Author Topic: Masks  (Read 160868 times)

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Re: Masks
« Reply #61 on: June 12, 2020, 04:45:20 PM »
next week, iyh

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Re: Masks
« Reply #62 on: June 14, 2020, 06:03:48 PM »
Well, Dan asked for a summary of the article that @aygart posted, but it's disappeared.  And while I wrote a summary, this (better) summary with pictures has been published, but I'll paste mine anyway. Is this too long?

https://www.forbes.com/sites/alicegwalton/2020/06/13/face-masks-may-be-the-key-determinant-of-the-covid-19-curve-study-suggests/#44ac7f116497

Identifying airborne transmission as the dominant route for the spread of COVID-19, by Renyi Zhang and others, PNAS, published June 11, 2020

Short summary: Why did COVID-19 stop spreading so much faster in China than in Italy and the US?  And why did new cases plateau so much earlier in NYC than in the rest of the United States?  In both cases, the authors conclude that the onset of mandated face coverings made the difference, preventing tens of thousands of infections. 

Longer summary:
In China, the early response to the outbreak was SD, masks, extensive testing, and contact tracing, all put into effect simultaneously.  In China, the number of new cases increased for about 3 weeks after the lockdown, and had reached a plateau about a week after that. 

In NYC and Italy, the early response was hand washing, SD, stay-at-home, but masks were not required until a month had passed.  In these places, the number of new cases increased rapidly for about 4 weeks after the early SD requirement, and began to decrease only later, after the face covering requirement was implemented.

In the rest of the US the early response was hand washing, SD, stay-at-home and masks were not required, and the number of new cases were continuing to rise steeply (at the time they looked, May 9). 

The timing of these events suggests that mask-wearing was critical in decreasing the spread of coronavirus, quickly in China and after a delay in NYC.

A second piece of evidence they bring is from plotting the total cases in NYC, using a statistical technique called linear regression.  Their graph shows that if the original policy (SD, stay at home) had continued, the number of cases would have been much higher than it actually was.  The pivot point occurred on April 17, when masks were first required, and the caseload started to decline. 

Similarly, their comparison of new infections in NYC compared to the US as a whole (minus the NYC cases) shows that corona cases declined steeply after the April 17 mandated face covering, while new cases remained high during that time throughout the United States. 

Why would masks have such a dramatic effect?

Back in March, experts thought that the virus is communicated by droplets that we expel when we cough or sneeze.  These droplets are pulled down by gravity, so are usually found within 3 feet of a sick person, so we were advised to stay away from an obviously sick person and to wash our hands and keep them away from our face to avoid transferring a virus-containing droplet to our mouth, nose or eyes.  Masks were recommended only for the sick person themselves, to prevent their expelled droplets from contaminating others (WHO, April 6).

But later in April, scientists learned that there’s another way that virus can be expelled, in the form of much smaller particles, called aerosols, especially by people talking loudly or singing. 

You can visualize the difference by spraying a window cleaner and an air freshener on a mirror.  The window cleaner forms small droplets that soon start rolling down, attracted by gravity.  The air freshener forms an aerosol of tiny drops that remain where they fell on the mirror.  In fact, we spray air freshener into the air knowing that these miniscule particles – and their pleasant odor – will remain suspended in the air for quite some time.

The realization that viral particles were found in aerosols convinced the experts that the virus could be inhaled by someone who was more than 3 feet from an infected patient, or even in a room where an infected person had previously exhaled, and this led to expansion of the advice to wear masks: 

•   The knowingly infected should wear masks to avoid spreading their droplets and aerosols, which can contain virus. 
•   The unknowingly infected (that is, presymptomatic, when viral expulsion seems highest) should similarly wear masks to avoid spreading the virus. 
•   The healthy uninfected should wear masks to avoid inhaling the aerosols of the two previous groups. 

They conclude that “wearing of face masks in public corresponds to the most effective means to prevent interhuman transmission, and this inexpensive practice, in conjunction with extensive testing, quarantine, and contact tracking, poses the most probably fighting opportunity to stop the COVID-19 pandemic, prior to the development of a vaccine.”

