[thatboy]

Can someone point me to the most definitive or best studies showing the efficacy of mask-wearing? I have a friend who is a bit on the conspiratorial side and is skeptical of all things "Fauci", among other things. In a nutshell he's an anti-masker. I have agreed to disagree with him, but would like to point him towards some well-reasoned and well-designed studies, meta-studies, or articles about mask wearing. I don't expect to change his mind, but would like to give it a reasonable shot.

One of his primary arguments is that the size of the virus is smaller than what can be filtered by most masks. My intuition is that while this may be technically true, the virus itself is nevertheless largely attached and transported by droplets (even if microscopic) which themselves are large enough to be caught by a filter. Thus a mask has efficacy to some significant degree, even if not perfect. Two people wearing masks further compounds the efficacy. Is my characterization accurate or am I off-base?

Also, Taleb talked about some non-linear compounding of mask-wearing efficacy. I don't understand the math. Is it a reasonable conclusion?

Thanks

[thatboy]

Can someone point me to the most definitive or best studies showing the efficacy of mask-wearing? I have a friend who is a bit on the conspiratorial side and is skeptical of all things "Fauci", among other things. In a nutshell he's an anti-masker. I have agreed to disagree with him, but would like to point him towards some well-reasoned and well-designed studies, meta-studies, or articles about mask wearing. I don't expect to change his mind, but would like to give it a reasonable shot.

One of his primary arguments is that the size of the virus is smaller than what can be filtered by most masks. My intuition is that while this may be technically true, the virus itself is nevertheless largely attached and transported by droplets (even if microscopic) which themselves are large enough to be caught by a filter. Thus a mask has efficacy to some significant degree, even if not perfect. Two people wearing masks further compounds the efficacy. Is my characterization accurate or am I off-base?

Also, Taleb talked about some non-linear compounding of mask-wearing efficacy. I don't understand the math. Is it a reasonable conclusion?

Thanks

[Snorlax94]

Maybe someone here will dig up the old research we’ve already hashed. I’m a bit less patient.

Does your friend believe he is exempt and can walk barefoot into a restaurant that says no shirt, no shoes, no service? Do society’s and business property rights not apply to him?

When he goes to a hospital to visit a friend who is gravely ill, does he refuse to wash his hands and demand to read the research demonstrating the efficacy of hand washing, then insist on receiving proof that the soap and water at the hospital is the exact same as in the study?

If he wants to sell food in the street, does he refuse to permit inspectors to review his sanitation methods — that he washes his hands, that chicken is properly heated to kill bacteria, that rat feces is not sprinkled all over his pantry, then grabs his gun and claims a tyrranical government is not letting him sell his Freedom Food?

[Snorlax94]

Maybe someone here will dig up the old research we’ve already hashed. I’m a bit less patient.

Does your friend believe he is exempt and can walk barefoot into a restaurant that says no shirt, no shoes, no service? Do society’s and business property rights not apply to him?

When he goes to a hospital to visit a friend who is gravely ill, does he refuse to wash his hands and demand to read the research demonstrating the efficacy of hand washing, then insist on receiving proof that the soap and water at the hospital is the exact same as in the study?

If he wants to sell food in the street, does he refuse to permit inspectors to review his sanitation methods — that he washes his hands, that chicken is properly heated to kill bacteria, that rat feces is not sprinkled all over his pantry, then grabs his gun and claims a tyrranical government is not letting him sell his Freedom Food?

[thatboy]

Those are good questions. He lives in southern California, whereas I'm up north, so I'm not sure how he behaves in everyday life with respect to masks (he was an old roommate many years ago, but I haven't hung out with him since well before all the COVID issues). I'm just repeating some things he has told me over a few calls and texts. I will ask him next time I talk to him. But I will say that despite his beliefs he's not the kind of person to be confrontational. He's not the kind of guy who is going to get on an airplane and refuse to wear a mask, for example. To my knowledge he follows the rules, so to speak; he just doesn't believe in them.

[thatboy]

Those are good questions. He lives in southern California, whereas I'm up north, so I'm not sure how he behaves in everyday life with respect to masks (he was an old roommate many years ago, but I haven't hung out with him since well before all the COVID issues). I'm just repeating some things he has told me over a few calls and texts. I will ask him next time I talk to him. But I will say that despite his beliefs he's not the kind of person to be confrontational. He's not the kind of guy who is going to get on an airplane and refuse to wear a mask, for example. To my knowledge he follows the rules, so to speak; he just doesn't believe in them.

