# Danish study shows no significant reduction of Covid-19 in wearers of surgical masks

Discussion in 'Hangar Talk' started by PeterNSteinmetz, Nov 19, 2020.

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1. ### David MegginsonLine Up and Wait

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x = y ÷ 5

2. ### overdrive148En-Route

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I'm also young, and also have a low chance of dying from it.

I think the problem is that it's been compared to the flu so often that people think that there's no long term effects on you because the flu usually doesn't do that. You get the flu and then you get better and it's a non-event afterwards for most people.

Based on what I've read so far, there's other lasting issues that cause issues well beyond being infected and "recovering" enough not to die in the hospital. Heart and lung issues are the big ones. I don't hope for those people to get COVID because of their attitudes, but I wish they would get with the program and help create a unified front so we can put COVID behind us and get back to our lives.

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3. ### smvPattern Altitude

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Where is the multiplication ("times`) in that equation?

4. ### Matthew RogersLine Up and Wait

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Start with 100 particles in a person's breath. Block 80% of them with one mask as one person exhales. You have 20 particles left in the air. Block 80% of those 20 particles in the air with the second person wearing a mask and you have 4 particles.
The hypothetical situation proposed was whether it made a difference if one person was wearing a mask or if both people were wearing masks. I showed it with masks that filtered 50% or 80% of particles. You brought up the 80% case.
One person wearing a mask = 20 particles inhaled
Both people wearing masks = 4 particles inhaled
Inhaling 4 particles vs 20 particles is 5 times lower virus transmission. Or to reverse it, if only one person is wearing a mask, it results in a 5 times greater virus transmission. Simple case, lots of controls.

Sometimes I even math, dude

Last edited: Nov 20, 2020 at 5:09 PM
5. ### bflynnFinal Approach

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How many particles does it take to infect someone?

BTW, I suspect there is an order of magnitude thing going on with your example. Epidemically speaking, there is a huge difference between 4 and 20, there isn’t much of one between 4 million and 20 million.

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6. ### Matthew RogersLine Up and Wait

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I heard that it takes on the order of 100-300 virons (in a short-ish period of time) to infect. But I don't have the source. Fewer than that and the average immune system clean them up. More than that and a few slip past and infect cells, leading to a few million in short order.

7. ### overdrive148En-Route

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I think it's something called viral load and having more virus exposure make your case of COVID worse. Can't point to a specific source but I've heard it frequently.

8. ### WannFlyFinal Approach

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Just checking if this thread is allowing replies

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9. ### PPC1052En-Route

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Common sense is not in and of itself the scientific method. It's fine for a starting hypothesis. But we test those hypotheses to see if they are true. Or actually, we test to see if we can prove the hypothesis false.

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10. ### PPC1052En-Route

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That may be true, but does not negate the conclusion set forth by Peter in his original post.

11. ### David MegginsonLine Up and Wait

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(edited) Do you honestly not understand what the original poster meant when they wrote that? Nitpicking language isn't the same as debating.

Last edited: Nov 20, 2020 at 9:23 PM
12. ### Matthew RogersLine Up and Wait

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Just saying - direct from the CDC report this week. Direct evidence that mask mandates result in lower COVID transmission and infection. And lots of PHD and MD authors, since I know you guys like to see that.

Weekly Report (MMWR)
Early Release / November 20, 2020 / 69
Miriam E. Van Dyke, PhD1; Tia M. Rogers, PhD1; Eric Pevzner, PhD2; Catherine L. Satterwhite, PhD3; Hina B. Shah, MPH4; Wyatt J. Beckman, MPH4; Farah Ahmed, PhD5; D. Charles Hunt, MPH4; John Rule6(View author affiliations)

View suggested citation
Summary

What is added by this report?

The governor of Kansas issued an executive order requiring wearing masks in public spaces, effective July 3, 2020, which was subject to county authority to opt out. After July 3, COVID-19 incidence decreased in 24 counties with mask mandates but continued to increase in 81 counties without mask mandates.

What are the implications for public health practice?

Countywide mask mandates appear to have contributed to the mitigation of COVID-19 transmission in mandated counties. Community-level mitigation strategies emphasizing use of masks, physical distancing, staying at home when ill, and enhanced hygiene practices can help reduce the transmission of SARS-CoV-2.

https://www.cdc.gov/mmwr/volumes/69/wr/mm6947e2.htm

13. ### David MegginsonLine Up and Wait

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The conclusion he quoted was that masks make no difference when you're already following other public health measures like 2 metre physical distancing. That's not news. Masks are for when you can't distance, like in a store or office or even a crowded sidewalk. They're not as effective as distancing, but still better than nothing.

