dr Fauci** or another well known expert says anything you can be sure the usual suspects will negate it almost immediately,

** despite the fact that he is on television so frequently, a well known woo-meister can’t pronounce his name correctly. .

To the authors’ credit, they did a Q&A on Danish national news pretty much immediately where they proceeded to tell people to WEAR A FUCKING MASK, and underlined time and time again that their results didn’t show masks were useless. They got their share of cranks asking about “side effects” or “damage” caused by masks, but they shot that down quickly.

That’s good. However, it does rather irk me that the authors did a study that they knew to be underpowered even if adherence to masking instructions was near-perfect (which it wasn’t, obviously). They should have known when they started that the most likely result, even if masks worked, was a failure to find a statistically significant difference in the primary endpoint between control and intervention groups.

Though one of them has since gone on to say that “it’s possible to question the quality of the evidence there is, but as long as it’s the generally accepted perception that masks likely protect, we can’t argue for doing a new study”. I’m not sure how much of it is him saying it’s a problem it can’t be redone, and how much of it is the news article he’s cited in doing so, but… yeah. (They do mention that it’d be unethical to redo the study, and cite someone else who sounds more along the lines of “sometimes you have to be content with the knowledge you have”.)

A study set up with the best of intentions, but hopelessly flawed from the start. I really don’t know what else to say.

Even the question they were asking was the wrong one. We know that masks won’t protect you from SARS-CoV-2, unless they are the correct type of mask and are warn properly all the time you can potentially be exposed. If you mask everybody, then you do start providing protection, because there are much fewer droplets in the air containing viral particles.

To answer the question of whether surgical masks provided some protection as worn by the populace (which they probably do in that it is better than having no mask), you are probably going to want to be able to find something like a 20 or 25% reduction in infection and so needed a much bigger study than this one.

We know that masks won’t protect you from SARS-CoV-2

More accurately: the mask you are wearing won’t protect you (much) from the virus.
But it will (mostly) prevent you from infecting others.

I got it wrong myself about mask usefulness early on, but I managed to get it corrected in my bird-sized brain (thanks to people here and on another blog patiently repeating the hard facts).
I sit back hard when I realized the mix-up in the interpretation of this study. Like, oh no, not again?

I get it that they wanted to measure the “(much)” part in the “won’t protect you (much)”, it’s not a stupid question.
It’s just… How did they manage to get their starting assumptions of usefulness so wrong?

Not to mention the timeframe. Were they planning on the low prevalence at that time to get plenty of subjects with a high chance of being uninfected at the time of enrolling? The virus is not here yet, so no need to worry about people having been infected one week before?

Thx, Orac. Also that idea of ‘variolation’ with mask wearing. Perhaps that would also lead to a positive antibody test. I’ve read somewhere (maybe here, maybe the other one, maybe ARS) that possibly up to 80% of infections are asymptomatic in areas with high mask participation. I take it that the study did not compare between severity of infection.

Somebody had to go and make it tribal; Just look at those Dakotas:

I recently saw a map of Covid infections that eerily resembled the final election map: both showed lots in red in the middle.
But good news:
yesterday, a few governors in the north central region advocated for masks with the glaring exception of the woman from SD (IIRC)

If people wore masks and followed other simple methods ( distancing, less indoors, avoid crowds) perhaps we can avoid another shutdown ( Fauci)

I saw the SD governor on CNN a few hours ago (she is easy on the eyes but so ‘freedom oriented’ with only now the possible cannabis is kinda a deal breaker for me) and they don’t even have the six feet. They are just letting it rip. I don’t know anything about the state — could be 150 people live there and they are all swapping it around at the only Dollar General — but, apparently, the positivity rate is –>60%

I wonder if they are only testing people with symptoms but I don’t see this going well in any scenario, especially when adjoing hospital districts have their own to worry about.

I get that they have short warm and sunny days, but so do other states doing much better. What could it be for positivity but masks? If deaths/cases are way higher, then I might look to vitamin D status. And health infrastructure.

South Dakota can best be described as a basket case. They have a population that is half the state I live in, yet we have 550 cases and 4 deaths. We are also on the last day of a complete lockdown (cannot leave home, one person from each household can leave once a day to the supermarket for essential supplies).