[BostonCard]

There is no single definitive study.  The best one I know of is from a few months ago and was published in the Lancet, a meta analysis evaluating both the effect of social distancing and mask wearing.

https://www.thelancet.com/article/S0140-...9/fulltext

BC

[BostonCard]

There is no single definitive study.  The best one I know of is from a few months ago and was published in the Lancet, a meta analysis evaluating both the effect of social distancing and mask wearing.

https://www.thelancet.com/article/S0140-...9/fulltext

BC

[oldalum]

I and I think others have mentioned in previous threads a few contact tracing case studies in which masks seemed to be protective (a full South Korean mask wearing evacuation flight with something like 6 not-known-at-the-time asymptomatic but infectious people who only infected one other passenger over 11 hours, someone who was not sitting near any of the infected people but took off her mask in a restroom used by one of the infected people), a McDonald's or something in South Korea in which one infected person who sat under an air conditioner for 2 hours infected numerous other customers who came and went but not the two employees who were there for 8 hours and wore masks the whole time). No one of these case studies is definitive (e.g., airplane bathroom transmission could have been fomite) but together they are fairly convincing, at least to me, that masks (especially N95) are highly protective against aerosol infection and transmission. Which makes sense, that is what they are supposed to do. Keep in mind that we can't do randomized controlled trials on effectiveness of masks; the evidence is going to be imperfect.

[oldalum]

I and I think others have mentioned in previous threads a few contact tracing case studies in which masks seemed to be protective (a full South Korean mask wearing evacuation flight with something like 6 not-known-at-the-time asymptomatic but infectious people who only infected one other passenger over 11 hours, someone who was not sitting near any of the infected people but took off her mask in a restroom used by one of the infected people), a McDonald's or something in South Korea in which one infected person who sat under an air conditioner for 2 hours infected numerous other customers who came and went but not the two employees who were there for 8 hours and wore masks the whole time). No one of these case studies is definitive (e.g., airplane bathroom transmission could have been fomite) but together they are fairly convincing, at least to me, that masks (especially N95) are highly protective against aerosol infection and transmission. Which makes sense, that is what they are supposed to do. Keep in mind that we can't do randomized controlled trials on effectiveness of masks; the evidence is going to be imperfect.

[fullmetal]

You're correct that viral particles do not float freely in the air.  They're always suspended in moisture droplets that are easily captured by exhalers' masks (or at least slowed down), if they're N95-grade.  Even if the masks aren't N95-grade, slowing down the exhalations is big. It prevents droplets from traveling very far, which is where the effectiveness of social distancing comes into play.  

But yeah, reducing the speed of exhalations is a big deal in particle travel/flow.  And inhaling with a mask definitely helps filter out particles assuming the mask is of sufficient grade.

They figured this out in China when initial frontline medical staff in the covid crisis were also catching the disease and dropping like flies.  Once PPE became standard, the rate at which medical staff were getting sick/dying decreased rapidly.  I think the Italian healthcare staff benefited from that initial experience of viral contagion before and after PPE standards.

[fullmetal]

You're correct that viral particles do not float freely in the air.  They're always suspended in moisture droplets that are easily captured by exhalers' masks (or at least slowed down), if they're N95-grade.  Even if the masks aren't N95-grade, slowing down the exhalations is big. It prevents droplets from traveling very far, which is where the effectiveness of social distancing comes into play.  

But yeah, reducing the speed of exhalations is a big deal in particle travel/flow.  And inhaling with a mask definitely helps filter out particles assuming the mask is of sufficient grade.

They figured this out in China when initial frontline medical staff in the covid crisis were also catching the disease and dropping like flies.  Once PPE became standard, the rate at which medical staff were getting sick/dying decreased rapidly.  I think the Italian healthcare staff benefited from that initial experience of viral contagion before and after PPE standards.

[M T]

You're correct that viral particles do not float freely in the air.  They're always suspended in moisture droplets that are easily captured by exhalers' masks (or at least slowed down), if they're N95-grade. 

That's not quite true.  When expelled, as best we know, the virus are in moisture droplets.  But anything less than 100 microns in diameter (depending on humidity & temp.) dries out (the water evaporates) before hit falls to the floor.  The result is called a droplet nuclei, typically less than 5 microns in size and can stay aloft for hours.   Some studies

• The size and concentration of droplets generated by coughing in human subjects (My old posts should have links to more articles.)  
  
