The Danish Mask Study has caused a furore, writes MedicalBrief. It has been seized upon by those militantly opposed to wearing masks as proof that medical recommendations to do so are rubbish. From the other side of the spectrum, some public health experts argue that the study should never have been published, since it gives ammunition to naysayers and undermines WHO and government advisories on COVID-19.
The idea that a study should not be published because the results are unsavoury to some, is an anathema to researchers (and journalists). But the saga also kicks up an emerging problem for medical science – as the volume of research burgeons but not always its quality, there is a growing number of similar studies with contradictory results. Which research to believe?
This becomes an important question, but the Danish study appears to be more of an example of good quality research that is misinterpreted and misrepresented, in cases to provide evidence supporting different ideological positions.
The DANMASK-19 trial – also important because it was the first of mask-wearing during COVID-19 – provided solid answers to the questions it asked.
There were some research limitations, but the main problem was the study’s limited parameters – it showed that wearing masks did not work very well where there were low infection rates and some social distancing.
The study reported that wearing “surgical masks to supplement other public health measures did not reduce the SARS-CoV-2 infection rate among wearers by more than 50% in a community with modest infection rates, some degree of social distancing, and uncommon general mask use. The data were compatible with lesser degrees of self-protection.”
The results would likely be very different in different circumstances, and indeed other subsequent studies have showed this to be the case. Ultimately, therefore, the problem is not the research but its misuse in and by society – and particularly social media.
Lead researcher behind Danish study says still wear a mask
In a Forbes article on 18 November, Leah Rosenbaum wrote that the study, published that day in the Annals of Internal Medicine, created a heated discourse on social media as some claimed that the study showed masks were ineffective at preventing COVID-19 transmission, while health experts – including the lead researcher behind the study – disagreed.
The research, by cardiologists in Denmark, studied about 6,000 participants, half of whom were told to wear masks and half of whom were not. “The authors found that 42 of the participants who were told to wear masks contracted COVID-19, while 53 of the participants in the control group got the disease, a difference they said was not statistically significant.”
The study did not investigate whether masks prevented those infected with COVID-19 from infecting other people, continued the Forbes article, adding:
“Some politically conservative voices on social media have touted this study as proof that masks won’t stop the spread of COVID-19.
“However, experts swiftly pointed out that the study has many limitations, including low compliance (many people did not complete the study, and a high percentage of people who were supposed to wear masks did not) and that it took place in a population where spread of COVID-19 was already low.
“Multiple studies have found that mask-wearing has a big impact on COVID-19, including one in October which found areas in Tennessee with mask mandates had lower hospitalisation rates than areas that don’t.”
The Forbes article argues that the Danish study should not be used as evidence to not wear a mask. “Even a small degree of protection is worth using the face masks,” says Dr Henning Bundgaard, professor of Cardiology at Rigshospitalet in Denmark and lead author of the study, “because you are protecting yourself against a potentially life-threatening disease."
Forbes mentions a response to the study written by Dr Tom Frieden, former director for the US Centers for Disease Control and Prevention (CDC), that was also published in Annals of Internal Medicine.
In it, Frieden “pointed out that among other limitations, the study authors used antibody tests to diagnose cases of COVID-19 which could have led to a significant number of false positives. In addition, the authors did not make an effort to ensure that people who were told to wear masks wore them correctly, or at all times.”
According to Forbes Dr Christine Laine, an internal medicine physician and Editor-in-Chief of Annals of Internal Medicine, said the study had done a good job of answering a specific question: whether or not face masks protect wearers from SARS-CoV-2 infection in areas with low infection rates and high levels of social distancing.
"It did not answer the question about whether widespread masking mitigates SARS-CoV-2 infection,” she says, adding that while there were concerns over misinterpretation, the editors agreed publishing the study was important because at that time it was the only randomised control trial of masks for SARS-CoV-2 infection that has been done”. Laine said: “This was an important, well-designed study.”
The full Forbes story can be accessed via the link at the bottom.
The curious case of the Danish mask study
Kamran Abbasi, executive editor, BMJ. Published on 26 November 2020
This is the British Medical Journal editorial on the topic:
“DANMASK-19, the first trial of mask use during COVID-19, was ‘negative’. Masks didn’t work. We knew this before the trial was published because we were told so on social media. The authors were reported by the media to be struggling to find a major journal for their trial. Journals weren’t proving brave enough to publish the study, said the authors, and they didn’t make a preprint available.
“When the mythical trial was finally published last week in the Annals of Internal Medicine we didn’t need to read it. We already knew its damning verdict on mask wearing. Social media told us as much. Eminent professors of evidence based medicine, Carl Heneghan and Tom Jefferson, confirmed this in an article for the Spectator.