The fact that public health has become so partisan is actively killing people.

“Hey, Mac; What’s in the basket?”

“cannot leave home”

This, I’m absolutely against. Plus, it goes counter to guidelines that recommend more time outdoors. I look at it like being in a garage with car exhaust or outside with the same emissions. Especially when one is on his own under the bridge down by the river or on a nice back 40 trail.

Myself, I only leave home once a day for essential alcohol and to caretake for my (I advised against him going) away employer; but still.

We can expect that the anti-vaccine, anti-mask extremists will be spouting off about this study. The state legislature in Ohio just passed the terrible bill, SB 311, that reduces the ability of the health department to institute public health measures to control spread of this virus. The PAC for the Ohio State Medical Association gave money to a bunch of anti-vaccine, anti-mask politicians like Diane Grendell and Jerry Cirino, both backed by the anti-vaccine group OAMF. They need to be called out.

The PAC for the Ohio State Medical Association gave money to a bunch of anti-vaccine, anti-mask politicians

I am Canadian so I must be missing something. Why would a bunch of doctors be trying to kill their patients?

Libertarianism? It seems to have completely infected the US. The Government should not be allowed to tell people what they can and cannot do.

When I looked through the study, there seemed to be one other gap. Did they look at all for mask-wearing in the control group? Just because they were not told to wear masks in an interview, and not given masks, doesn’t mean they did not wear them.

Anecdata-wise, it seems fairly unlikely that they would – around that time there was a LOT of griping about mask-wearing here in Denmark, and I’m pretty sure I could count the amount of people I saw wearing a mask when I went grocery shopping in the months before the health authorities friggin’ finally recommended them on one hand. (The broad sentiment did feel a little “we’ve never had to wear masks, so we clearly know better” to me… thankfully people now at least try to wear them, even if you can still play Mask Fail Bingo when you go out.)

Another thing in the study that may well have affected the results in the ‘self-administered swabs’, I haven’t had a test, but I understand that getting the swab far enough up your nose to be swabbing where it’s actually going to collect enough virus (assuming it is present) is distinctly uncomfortable. Will the trial participants have done this? I don’t know, and without at least a sub-set of participants also tested by trained personel taking taking swabs the authors don’t know either. This is likely to affect both wings of the trial equally, and so not affect the resuls of the study, but again without confirmatory testing we don’t know that.

I listened to a podcast on BBC (Inside Science) that discussed in detail how Covid-19 tests results were affected depending on how experienced the medical personnel were at performing them–it was significant! So I can only imagine the room for error with self-administration.

A friend of mine is participating in a local SARS-CoV-2 surveillance study where she’s asked to do a nose-swab test every month or so. But it’s just the antigen test, so the swabbing is in the front end of the nose and not all the way up at your skull.
Much easier for the lay person to do to themselves.
Maybe that’s the kind of test they were using for this study?

a recent CVC study found conclusive results that transmission of COVID-19 occurs mostly through news broadcasting. The virus settles in between the ears and affects rational thinking. Symptoms may include hyper-vigilant cleansing, distrust of friends and neighbors, and an overwhelming urge to give up basic human rights for the perception of safety. Individuals with larger vacuums between the ears are at higher risk.if you do feel the need to cosplay for a virus with a literal 0.26% mortality rate once asymptomatic numbers are factored in, then giddyup cowgirl but don’t be a masknazi it only exposes you for your fearmongering and susceptibility to communist ideologies

“I don’t care what an anonymous troll thinks.”

Who probably does not even know how to hold a guitar. Though it is amusing he used the unusual name of a performer who died in his early 50s due to substance abuse.

This virus does not care about your snowflake feelings or your supposed “freedom.” Those who caught it and were on ventilators and now cannot walk any distance don’t seem to be “free” anymore. Especially those who lost their health insurance because they cannot work.

It is pure idiocy that thinks “death” is the only bad outcome. Thanks for blowing in here to show us your proud and out loud depths of ignorance.