• On coughing and airborne droplet transmission to humans (a modeling study) 
  
• COVID-19. Transport of respiratory droplets in a microclimatologic urban scenario (modeling study)
  

While N95 & KN95 are spec'ed in terms of blocking 0.3 micron particles, that's about the size they are least effective at.  I believe that's why 0.3 microns was chosen for measuring effectiveness.  Smaller particles are captured by (typically) electrostatic attraction to the fibers in the mask.  From a 1998 study:

N95 respirators made by different companies were found to have different filtration efficiencies for the most penetrating particle size (0.1 to 0.3 micron), but all were at least 95% efficient at that size for NaCl particles. Above the most penetrating particle size the filtration efficiency increases with size; it reaches approximately 99.5% or higher at about 0.75 micron. Tests with bacteria of size and shape similar to Mycobacterium tuberculosis also showed filtration efficiencies of 99.5% or higher. Experimental data were used to calculate the aerosol mass concentrations inside the respirator when worn in representative work environments. The penetrated mass fractions, in the absence of face leakage, ranged from 0.02% for large particle distributions to 1.8% for submicrometer-size welding fumes.

I haven't kept up with recent studies on mask effectiveness.  The problem is not the filtration of the mask, but the wearer and how it fits them.  Not wearing a mask is obviously the biggest issue.  Surveys of usage usually depend upon self-reporting.  Once a person is actually wearing a mask, the next question is fit.  A bandana has basically no fit.  It might capture ballistic droplets, but other droplets will escape or be inhaled where the mask isn't held against the face.   Some earloop masks will allow particles to exit or enter toward the ears.  Especially the homemade masks without nose clips will tend to let particles enter/exit toward the eyes.   Even small openings dramatically decrease the effectiveness of a (K)N95 mask when the particles are uniform around the mask.

I really wish all the health agencies were collecting data on the people that get COVID.  Even self-reported mask usage or glasses/shield usage and other exposure information is more info than none.   California could have 800K data points instead of zero.

[M T]

You're correct that viral particles do not float freely in the air.  They're always suspended in moisture droplets that are easily captured by exhalers' masks (or at least slowed down), if they're N95-grade. 

That's not quite true.  When expelled, as best we know, the virus are in moisture droplets.  But anything less than 100 microns in diameter (depending on humidity & temp.) dries out (the water evaporates) before hit falls to the floor.  The result is called a droplet nuclei, typically less than 5 microns in size and can stay aloft for hours.   Some studies

• The size and concentration of droplets generated by coughing in human subjects (My old posts should have links to more articles.)  
  
• On coughing and airborne droplet transmission to humans (a modeling study) 
  
• COVID-19. Transport of respiratory droplets in a microclimatologic urban scenario (modeling study)
  

While N95 & KN95 are spec'ed in terms of blocking 0.3 micron particles, that's about the size they are least effective at.  I believe that's why 0.3 microns was chosen for measuring effectiveness.  Smaller particles are captured by (typically) electrostatic attraction to the fibers in the mask.  From a 1998 study:

N95 respirators made by different companies were found to have different filtration efficiencies for the most penetrating particle size (0.1 to 0.3 micron), but all were at least 95% efficient at that size for NaCl particles. Above the most penetrating particle size the filtration efficiency increases with size; it reaches approximately 99.5% or higher at about 0.75 micron. Tests with bacteria of size and shape similar to Mycobacterium tuberculosis also showed filtration efficiencies of 99.5% or higher. Experimental data were used to calculate the aerosol mass concentrations inside the respirator when worn in representative work environments. The penetrated mass fractions, in the absence of face leakage, ranged from 0.02% for large particle distributions to 1.8% for submicrometer-size welding fumes.

I haven't kept up with recent studies on mask effectiveness.  The problem is not the filtration of the mask, but the wearer and how it fits them.  Not wearing a mask is obviously the biggest issue.  Surveys of usage usually depend upon self-reporting.  Once a person is actually wearing a mask, the next question is fit.  A bandana has basically no fit.  It might capture ballistic droplets, but other droplets will escape or be inhaled where the mask isn't held against the face.   Some earloop masks will allow particles to exit or enter toward the ears.  Especially the homemade masks without nose clips will tend to let particles enter/exit toward the eyes.   Even small openings dramatically decrease the effectiveness of a (K)N95 mask when the particles are uniform around the mask.