My comment:
Finding that the number of cases in NYC began to decrease around the same time as mask wearing was required is not sufficient to conclude that mask wearing was responsible for the decrease.  Did people actually obey the mask-wearing regulation?  Were there other events that occurred around that time that contributed to the decline in new infections?  This paper provides evidence that mask-wearing is important, but it's weak evidence, and the argument could be strengthened by other research.

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Re: Masks
« Reply #63 on: June 14, 2020, 06:47:41 PM »
Well, Dan asked for a summary of the article that @aygart posted, but it's disappeared.  And while I wrote a summary, this (better) summary with pictures has been published, but I'll paste mine anyway. Is this too long?

https://www.forbes.com/sites/alicegwalton/2020/06/13/face-masks-may-be-the-key-determinant-of-the-covid-19-curve-study-suggests/#44ac7f116497

Identifying airborne transmission as the dominant route for the spread of COVID-19, by Renyi Zhang and others, PNAS, published June 11, 2020

Short summary: Why did COVID-19 stop spreading so much faster in China than in Italy and the US?  And why did new cases plateau so much earlier in NYC than in the rest of the United States?  In both cases, the authors conclude that the onset of mandated face coverings made the difference, preventing tens of thousands of infections. 

Longer summary:
In China, the early response to the outbreak was SD, masks, extensive testing, and contact tracing, all put into effect simultaneously.  In China, the number of new cases increased for about 3 weeks after the lockdown, and had reached a plateau about a week after that. 

In NYC and Italy, the early response was hand washing, SD, stay-at-home, but masks were not required until a month had passed.  In these places, the number of new cases increased rapidly for about 4 weeks after the early SD requirement, and began to decrease only later, after the face covering requirement was implemented.

In the rest of the US the early response was hand washing, SD, stay-at-home and masks were not required, and the number of new cases were continuing to rise steeply (at the time they looked, May 9). 

The timing of these events suggests that mask-wearing was critical in decreasing the spread of coronavirus, quickly in China and after a delay in NYC.

A second piece of evidence they bring is from plotting the total cases in NYC, using a statistical technique called linear regression.  Their graph shows that if the original policy (SD, stay at home) had continued, the number of cases would have been much higher than it actually was.  The pivot point occurred on April 17, when masks were first required, and the caseload started to decline. 

Similarly, their comparison of new infections in NYC compared to the US as a whole (minus the NYC cases) shows that corona cases declined steeply after the April 17 mandated face covering, while new cases remained high during that time throughout the United States. 

Why would masks have such a dramatic effect?

Back in March, experts thought that the virus is communicated by droplets that we expel when we cough or sneeze.  These droplets are pulled down by gravity, so are usually found within 3 feet of a sick person, so we were advised to stay away from an obviously sick person and to wash our hands and keep them away from our face to avoid transferring a virus-containing droplet to our mouth, nose or eyes.  Masks were recommended only for the sick person themselves, to prevent their expelled droplets from contaminating others (WHO, April 6).

But later in April, scientists learned that there’s another way that virus can be expelled, in the form of much smaller particles, called aerosols, especially by people talking loudly or singing. 

You can visualize the difference by spraying a window cleaner and an air freshener on a mirror.  The window cleaner forms small droplets that soon start rolling down, attracted by gravity.  The air freshener forms an aerosol of tiny drops that remain where they fell on the mirror.  In fact, we spray air freshener into the air knowing that these miniscule particles – and their pleasant odor – will remain suspended in the air for quite some time.

The realization that viral particles were found in aerosols convinced the experts that the virus could be inhaled by someone who was more than 3 feet from an infected patient, or even in a room where an infected person had previously exhaled, and this led to expansion of the advice to wear masks: 

•   The knowingly infected should wear masks to avoid spreading their droplets and aerosols, which can contain virus. 
•   The unknowingly infected (that is, presymptomatic, when viral expulsion seems highest) should similarly wear masks to avoid spreading the virus. 
•   The healthy uninfected should wear masks to avoid inhaling the aerosols of the two previous groups. 