“Except that if you read the published paper you find almost the exact opposite. The trial is inconclusive rather than negative, and it points to a likely benefit of mask wearing to the wearer – it did not examine the wider potential benefit of reduced spread of infection to others – and this even in a population where mask wearing isn’t mandatory and prevalence of infection is low. This finding is in keeping with summaries of evidence from Cochrane.”
A disagreement among experts, especially about interpretation of a study, is a common occurrence. It is the usual business of science, the BMJ editorial continues:
“Only, Facebook didn’t see it that way. The social media platform that allows statements about injecting bleach to prevent COVID-19, as well as calls to behead the leading US expert on pandemics, decreed that Heneghan and Jefferson should be censured for misinformation after they reposted their Spectator article on the site.
“It is possible to disagree with Heneghan and Jefferson about the robustness and interpretation of the DANMASK-19 trial – which I do – and still believe it is wrong that their opinion of it was marked as ‘false information’. It seems 2020 is Orwell’s 1984, where the boundaries of public discourse are governed by multibillion dollar corporations (in place of a totalitarian regime) and secret algorithms coded by unidentified employees.
“Where is Facebook’s accountability for the lies and damaging misinformation that it has peddled on controversial topics such as mental health and suicides, minorities and vaccines?”
The problem, Kamran Abbasi argues in the BMJ editorial, is less that Facebook and other social media decide what is published on their platforms – all publications do that. “It is more that Facebook in particular purports to allow freedom of speech on its platform but acts selectively, seemingly without logic, consistency or transparency. That is how control of facts and opinions furthers hidden agendas and manipulates the public.”
The full British Medical Journal editorial can be accessed via the link at the bottom.
Here's how to think about the Danish mask study
An analysis written by published by Dr Vinay Prasad in MedPage Today on 18 November 2020, looks at what the DANMASK-19 trial showed and didn't show about mask use and COVID-19:
“I was drawn to science and medicine because of all human endeavours, ours is one where smart people can say, ‘I don't know’. We don't stop there. We run a study or experiment that helps us know more. That is what makes what we do different than other human endeavours.
“I start then with a humility as I take on the Danish Mask Study in the Annals of Internal Medicine. This is a 4,800-person randomized trial that took place in the spring and early summer in Denmark.
“The trial was run at a time where most Danes did not wear masks when they left their house. It told participants to practice social distancing and randomly assigned them with the advice to wear a mask (and even gave them 50 surgical masks), advising them to change it after every 8 hours of use, or gave them no advice to wear mask, and followed them to see how many acquired SARS-CoV-2 by PCR or antibody testing.
“The answer was a nearly identical proportion – 42 of 2,393 people (1.8%) in the mask group and 53 of 2,470 (2.1%) in the no-mask group. The difference was not statistically significant.
Prasad does on to consider some of the criticism of the study, and in general does not find the research problematic. He continues:
What does the trial show?
“The Danish trial shows that this specific mask recommendation (plus a box of masks) made during the SARS-CoV-2 pandemic, with background rates of 2% PCR acquisition, failed to show that mask wearing reduces risk by 50%. In places where there is modest SARS-CoV-2 transmission (like Denmark during these months), there is insufficient evidence to suggest wearing a mask as you go about daily errands will protect you from infection. That is good to know!”
What doesn't the trial show?
“The trial is not able to assess the claim, ‘My mask protects you, not me’. The way to test this claim would be to randomise clusters or groups of people. Perhaps by city or county, and ask if mask mandates slow spread across all folks who live in that area. To my knowledge there has never been such a study, and while this message is popular and plausible, we should be willing to say, "I don't know for sure if it is true."
What the trial really means?
“Above all else, the Danish trial shows randomised trials are possible and desperately needed. We need these studies now than ever. Let's be honest. Masks have become a hot-button political issue. They are increasingly a badge symbolising who one voted for. This is a terrible consequence of bad leadership and caustic, polarised social media posts – yes, unfortunately, by both proponents and opponents of masks.
“The trials we need right now are cluster randomised trials to test messaging strategies. Is SARS-CoV-2 transmission slowed in counties/cities where we (a) advise people to wear a cloth mask because it's the patriot thing to do (b) advise them to wear a cloth mask because it may protect others (c) advise people to wear surgical masks and distribute households a box (d) advise masks indoors only, but no need to wear a mask outdoors, or (e) no additional comments made by officials. There are many important testable questions.
Should the trial have been published?
Prasad continues: “Some have turned to social media to ask why a trial that may diminish enthusiasm for masks and may be misinterpreted was published in a top medical journal.
“Woah! First, of all, I am prepared to die on the hill that science means publishing the results of truthful experiments no matter what they show. We can acknowledge limits, but we can never suppress results. Second, in today's environment of rampant conspiracy theories, watching doctors openly discuss not publishing results seems to be … I can't think of a polite word.” Masks should not be made political, Prasad insists” “If one wishes to be a public health expert for all Americans, one cannot be a naked political actor online.”