I really wish all the health agencies were collecting data on the people that get COVID.  Even self-reported mask usage or glasses/shield usage and other exposure information is more info than none.   California could have 800K data points instead of zero.

[BostonCard]

MT, I would highly recommend reading this Atlantic article.

https://www.theatlantic.com/ideas/archiv...ks/613375/

Americans are figuring out how to live with a deadly new virus now, just as gay men did in the early years of AIDS. Abstinence from sex wasn’t sustainable, and condoms became a ticket to greater sexual freedom. Likewise, Americans can’t abstain from human interaction forever, and widespread masking may be a ticket to more social and economic freedom. But trying to shame people into wearing condoms didn’t work—and it won’t work for masks either.

Empathy has its own kind of power. Acknowledging what people dislike about a public-health strategy enables a connection with them rather than alienating them further. And when the barriers are understood, they become addressable.

Good luck.

BC

---

Also, this thread from the author:

[tweet]https://twitter.com/JuliaLMarcus/status/1284203364818079744[/tweet]

BC

[BostonCard]

MT, I would highly recommend reading this Atlantic article.

https://www.theatlantic.com/ideas/archiv...ks/613375/

Americans are figuring out how to live with a deadly new virus now, just as gay men did in the early years of AIDS. Abstinence from sex wasn’t sustainable, and condoms became a ticket to greater sexual freedom. Likewise, Americans can’t abstain from human interaction forever, and widespread masking may be a ticket to more social and economic freedom. But trying to shame people into wearing condoms didn’t work—and it won’t work for masks either.

Empathy has its own kind of power. Acknowledging what people dislike about a public-health strategy enables a connection with them rather than alienating them further. And when the barriers are understood, they become addressable.

Good luck.

BC

---

Also, this thread from the author:

[tweet]https://twitter.com/JuliaLMarcus/status/1284203364818079744[/tweet]

BC

[magnus]

@thatboy, this might be useful

https://preventepidemics.org/spanish/cov...october-2/

Talks about viral load and masks.

[magnus]

@thatboy, this might be useful

https://preventepidemics.org/spanish/cov...october-2/

Talks about viral load and masks.

[CompSci87]

Sorry everyone who is being serious, but thatboy's username keeps making this song go through my head.

https://www.youtube.com/watch?v=lW5D7HpYhBU

[CompSci87]

Sorry everyone who is being serious, but thatboy's username keeps making this song go through my head.

https://www.youtube.com/watch?v=lW5D7HpYhBU

[thatboy]

Sorry everyone who is being serious, but thatboy's username keeps making this song go through my head.

I've never heard that song before, actually. I took my name from the old television show That Girl starring Marlo Thomas. I have no idea why I was thinking of that show when I signed up, but that's the etymology of my username -- with the obvious male adaptation.

[thatboy]

Sorry everyone who is being serious, but thatboy's username keeps making this song go through my head.

I've never heard that song before, actually. I took my name from the old television show That Girl starring Marlo Thomas. I have no idea why I was thinking of that show when I signed up, but that's the etymology of my username -- with the obvious male adaptation.

[CompSci87]

Sorry everyone who is being serious, but thatboy's username keeps making this song go through my head.

I've never heard that song before, actually. I took my name from the old television show That Girl starring Marlo Thomas. I have no idea why I was thinking of that show when I signed up, but that's the etymology of my username -- with the obvious male adaptation.

I remember that show! But I don't remember much about it other than that Marlo Thomas was cute.

[CompSci87]

Sorry everyone who is being serious, but thatboy's username keeps making this song go through my head.

I've never heard that song before, actually. I took my name from the old television show That Girl starring Marlo Thomas. I have no idea why I was thinking of that show when I signed up, but that's the etymology of my username -- with the obvious male adaptation.

I remember that show! But I don't remember much about it other than that Marlo Thomas was cute.

[DenverCard]

Happened upon this just scrolling around, and I don't think it has been cited here on the Cardboard.  For what it's worth:

https://www.nature.com/articles/d41586-0...ket-newtab

[DenverCard]

Happened upon this just scrolling around, and I don't think it has been cited here on the Cardboard.  For what it's worth:

https://www.nature.com/articles/d41586-0...ket-newtab

[OutsiderFan]

CDC study on mask wearing in Arizona.

https://www.cdc.gov/mmwr/volumes/69/wr/mm6940e3.htm

[OutsiderFan]

CDC study on mask wearing in Arizona.

https://www.cdc.gov/mmwr/volumes/69/wr/mm6940e3.htm