They conclude that “wearing of face masks in public corresponds to the most effective means to prevent interhuman transmission, and this inexpensive practice, in conjunction with extensive testing, quarantine, and contact tracking, poses the most probably fighting opportunity to stop the COVID-19 pandemic, prior to the development of a vaccine.”

My comment:
Finding that the number of cases in NYC began to decrease around the same time as mask wearing was required is not sufficient to conclude that mask wearing was responsible for the decrease.  Did people actually obey the mask-wearing regulation?  Were there other events that occurred around that time that contributed to the decline in new infections?  This paper provides evidence that mask-wearing is important, but it's weak evidence, and the argument could be strengthened by other research.
You rock. Seriously.
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Offline biobook

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Re: Masks
« Reply #64 on: June 14, 2020, 07:15:31 PM »
 ;D  <takes a bow>

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Re: Masks
« Reply #65 on: June 14, 2020, 07:25:51 PM »
My comment:
Finding that the number of cases in NYC began to decrease around the same time as mask wearing was required is not sufficient to conclude that mask wearing was responsible for the decrease.  Did people actually obey the mask-wearing regulation?  Were there other events that occurred around that time that contributed to the decline in new infections?  This paper provides evidence that mask-wearing is important, but it's weak evidence, and the argument could be strengthened by other research.

Excellent comment. If I may, I'd like to offer an abbreviated version: Correlation does not prove causation!

(Side note: I almost puked several times hearing Cuomo's arrogant causation claims today, coupled with his muscle flexing.)
I've been waiting over 5 years with bated breath for someone to say that!
-- Dan

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Re: Masks
« Reply #66 on: June 14, 2020, 07:45:44 PM »
Excellent comment. If I may, I'd like to offer an abbreviated version: Correlation does not prove causation!

(Side note: I almost puked several times hearing Cuomo's arrogant causation claims today, coupled with his muscle flexing.)

Right!  But correlation does not disprove causation either.  It's just a hint, needs to be followed up.

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Re: Masks
« Reply #67 on: June 14, 2020, 07:50:27 PM »
What this does suggest, if proven, as many have suggested for other reasons as well:

the viable route forward is more masks less lockdowns. overall less pain to the economy and even the individual living their lives.

or as another article put it, if we evaluate the various measures as ROI closing businesses may be high cost/low return, closing schools may be high return but high cost and universal masking/sanitizing along with closing major events (1000s of people) are our most low cost/high return.

the emerging evidence on airborne vs touching etc. only confirms this

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Re: Masks
« Reply #68 on: June 14, 2020, 09:30:19 PM »
My comment:
Finding that the number of cases in NYC began to decrease around the same time as mask wearing was required is not sufficient to conclude that mask wearing was responsible for the decrease.  Did people actually obey the mask-wearing regulation?  Were there other events that occurred around that time that contributed to the decline in new infections?  This paper provides evidence that mask-wearing is important, but it's weak evidence, and the argument could be strengthened by other research.
Good point (and nice summary BTW)

In NY mask compliance in subways and on the street was never great (i'm not in NY but commenting based on the news reports at the time). In NJ they never required masks other than in stores. Is there evidence that they took longer to bend the curve?
The states that still had cases rising were most likely to lax lockdowns in general not because of masks specifically.
China may have stopped the spread quicker because they did a much stricter lockdown then we did.

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Re: Masks
« Reply #69 on: June 14, 2020, 10:05:26 PM »
Well, Dan asked for a summary of the article that @aygart posted, but it's disappeared.  And while I wrote a summary, this (better) summary with pictures has been published, but I'll paste mine anyway. Is this too long?

https://www.forbes.com/sites/alicegwalton/2020/06/13/face-masks-may-be-the-key-determinant-of-the-covid-19-curve-study-suggests/#44ac7f116497

Identifying airborne transmission as the dominant route for the spread of COVID-19, by Renyi Zhang and others, PNAS, published June 11, 2020

Short summary: Why did COVID-19 stop spreading so much faster in China than in Italy and the US?  And why did new cases plateau so much earlier in NYC than in the rest of the United States?  In both cases, the authors conclude that the onset of mandated face coverings made the difference, preventing tens of thousands of infections. 