Using the numbers from

261,746 deaths / 12,435,885 cases * 100 = 2.1%

So you are also very bad at basic math. You probably also do not understand why a study like this that only went for a months is also very mathematically unrealistic.

First of all, anti-mask and anti-vax need not have a thing in common; I’m happy to receive any vaccine available to me and am grateful to able to have my children vaccinated. When I’m a foot away from a surgically exposed patient, I find it a good idea to wear a surgical mask. When I’m walking around inhaling and exhaling the outside air, I do not. It’s funny… you incorporate bits of sound reasoning throughout but somehow are still too much of a moron to assimilate those points into the correct conclusion. But by all means
though, carry on spreading fear and promoting government control you fucking prick

It is not so much “Voice of Reason” but special snowflake who does not care about public health. One foot is not enough, fool.

That’s not what communist, or even Communist, means.

“Give up basic human rights”? What rights? The right to not wear a mask? Where is that right enshrined?

If you feel that being asked to wear a mask is giving “up basic human rights” then you don’t fly commercial aviation, do you? You know, where you have to show ID and go through a metal detector and have all your liquids in a quart-sized zip-top bag? How is that less intrusive than wearing a mask?

CP: “I often wonder what triggers scientists to leave their training behind for conspiracy theories. I think it boils down to on overly inflated sense of their own importance and not getting the recognition they desire from their colleagues.”

A good description of Judy Mikovits, heroine of “Plandemic” and opponent of masks.

The same thing that creates every conspiracy theorist out there. Something that they don’t understand and can’t accept.

First of all, anti-mask and anti-vax need not have anything in common; I’m happy to receive any vaccine available to me and I’m grateful to have my children vaccinated. When I’m a foot away from a surgically exposed patient, I find it to be a good idea to wear a surgical mask, and when I’m walking around inhaling and exhaling the outside air, I do not. It’s funny… you were about to incorporate various pearls of the way the literature should be analyzed but are still too small minded… or more likely too prideful… to arrive at the proper conclusion. Who knows what you were like in med school… wouldn’t even surprise me if you were near the top of your class… because I see “smart” doctors all the time that for whatever reason aren’t quite able to ever convert their aquired knowledge into something that actually benefits patients

” When I’m a foot away from a surgically exposed patient,”

Which proves you are a sock puppet idiot. VoR and Not a DoctorR… “surgically exposed patient” makes no sense.

I didn’t see any discussion of/control for dining/drinking out. Unless the study subjects are uniquely talented, they would presumably be unmasked to eat or drink. Since much of the transmission occurs indoors in restaurants and bars, that missing control variable would obviously bias toward the null. As its flaws pile up, the study does serve one purpose: if one is looking for a textbook case of how not to design an authoritative study, there is little need to look beyond this one.

Well, to be fair, this started when a lot was locked down, so IIRC during at least most of the period subjects couldn’t dine out because everything was closed here… yep, as per the study itself: “Cafés and restaurants were closed during the study until 18 May 2020”. Though that does leave May 19th-June 2nd – I don’t quite remember what the regulations were then because I personally stayed the hell away from everything.

I take it that your ‘origin server’ is down because rioters busted in and smashed your laptop. And the covefe maker it was sitting next to. I know it is getting ugly down here.. Frankly, I’ve gotten too old for this shit.

This belatedly reminds me, our old friend Peter Gøtzsche’s gone antimasker. And I think when the study hadn’t been published yet he claimed it was because the results would be “politically incorrect” (not sure if he believes that any medical journal cared one whit about Danish health policy, or if he believes there’s a global mask conspiracy). The article’s here: ; but it’s in Danish and paywalled, and while I could help with the former, I am not paying anything to read that.
I can tell you that the title is “stop the corona-hysteria and drop the masks”, and the sentences that you can read without paying are something to the effect of “It’s unacceptable that researchers behind a study about the effect of masks haven’t already shared their results with others, all while the whole world is ordered to wear masks. Now we can’t survive any longer without resembling bank robbers when we go grocery shopping. In the span of a few years, we’ve gone from forbidding masks to an order to wear masks to reduce the risk of being infected with coronavirus, but this likely doesn’t work. (inserted quote: “There’s just 700 people who have died with corona. Every year 14 000 die of smoking.”) A large Danish study where half of 6000 people wore masks and the other half didn’t has been rejected by three top journals. The researchers behind the study have called it unique and the results controversial, and have said that it will be published…”
And that’s where I hit the paywall. His claims re: “political correctness” probably happen further down, I only know these secondhand from Twitter.

there’s a global mask conspiracy

Of course there is! It is a nefarious plan by the Bildebergers, Bill Gates, the Illumati and George Soros though some people maintain that Vladimir Putin and Maurice Strong are part of it.