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14. ### PeterNSteinmetzPattern AltitudePoA Supporter

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This is one of the studies that needs to considered objectively in the context of all the other studies out there. There are over 100 now. The scientific reviews try to do this. And as summarized on my medical interest page, they are overall about 50/50 on the efficacy of the general public being told to wear masks to slow the spread of Covid-19. And that is prior to the recent Danish study which I started this thread with.

If you want to objectively read those reviews, then it might be productive to discuss and possibly look at individual articles in that context. Without doing so, this is just picking and choosing specific studies to support a particular point.

There is lots of evidence on both sides of this issue, the trick in science is objectively evaluating the totality of the evidence in light of each items strengths and weaknesses. Doing that for over 100 articles is a lot of work and not likely the sort of thing most posters here are inclined to do. That is why I suggest first objectively reading the reviews.

15. ### Matthew RogersLine Up and Wait

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We will unfortunately see whether the 6 foot rule even applies this winter. If the virus is airborne for long enough to infect people at greater distances, we will see more spread as there are more people indoors for longer periods of time, regardless of whether they are keeping 6 feet apart. Here’s to hoping that it actually drops out of the air in only 6 feet.

16. ### David MegginsonLine Up and Wait

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You're right that it's a challenge, because people don't live their lives in sterile lab conditions. Canadian public health authorities hesitated to recommend mask wearing during the early months of the pandemic because of the fear that an exaggerated sense of invulnerability (masks don't provide the same protection as distancing) would trigger riskier behaviour that would cause more harm than the masks did good, due to https://en.wikipedia.org/wiki/Risk_compensation. That was a legitimate concern, but the experience in most jurisdictions has been that indoor public mask mandates have reduced community transmission significantly, and as that's become clear, more and more public health authorities have come on board. But public health is always as much an art as a science, because every new rule (or every rule removed) changes underlying human behaviour in unpredictable ways, so there's as much "soft" (social) science as "hard" science behind their work.

17. ### PPC1052En-Route

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Agreed.
Actually, I think the point is that the mask makes little difference to the wearer of the mask. It does not suggest that it does not prevent transmission to others. A hypothesis that I have is that aerosolized moisture exhaled by infected individuals will eventually suspend in the air, and after a sufficient period of time, the exhaled product will saturate a body of air within a confined space. Aerosolized moisture will absolutely pass through the pores in the mask. So, if there is a sufficient saturation of aerosolized moisture in a body of air within a confined space, masks will be useless to protect the wearer. But masks will prevent large droplets and slow airflow such that it will help limit the spread to others. Just my hypothesis.

Last edited: Nov 20, 2020 at 7:03 PM
18. ### PeterNSteinmetzPattern AltitudePoA Supporter

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In order to have a reasonable objective discussion about the results of any study you might cite to support this claim about causing reduced community transmission, it really is necessary to read the reviews and consider such studies in the light of all available evidence. I take it you haven't done that yet.

19. ### Matthew RogersLine Up and Wait

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Edit - I didn’t read them all yet, but I’ll take your word for the answers to my questions.

But does this show that people in this country are unwilling to follow mask mandates, or that masks don’t work? Does any of the data in the studies show that the mask mandates were actually followed by a large enough percentage of the population to be successful, or if not did that skew the results? If not, then the problem is not the masks, but the enforcement of the mandate perhaps. We all know that a significant percentage of the population think the virus is a hoax and so are unwilling to wear a mask, mandate or not, so that kinda skews the data into showing that masks are not as effective as they could be if everyone wore them correctly all the time when mandated.

This could explain the Hong Kong success - a place where mask wearing was common before 2020. A mask mandate is a no-brainer for their population and I would bet that there would be little need for enforcement to achieve near perfect compliance.

20. ### PaulSTouchdown! Greaser!

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"Hong Kong has suspended in-person classes for lower primary school students after the city’s top health official said the coronavirus situation in the city was “severe”."

21. ### PeterNSteinmetzPattern AltitudePoA Supporter

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The reviews deal with the totality of the data, including the experiences in Hong Kong, etc. Perhaps read them objectively. As I noted above, without that, picking and choosing this study or another to support a particular point is not the way to reach valid scientific conclusions.