Longer summary:
In China, the early response to the outbreak was SD, masks, extensive testing, and contact tracing, all put into effect simultaneously.  In China, the number of new cases increased for about 3 weeks after the lockdown, and had reached a plateau about a week after that. 

In NYC and Italy, the early response was hand washing, SD, stay-at-home, but masks were not required until a month had passed.  In these places, the number of new cases increased rapidly for about 4 weeks after the early SD requirement, and began to decrease only later, after the face covering requirement was implemented.

In the rest of the US the early response was hand washing, SD, stay-at-home and masks were not required, and the number of new cases were continuing to rise steeply (at the time they looked, May 9). 

The timing of these events suggests that mask-wearing was critical in decreasing the spread of coronavirus, quickly in China and after a delay in NYC.

A second piece of evidence they bring is from plotting the total cases in NYC, using a statistical technique called linear regression.  Their graph shows that if the original policy (SD, stay at home) had continued, the number of cases would have been much higher than it actually was.  The pivot point occurred on April 17, when masks were first required, and the caseload started to decline. 

Similarly, their comparison of new infections in NYC compared to the US as a whole (minus the NYC cases) shows that corona cases declined steeply after the April 17 mandated face covering, while new cases remained high during that time throughout the United States. 

Why would masks have such a dramatic effect?

Back in March, experts thought that the virus is communicated by droplets that we expel when we cough or sneeze.  These droplets are pulled down by gravity, so are usually found within 3 feet of a sick person, so we were advised to stay away from an obviously sick person and to wash our hands and keep them away from our face to avoid transferring a virus-containing droplet to our mouth, nose or eyes.  Masks were recommended only for the sick person themselves, to prevent their expelled droplets from contaminating others (WHO, April 6).

But later in April, scientists learned that there’s another way that virus can be expelled, in the form of much smaller particles, called aerosols, especially by people talking loudly or singing. 

You can visualize the difference by spraying a window cleaner and an air freshener on a mirror.  The window cleaner forms small droplets that soon start rolling down, attracted by gravity.  The air freshener forms an aerosol of tiny drops that remain where they fell on the mirror.  In fact, we spray air freshener into the air knowing that these miniscule particles – and their pleasant odor – will remain suspended in the air for quite some time.

The realization that viral particles were found in aerosols convinced the experts that the virus could be inhaled by someone who was more than 3 feet from an infected patient, or even in a room where an infected person had previously exhaled, and this led to expansion of the advice to wear masks: 

•   The knowingly infected should wear masks to avoid spreading their droplets and aerosols, which can contain virus. 
•   The unknowingly infected (that is, presymptomatic, when viral expulsion seems highest) should similarly wear masks to avoid spreading the virus. 
•   The healthy uninfected should wear masks to avoid inhaling the aerosols of the two previous groups. 

They conclude that “wearing of face masks in public corresponds to the most effective means to prevent interhuman transmission, and this inexpensive practice, in conjunction with extensive testing, quarantine, and contact tracking, poses the most probably fighting opportunity to stop the COVID-19 pandemic, prior to the development of a vaccine.”

My comment:
Finding that the number of cases in NYC began to decrease around the same time as mask wearing was required is not sufficient to conclude that mask wearing was responsible for the decrease.  Did people actually obey the mask-wearing regulation?  Were there other events that occurred around that time that contributed to the decline in new infections?  This paper provides evidence that mask-wearing is important, but it's weak evidence, and the argument could be strengthened by other research.
Looking at graph A in this image from the article, I would conclude that the number of cases increased for 3 weeks after the stay at home order before starting to descend and continuing to descend for many weeks after with the face mask requirement having no effect. Including the 3 weeks of increase as part of the downward trend is a scam.
I wonder what people who type "u" instead of "you" do with all their free time.

Offline biobook

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Re: Masks
« Reply #70 on: June 15, 2020, 11:13:58 AM »
Looking at graph A in this image from the article, I would conclude that the number of cases increased for 3 weeks after the stay at home order before starting to descend and continuing to descend for many weeks after with the face mask requirement having no effect. Including the 3 weeks of increase as part of the downward trend is a scam.
@avromie7 If you're saying what I think you're saying, then I agree with you 100%. 