Why? Well, because! It’s obvious.

@ Sue Deauxnim:

Over the past few years, I have been able to accurately predict when people who seem to be science/ reality based are about to go woo; Gotzsche, Jefferson, that guy at BMJ, Peter Doshi and Herbert- Is it?- from Harvard:
no, it doesn’t prove that precognition exists because I listen to Gary Null’s daily show ( see and they appeared as guests spouting contrarian viewpoints early on in their alternate careers**. Because the charlatan-in-charge presents the site as a legitimate news source, most of these shows are archived and easy to find through google or bing.

** it also illustrates that they are not very good at researching outlets:. .
I once e-mailed a former US cabinet member/ advisor ( although he didn’t go rogue on his basic ideas) informing him about what type of media he enabled and how the host frequently misrepresented, insulted and lied about his views, his close associates and political party ( I’m deliberately being vague in order to not identify him because other than this faux pas, he is quite admirable and very respected in his work )
fortunately, he never appeared again and no longer allowed his articles to be featured at the prn website…

Thanks for the interesting post, Orac. It’s time to unmask the pet issue.

Q. Should dog parks be closed and pets locked down during a pandemic.

The CDC writes,

“A small number of pet cats and dogs have been reported to be infected with SARS-CoV-2 in several countries, including the United States.”

@ Denise Walter,

Would you let your pet(s) roam freely knowing they could be a vector for spreading the virus to other animal, and possibly humans, through social interaction? Please advise

@ MJD:

Actually a reasonable question.

First of all, I wouldn’t let ANY pet roam freely because it’s dangerous in general – cars, parasites, other animals, cruelty- not Covid related.
There’s an article about Covid and dog parks ( U Wisconsin-Madison News, 3 Sept 2020) that warns how dog parks can spread Covid amongst humans so the usual precautions stand. With millions of cases worldwide, only a few pets have contracted it which seems most likely from human-to-pet, not the reverse or amongst pets

I now only assist outdoor semi-feral cats that live under buildings and are beyond my control, having minds of their own: cars, parasites and other viruses are probably the major worries, not Covid.

that warns how dog parks can spread Covid amongst humans

Eh; I saw recently in the news how people walking their dog are more at risk of catching Covid19 than other people, all other things being equal.
I was thinking, maybe it’s meeting other dog owners in the street, but I forget about the existence of dog parks. A place where people would converge and cluster. Or just share the same space, even if it’s at different times of the day.
The penny dropped.

To answer/comment on MJD first point, I believe it has been shown already that our pets may catch the Covid19 virus, but don’t seem either to get sick from it or pass it back. So they shouldn’t be any trouble.
Uh, if you have mustelid pets, that could be a different issue. I’ll defer to any veterinarian in the room to answer this one.

[…] anti-mask loons have been citing as evidence that masks don’t work against COVID-19, but they’re completely – and deliberately – misinterpreting that study’s methods and con…. Among other things, the study didn’t even look at whether wearing a mask prevented […]

Nope, antimask & antivax are not the same thing. I am antivax & I am happy to mask. Started masking for covid in January & will continue to do so; not just until a vaccine but especially after the vaccine. Masks work.

Also, the tests are crap. Too many false negatives; they are not catching the full impact of this virus.

Now while we are in the mood for debunking studies (or their message); please tackle this one:

It’s truly awful & if you can’t see it, you may be biased.