22. ### MountainDudePre-takeoff checklist

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There will be 2000 excess deaths due to COVID today (relative to the 5 year average). You can try to justify it any way you want, but those 2000 people would live tomorrow if it was not for COVID. Math does not lie.

23. ### MountainDudePre-takeoff checklist

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See post #142. You can find the data on NYT.

24. ### Matthew RogersLine Up and Wait

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25. ### David MegginsonLine Up and Wait

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Quite right -- I mentioned air circulation earlier as well. The biggest risk is when you're exposed to an infected person for a long time, e.g. chatting with someone face-to-face, sitting at a nearby desk in an office, or near another table in a restaurant. I don't think we'll see a lot of transmission from people just passing each-other in the aisles of stores for a few seconds (assuming they're wearing masks), but like I mentioned in another post, there's still a lot of guesswork involved with a disease that the scientific community has been studying seriously for less than a year. Personally, I won't be dining in in restaurants, drinking in bars, or going to theatres — even with masks and distancing — until the pandemic is over, or at least, mostly over, for precisely the reasons you mentioned. Masks are for risk reduction, not risk elimination.

I was in West Africa doing work with the U.N. (note: I'm a layperson, not a doctor or nurse or health researcher) when the Ebola vaccine was announced in summer 2015. It was a wonderful moment for everyone there, but it didn't magically end the outbreak. The next day, all the same public health measures were in place in Conakry as had been the day before, and I still had to run a gauntlet of tests at 3 different airports to be allowed to return to Canada, and then I had to self monitor and report to public health for weeks after I got back. This isn't going to be over soon, people, but some day it will be, and until then, every little bit of hope and kindness is precious.

26. ### RavioliFinal ApproachPoA Supporter

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Math may not lie, and Mathematicians may not lie, but you're using Statistics which is 100% the "science" of finding "facts" and "trends" to support a preconceived notion to the exclusion of all others.

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27. ### TarheelpilotEn-Route

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What do you propose we should do about it ?

actually never mind. I really don’t care what you think.

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28. ### bdtazPre-Flight

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If one reads the recognized limitations they seem to make the "Correlation/causation" relationship a bit less clear than the "headline"

It also seems to be a relatively small numerical difference per 100,000. At the end of their tracking 16 cases per 100,000 among mandated counties and 12 per 100,000 among nonmandated counties. It seems it would be very possible that a difference of 4 persons/100,000 could be attributed to something else or simply too small for the sample size.

They also reference an earlier study about AZ that begs a question now: If masks were the main reason behind a reduction of cases as described in the study, why are cases and hospitalizations increasing even though no changes have been made in the mask mandates?

The first response is "People are dropping their guard" but personal observance here in AZ is when the cases/hospitalizations were decreasing in AUG, roughly 80% of the people observed in my local grocery store were masked. On my visit this AM, pretty close to 100% wore masks.

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29. ### Matthew RogersLine Up and Wait

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30. ### wsuffaTouchdown! Greaser!

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Not even this winter. I was at a place last night that has the tables ~15 feet apart, limited diners, masks required when not eating/drinking, super cleanliness.... And there was a group of 6 at one table probably 45 feet from me who were carrying on loudly (a friend used the term 'is she going to lay an egg') without masks - and had quite a bit to drink. I was at a table at the back of the room under a ceiling air vent and wore a mask when no eating.... So I'm not too worried about my exposure... But the behavior of the otr group is exhibit #1 of why the state's are restricting restaurants again.

31. ### wsuffaTouchdown! Greaser!

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32. ### SaltyFinal ApproachPoA Supporter

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Before this thing, how often did your doctor see you with a mask on for a regular visit?

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33. ### TarheelpilotEn-Route

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That’s fine. Just keep on driving. I don’t want your help.

34. ### PeterNSteinmetzPattern AltitudePoA Supporter

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Yes, what you say makes sense to me, but to analyze this further I think we should breakdown the different routes of transmission, as they are not all equally likely.

So from the infected person (I) to the non-infected person (NI) there are at least 3 routes that I can think of right away.
1. Large drops such as those expectorated when singing loudly, yelling, etc.
2. Small respiratory droplets which tend to hang around in the air.
3. Direct contact transfer.