These scientists asked "Do case numbers change after masks were required?" so they drew two dotted lines, one that best fit their data before masks - when cases were only slightly declining - and one line after masks - which show a more dramatic decrease in cases.  (first graph A)

But you come and say "Hey, wait a minute, guys!  There's another way to analyze this!  Instead of starting with the assumption that masks make a difference, just take a look at your data!" and you would draw two lines that show that cases increased for a few weeks until April 12, and then started to decline before masks were required! 

I would add: If masks made the critical difference, then new infections should have decreased immediately, but new cases wouldn't have been reported until several days later when symptoms appear.  So we would have expected the decline in reported new cases to begin a week after face covering began, not immediately.

So all of this is why it should be considered only "weak evidence", which is consistent with the importance of masking.  We'd have a much more convincing argument if it had been decreed that masks had to be worn in Italy but were forbidden in the US, and then we would have had a clearer case for concluding whether or not masks were important.  But obviously we can't do that kind of experiment, and are stuck with the data we have.  As more data analysis is added, we'll get better conclusions, rather than relying on just this paper.

The only part of your comment that I disagree with is calling this "a scam", which implies intentional fraud. The Forbes journalist wasn't as astute as you, and didn't notice the problem with their analysis, but experts in epidemiology surely would have.  (Note that the scientists who did this were actually chemists.)  This is the kind of dispute that always happens as scientists try to reach agreement, and the conflict is usually resolved when additional data either supports or refutes it. 

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Re: Masks
« Reply #71 on: June 15, 2020, 12:37:15 PM »
I would think that cases would take a while (more than a week, likely 2 or 3) to start going down after the correct procedures were put in place. We have to remember that people only would get tested after a couple of days with symptoms and the results come back a few days later. Also family members would likely get it if they stayed at home with a sick person as no one was socially distancing or wearing masks around family members unless they had symptoms which was usually to late to stop transmission between family members. This suports the theory that stay at home orders is what really slowed it down.

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Re: Masks
« Reply #72 on: June 15, 2020, 01:27:04 PM »
The only part of your comment that I disagree with is calling this "a scam", which implies intentional fraud. The Forbes journalist wasn't as astute as you, and didn't notice the problem with their analysis, but experts in epidemiology surely would have.  (Note that the scientists who did this were actually chemists.)  This is the kind of dispute that always happens as scientists try to reach agreement, and the conflict is usually resolved when additional data either supports or refutes it. 
I don't know who deserves the blame and who should be given the benefit of the doubt that they're just "passing on" the information they received, but someone published something that is fatally flawed to the point that a layman like me glancing thru the article says something doesn't make sense. I can compare the week before the mask requirement to the weeks after and you'll see the downward trend slowed when masks were required.
I would think that cases would take a while (more than a week, likely 2 or 3) to start going down after the correct procedures were put in place. We have to remember that people only would get tested after a couple of days with symptoms and the results come back a few days later. Also family members would likely get it if they stayed at home with a sick person as no one was socially distancing or wearing masks around family members unless they had symptoms which was usually to late to stop transmission between family members. This suports the theory that stay at home orders is what really slowed it down.
Alternatively, it has nothing to do with the stay at home order, rather when people decided to stay home (which actually happened a few days before the stay at home order) and there was no need for government involvement.
I wonder what people who type "u" instead of "you" do with all their free time.

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Re: Masks
« Reply #73 on: June 16, 2020, 12:05:40 AM »
I would think that cases would take a while (more than a week, likely 2 or 3) to start going down after the correct procedures were put in place. We have to remember that people only would get tested after a couple of days with symptoms and the results come back a few days later. Also family members would likely get it if they stayed at home with a sick person as no one was socially distancing or wearing masks around family members unless they had symptoms which was usually to late to stop transmission between family members. This suports the theory that stay at home orders is what really slowed it down.
Stay-at-home occurred in NYC and rest of the country, and the flattening of the curve is seen in both (A and B in the graph avromie7 posted) but mask-wearing had only been implemented in NY, and the steep decline is shown only in NYC (A, not B).  It is difficult to disentangle how much each contributed, just from looking at these graphs.