Perhaps you should do debunking yourself. Paper is about right coronavirus. at least.
A paper about COVID tests:
Bisoffi, Z.; Pomari, E.; Deiana, M.; Piubelli, C.; Ronzoni, N.; Beltrame, A.; Bertoli, G.; Riccardi, N.; Perandin, F.; Formenti, F.; Gobbi, F.; Buonfrate, D.; Silva, R. Sensitivity, Specificity and Predictive Values of Molecular and Serological Tests for COVID-19: A Longitudinal Study in Emergency Room. Diagnostics 2020, 10, 669.
“The molecular test RQ-SARS-nCoV-2 showed the highest performance with 91.8% sensitivity, 100% specificity, 100.0% PPV and 97.4% NPV respectively”
Crap is not the right word.

@ Aarno

Paper is about right coronavirus. at least.

I’ll admit, it’s something to be highlighted. Here and in Orac’s friends’ blogs, plenty of people showed up with articles on other viruses. Or other bugs.

@ CK

Masks work.

Yep. But mostly to protect people from being infected by the mask wearer. Standard masks don’t offer a big protection to the wearer against infected people around him/her.
It’s in essence that this Danish study confirmed. If we squint a bit at the results.
Better than nothing, though.

Also, the tests are crap. Too many false negatives; they are not catching the full impact of this virus.

This is a refreshing stance. Most complainers are about how the PCR tests are too sensitive, and how the virus spread and harm are exaggerated.

Which tests were you thinking about, specifically?

@ Aarno,

"Perhaps you should do debunking yourself."

I already did. If the Mumps titre is associated with decreased covid severity; they have not proven that the decreased severity is due to the MMR.

*”The first group was the MMR II group, which consisted of 50 subjects (33 women and 17 men; mean age, 30.6 years [standard deviation {SD}, 7.6 years]) whose only likely source of MMR antibodies would have been the MMR II vaccine.” *


“Of these, 40 had previously had COVID-19-positive test results, with statuses ranging from asymptomatic to requiring a ventilator, and 10 subjects were functionally immune (COVID-19 negative despite strong COVID-19 exposure). Functionally immune subjects had had several days of close contact with someone who was symptomatic and who had tested positive for COVID-19, without either person social distancing or wearing masks. Despite the extensive contact, the functionally immune subjects tested negative for COVID-19 and never exhibited symptoms”

So one-fifth of the “vaccinated” group tested negative for covid & never even had covid symptoms. In a study looking at severity.

“The remaining 30 subjects (18 women and 12 men; mean age, 57.4 years [SD, 7.8 years]) made up the members of the comparison group, all of whom tested positive for COVID-19 and had been born before 1 December 1976. All subjects in the comparison group had birth dates at least several years before the MMR II vaccine was launched, and none had any record of ever having received an MMR II vaccination or booster.

Sorry but the MMR was licensed in 1971, and 40 percent of American children had received the combined vaccine by 1974.

And the study is looking at severity & compared severity for mean age of 30 year olds to mean age of 57 year olds.

And ALL of the “unvaccinated” group tested positive for COVID-19. They did not include any “functionally immune” subjects in their unvaccinated group.

“Masks work.”

Well, they don’t protect against HIV, HPV, or hepatitis which are also all viruses. No, wait…

@ Athaic,

Right; most antivaxxers & antimaskers believe the tests are producing false positives but this could not be further from the truth. I think both the molecular test for active infection AND the antibody tests are missing the mark.

I’m afraid covid is operating on a different pathway & the typical way of detecting viruses in general is inefficient for covid. Also, the presence of antibodies is not going to be relevant for resisting reinfection.

I get made fun of here a lot for relying on my hyperlexic sorting of written anecdotal experiences & the value I place in that but I am following the experiences of COVID Long Hauler’s closely & am noticing an alarming trend. Positive confirmations after multiple negative tests:

"My daughter had 3 rapid tests all negative. Severe Covid symptoms and then finally a 5-7 day test shows she is positive. She has had 2 positives within 15 days. She is not getting

"It was negative and was told it’s just allergies. A week later I was the sickest I’ve ever been in my life and tested negative, then positive 3 days later."

The antibody test in particular is problematic. Recovered covid patients are trying to donate plasma; they have to be tested for antibodies but the tests are not detecting them. Like these:

"I tested positive for the virus in April and negative for the antibodies in May."