To get some rough idea of whether things would be asymmetric in this 2 people in a room scenario, we will need to account for how masks might interrupt each route of transmission as well as how probable those different routes are.

For each route:

1. A mask on I will definitely reduce the drops that get expelled toward NI. So how many of those would really end up affecting NI absent the mask? Presumably mostly those that land on their respiratory surfaces (RS), but some that land elsewhere on the body could be subsequently picked up by NI and then passed to their RS. The drops landing directly on RS would be interrupted by a mask on NI. It seems like there might be some asymmetry in this route of transmission, but that would depend on the relative efficacy of inhaling the drops versus touching your clothing or body where a drop landed. My understanding is that this large drop mode of transmission from person to person is considerably less likely than #2.

2. A mask on I or NI will likely decrease the amount of respiratory droplets landing directly on the RS of NI equally. The same factor of reduction from the mask would be present in either case. Some small fraction of respiratory droplets presumably land on NI and might be passed to their RS via contact. Thus this mode is likely to mostly symmetric. My understanding is that the inhalation of respiratory droplets is the primary mechanism of transmission of Covid-19.

3. Masks would have no likely effect on direct contact with other surfaces or the other party. Wearing a mask by NI might decrease their likelihood of transferring virions from their hands onto their RS, but this would depend on handling of the mask. Wearing a mask by I would not affect NI's chances of passing virions from their hands onto their RS.

So based on this simple analysis I would suggest that it is highly likely the effect of mask wearing in this 2 person room scenario would be mostly symmetric. The degree of asymmetry would be quite slight.

As you can see, it is probably difficult to predict this accurately based on in-vitro studies. Direct measurement would be best. I have been thinking a bit about how one might be able to do that with some models.

Now I have not analyzed this or the literature on this deeply, mostly because I was waiting for the results of the Danish study to spend further time on this issue. But now that that is out and makes this a more pertinent issue, I will probably dig further into this.

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35. ### SaltyFinal ApproachPoA Supporter

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Looks like you failed this time. Ironic, huh? Lol

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36. ### bdtazPre-Flight

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That would be a great question to ask them.

If the answer is "Well, I work in the very definition of "high risk environment" , have been properly trained in their use and limitations, and believe it offers me and you a small modicum of protection", great!

If they insist you wear one as well, fine. You can choose to do it or go elsewhere.

If their answer is "Science says they work, you know surgeons use them so there you go ", well, that's not quite as convincing....

37. ### Matthew RogersLine Up and Wait

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When presented with a high risk case (TB, measles, the act of intubation with any respiratory ailment), doctors did employ regular protective mask use. They very often wore gloves, even for regular visits like a physical, because more of the common vectors are blood borne, skin bacteria (MRSA, staph, etc), fluid borne (STDs and such), or parasitic (mites and icky crawly things). I have no data, but based on the high rates of mask wearing pre-2020 in places like Japan, I would imagine that doctors in those places wore masks for nearly every patient visit. And look how they have done in 2020, even with a population older than ours. Japan - 15 deaths/million. USA - 785 deaths/million.

That was before we were inundated with a virus that had such a high percentage of asymptomatic cases. 40% of cases walking around spewing out virus without ever knowing it.

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38. ### SaltyFinal ApproachPoA Supporter

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Make up your mind. I thought you wore a mask to protect the other person, not yourself......

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39. ### EdFredTaxi to Parking

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Math doesn't lie, but people do, and the NYT is not a reputable source. You still ignored the question. Not surprising considering the number you cherry picked.

Last edited: Nov 20, 2020 at 7:54 PM
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40. ### Matthew RogersLine Up and Wait

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No, I wear a good quality mask to protect myself, because I am also protecting 5 others, including my father who lives on my property and who had pancreatic cancer in Dec 2019 and chemo through June 2020. Protecting myself, is protecting them and protecting others in my town.

In the beginning (Feb-May), here in NY, I wore my full-face North-brand P100 respirator to the grocery store. Switched to a half mask respirator when cases went down, and then to good fitting N95 for trips and KN95 masks for outside outings. But I also had a some of this equipment in my commercial wood shop before the pandemic, so any extras were just stock for the shop PPE and worth the expense. What is \$300 in masks anyway compared to the expense of an illness these days? Plus, I have plenty to give out to others when they need them.
I am pretty sure that EdFred is not a reputable news source, so I can't trust what you say about the NYT.