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Re: Masks
« Reply #74 on: June 16, 2020, 12:19:50 AM »
I don't know who deserves the blame and who should be given the benefit of the doubt that they're just "passing on" the information they received, but someone published something that is fatally flawed to the point that a layman like me glancing thru the article says something doesn't make sense.
It's not fatally flawed.  The authors interpreted it one way, and you (admirably) found another way to interpret it.  You should always be reading this way, asking "what did you base your conclusions on?" and "is there another interpretation for your data?"

Quote
Alternatively, it has nothing to do with the stay at home order, rather when people decided to stay home (which actually happened a few days before the stay at home order) and there was no need for government involvement.
It's true that another problem with this study is that they don't know how people behaved -did they actually stay home when the government required it, did they wear masks, etc.
 
There was no need for the government to tell me to stay home, and no need to tell you to stay home.   But you know that fool who lives on the next block over...?  I'm glad the government told him to stay home.

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Re: Masks
« Reply #75 on: June 16, 2020, 12:23:42 AM »
It's not fatally flawed.  The authors interpreted it one way, and you (admirably) found another way to interpret it.  You should always be reading this way, asking "what did you base your conclusions on?" and "is there another interpretation for your data?"
It's true that another problem with this study is that they don't know how people behaved -did they actually stay home when the government required it, did they wear masks, etc.
 
There was no need for the government to tell me to stay home, and no need to tell you to stay home.   But you know that fool who lives on the next block over...?  I'm glad the government told him to stay home.
Sadly many of the fools down the block did not listen and many who stayed home on their own are still not going out.
Based entirely on what I am seeing in my community, it seems people made their own decisions and stuck with them nothing to do with govt regulations.
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Re: Masks
« Reply #76 on: June 16, 2020, 08:33:22 AM »
Stay-at-home occurred in NYC and rest of the country, and the flattening of the curve is seen in both (A and B in the graph avromie7 posted) but mask-wearing had only been implemented in NY, and the steep decline is shown only in NYC (A, not B).  It is difficult to disentangle how much each contributed, just from looking at these graphs.
You mean to tell me that only people in NY were wearing masks. I dont think that is true. Perhaps, the reason why it kept on going up outside of NY was because people were less cautious as it wasn't going around much there.

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Re: Masks
« Reply #77 on: June 16, 2020, 08:44:23 AM »
Sadly many of the fools down the block did not listen and many who stayed home on their own are still not going out.
Based entirely on what I am seeing in my community, it seems people made their own decisions and stuck with them nothing to do with govt regulations.
You obviously live in a community very different than mine. In my community almost no schools closed until they were forced to by the government, barely anyone wore masks in stores until they were mandated, few even heard of the concept of social distancing until it was required, etc.
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Offline yuneeq

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Re: Masks
« Reply #78 on: June 17, 2020, 08:58:56 AM »
Well, Dan asked for a summary of the article that @aygart posted, but it's disappeared.  And while I wrote a summary, this (better) summary with pictures has been published, but I'll paste mine anyway. Is this too long?

https://www.forbes.com/sites/alicegwalton/2020/06/13/face-masks-may-be-the-key-determinant-of-the-covid-19-curve-study-suggests/#44ac7f116497

Identifying airborne transmission as the dominant route for the spread of COVID-19, by Renyi Zhang and others, PNAS, published June 11, 2020

Short summary: Why did COVID-19 stop spreading so much faster in China than in Italy and the US?  And why did new cases plateau so much earlier in NYC than in the rest of the United States?  In both cases, the authors conclude that the onset of mandated face coverings made the difference, preventing tens of thousands of infections. 

Longer summary:
In China, the early response to the outbreak was SD, masks, extensive testing, and contact tracing, all put into effect simultaneously.  In China, the number of new cases increased for about 3 weeks after the lockdown, and had reached a plateau about a week after that. 

In NYC and Italy, the early response was hand washing, SD, stay-at-home, but masks were not required until a month had passed.  In these places, the number of new cases increased rapidly for about 4 weeks after the early SD requirement, and began to decrease only later, after the face covering requirement was implemented.