"I donated plasma yesterday (August) and tested negative for antibodies- though highly symptomatic and positive PCR test on July 20"

"my Dr had several patients the week before that tested positive for Covid when they first got sick and then last week tested negative for antibodies".

"Had severe Covid pneumonia back at the beginning of July. Tested positive (4 different occasions) for 10 weeks. Finally negative 9/14. Antibody test 9/3 was positive (IgG & IgM).
Repeat antibody test in 10/1 was negative (IgG & IgM). My PCP wasn’t confident in those results. So now as of today, IgM is negative & IgG is positive.
Can someone help me understand this?"

"Covid...3 positive tests-March- may. June covid finally negative. 2 antibody test after that. Both negative"

I mean, if it was just some random person here & there that would be one thing but there are hundreds, if not thousands of these accounts. The viral spread & harm is not over exaggerated; it is under exaggerated.

“I get made fun of here a lot for relying on my hyperlexic sorting of written anecdotal experiences & the value I place in that”

Many, many times it’s been patiently pointed out to you that relying on a limited selection of unverifiable anecdotes that confirm your poorly reasoned personal prejudices is a colossally bad way to formulate opinions.

That’s not “hyperlexic” – it’s a profound deficiency in critical thinking skills. That can be overcome, but only if you want to.

Plus, hyperlexia is generally defined as the opposite of dyslexia — where word decoding skills are higher than actual reading comprehension. Bragging about your ability to read things you lack the skill to understand is… not very impressive.

@ DB,

No, the hyperlexia involves reading a huge amount of those written accounts in a very short time & stereotyping the information into an observable pattern.

@ DB,

And … I am not wrong about the tests. They are too prone to false negatives.

@Christine Kincaid As I said, there is this paper:
Bisoffi, Z.; Pomari, E.; Deiana, M.; Piubelli, C.; Ronzoni, N.; Beltrame, A.; Bertoli, G.; Riccardi, N.; Perandin, F.; Formenti, F.; Gobbi, F.; Buonfrate, D.; Silva, R. Sensitivity, Specificity and Predictive Values of Molecular and Serological Tests for COVID-19: A Longitudinal Study in Emergency Room. Diagnostics 2020, 10, 669.
You probably would be interested. But remember, not all tests are serological.

“molecular test for active infection” What test is that?
Molecular testing can’t determine if a virus is infective. Only cellular testing can do that.

Molecular testing looks for the presence of viral RNA. That’s it.

“They are too prone to false negatives.” Then why aren’t you making a better one?
That’s what a friend of mine has been doing. Why aren’t you making better tests rather than just complaining? Or at least determining a better testing regimen, layering different kinds of test on each other.

@ JustaTech,

I would love to be involved with something like that some day. But for now I am doing something much more important; being a mom.

The tests are crap & that matters. It will matter even more as our rates continue to climb, only this time; the case fatality rates will climb higher than ever before. But the fact that the tests are crap matters most for those left alive but still not recovered.

@ Terrie,

No, hyperlexia means precocious reading & there are several types. I am ASD hyperlexic, which is not the same thing as just reading early. Part of mine involved reading ability prior to the age of 2 & reading at HS grad level by the 2nd grade. Along with other peculiarities that I am not going to divulge here, at this time.

“Hyperlexia is characterised by strong decoding skills and delayed comprehension.”

Ostrolenk A, Forgeot d’arc B, Jelenic P, Samson F, Mottron L. Hyperlexia: Systematic review, neurocognitive modelling, and outcome. Neurosci Biobehav Rev. 2017;79:134-149. doi:10.1016/j.neubiorev.2017.04.029

“Comprehension of that which is masterfully read is often poor.”

Treffert, D. A. (2011). Hyperlexia III: separating ‘autistic-like’ behaviors from autistic disorder; assessing children who read early or speak late. Wisconsin Medical Journal, 110(6), 281-286.

Hyperlexia is early decoding, not early comprehension. It does not give you, an adult, any special insight into the content, any more than a choral singer’s ability to know the pronunciation rules for Latin means they have any idea what the words mean.

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