Why so much criticism?
“I think we have to consider why we have such strong emotions toward masks. Amongst all the non-pharmacologic things one can do to potentially slow the spread of SARS-CoV-2, masks dominate the conversation. Handwashing has faded entirely from the discussion.
“One possibility is that masks are a clear and visible symbol, and handwashing is invisible. We have to consider the fact that we are reacting to this study on an emotional level, and those emotions are also preventing us from doing additional trials (such as the cluster trials I describe above) that might yield useful insights.”
Final thoughts?
Prasad writes: “I have a few. Masks are not parachutes. Their effect size at best is going to be modest. Every time you muster the breath to advise someone to wear a mask, advise handwashing, distancing and avoiding indoor gatherings too.” Also, people should put masks in perspective – “Let us save our breath for the recommendations that matter.”
In short, Prasad concludes: “The Danish mask study doesn't answer every question, but it was well done, thoughtful, useful and what we need more of. I commend Christine Laine and her fellow editors at the Annals of Internal Medicine for publishing it.
“The investigators will not get the praise they deserve, but I will praise them. They are scientists, and there are still a few of us left breathing who can recognise that.
Dr Vinay Prasad is a haematologist-oncologist and associate professor of medicine at the University of California San Francisco.
The full MedPage Today analysis can be accessed via the link below.
Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers – A Randomised Controlled Trial
Annals of Internal Medicine. Published on 18 November 2020
Authors
Henning Bundgaard, Johan Skov Bundgaard, Daniel Emil Tadeusz Raaschou-Pedersen, Christian von Buchwald, Tobial Todsen, Jakob Boesgaard Norsk, Mia M Pries-Heje, Christoffer Rasmus Vissing, Pernille B Nielsen, Ulrik C Winslow, Kamille Fogh, Rasmus Hasselbalch, Jonas H Kristensen, Anna Ringgaard, Mikkel Porsborg Andersen, Nicole Bakkegard Goecke, Ramona Trebbien, Kerstin Skovgaard, Thomas Bendield, Henrik Ullum, Christian Torp-Pedersen and Kasper Iversen
The authors are from university hospitals in Copenhagen, Denmark.
Abstract
Observational evidence suggests that mask wearing mitigates transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It is uncertain if this observed association arises through protection of uninfected wearers (protective effect), via reduced transmission from infected mask wearers (source control), or both.
Objective
To assess whether recommending surgical mask use outside the home reduces wearers' risk for SARS-CoV-2 infection in a setting where masks were uncommon and not among recommended public health measures.
Design
Randomised controlled trial (DANMASK-19 [Danish Study to Assess Face Masks for the Protection Against COVID-19 Infection]). (ClinicalTrials.gov: NCT04337541)
Setting and participants
Denmark, April and May 2020. Participants were adults spending more than 3 hours per day outside the home without occupational mask use.
Intervention
Encouragement to follow social distancing measures for coronavirus disease 2019, plus either no mask recommendation or a recommendation to wear a mask when outside the home among other persons together with a supply of 50 surgical masks and instructions for proper use.
Measurements
The primary outcome was SARS-CoV-2 infection in the mask wearer at 1 month by antibody testing, polymerase chain reaction (PCR), or hospital diagnosis. The secondary outcome was PCR positivity for other respiratory viruses.
Results
A total of 3,030 participants were randomly assigned to the recommendation to wear masks, and 2,994 were assigned to control; 4,862 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.
Limitation
Inconclusive results, missing data, variable adherence, patient-reported findings on home tests, no blinding, and no assessment of whether masks could decrease disease transmission from mask wearers to others.
Conclusion
The recommendation to wear surgical masks to supplement other public health measures did not reduce the SARS-CoV-2 infection rate among wearers by more than 50% in a community with modest infection rates, some degree of social distancing, and uncommon general mask use. The data were compatible with lesser degrees of self-protection.
[link url="https://www.forbes.com/sites/leahrosenbaum/2020/11/18/lead-researcher-behind-controversial-danish-study-says-you-should-still-wear-a-mask/?sh=53397ae339e7"]The Forbes article – Lead Researcher Behind Controversial Danish Study Says You Should Still Wear A Mask[/link]
[link url="https://www.bmj.com/content/371/bmj.m4586"]British Medical Journal – The curious case of the Danish mask study[/link]
[link url="https://www.medpagetoday.com/blogs/vinay-prasad/89778"]MedPage Today analysis – Here's How to Think About the Danish Mask Study[/link]
[link url="https://www.acpjournals.org/doi/10.7326/M20-6817"]Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers – A Randomized Controlled Trial[/link]