In the rest of the US the early response was hand washing, SD, stay-at-home and masks were not required, and the number of new cases were continuing to rise steeply (at the time they looked, May 9). 

The timing of these events suggests that mask-wearing was critical in decreasing the spread of coronavirus, quickly in China and after a delay in NYC.

A second piece of evidence they bring is from plotting the total cases in NYC, using a statistical technique called linear regression.  Their graph shows that if the original policy (SD, stay at home) had continued, the number of cases would have been much higher than it actually was.  The pivot point occurred on April 17, when masks were first required, and the caseload started to decline. 

Similarly, their comparison of new infections in NYC compared to the US as a whole (minus the NYC cases) shows that corona cases declined steeply after the April 17 mandated face covering, while new cases remained high during that time throughout the United States. 

Why would masks have such a dramatic effect?

Back in March, experts thought that the virus is communicated by droplets that we expel when we cough or sneeze.  These droplets are pulled down by gravity, so are usually found within 3 feet of a sick person, so we were advised to stay away from an obviously sick person and to wash our hands and keep them away from our face to avoid transferring a virus-containing droplet to our mouth, nose or eyes.  Masks were recommended only for the sick person themselves, to prevent their expelled droplets from contaminating others (WHO, April 6).

But later in April, scientists learned that there’s another way that virus can be expelled, in the form of much smaller particles, called aerosols, especially by people talking loudly or singing. 

You can visualize the difference by spraying a window cleaner and an air freshener on a mirror.  The window cleaner forms small droplets that soon start rolling down, attracted by gravity.  The air freshener forms an aerosol of tiny drops that remain where they fell on the mirror.  In fact, we spray air freshener into the air knowing that these miniscule particles – and their pleasant odor – will remain suspended in the air for quite some time.

The realization that viral particles were found in aerosols convinced the experts that the virus could be inhaled by someone who was more than 3 feet from an infected patient, or even in a room where an infected person had previously exhaled, and this led to expansion of the advice to wear masks: 

•   The knowingly infected should wear masks to avoid spreading their droplets and aerosols, which can contain virus. 
•   The unknowingly infected (that is, presymptomatic, when viral expulsion seems highest) should similarly wear masks to avoid spreading the virus. 
•   The healthy uninfected should wear masks to avoid inhaling the aerosols of the two previous groups. 

They conclude that “wearing of face masks in public corresponds to the most effective means to prevent interhuman transmission, and this inexpensive practice, in conjunction with extensive testing, quarantine, and contact tracking, poses the most probably fighting opportunity to stop the COVID-19 pandemic, prior to the development of a vaccine.”

My comment:
Finding that the number of cases in NYC began to decrease around the same time as mask wearing was required is not sufficient to conclude that mask wearing was responsible for the decrease.  Did people actually obey the mask-wearing regulation?  Were there other events that occurred around that time that contributed to the decline in new infections?  This paper provides evidence that mask-wearing is important, but it's weak evidence, and the argument could be strengthened by other research.

So much fake news in this “research” even if I want to agree with the premise.

Masks were never required in NYC. Aerosolized spread was known from February, not April. Couldn’t read further.

Edit- Apparently mask coverings were mandated in NY but not in all situations. My mistake.
« Last Edit: June 17, 2020, 09:03:11 AM by yuneeq »
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Offline biobook

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Re: Masks
« Reply #79 on: June 17, 2020, 02:47:51 PM »
Masks were never required in NYC. 

Edit- Apparently mask coverings were mandated in NY but not in all situations. My mistake.
Yes, at least according to the article, "All New Yorkers were mandated to use face covering in public starting on April 17, when social distancing was not possible."

Aerosolized spread was known from February, not April.
Again, from the article: "Recent experimental studies have examined the stability of SARS-CoV-2, showing that the virus remains infectious in aerosols for hours (12)"  Reference (12) was published in the April 16 issue of NEJM, though online March 17.

So much fake news in this “research” even if I want to agree with the premise.
...   Couldn’t read further.
I would call it "weak evidence" (and did, in the last line). "Fake news" seems to imply deliberate misinformation, which was not my intention, and probably not the authors' either.