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Masks are effective at stopping people from unintentionally infecting others. See: https://www.nytimes.com/2020/04/10/well/live/coronavirus-face-masks-guides-p

by Mr_P 6y ago

Masks are effective at stopping people from unintentionally infecting others. See: https://www.nytimes.com/2020/04/10/well/live/coronavirus-face-masks-guides-protection-personal-protective-equipment.html https://www.nytimes.com/2020/04/10/well/live/coronavirus-fac... "Even a simple mask is very effective at trapping droplets from your coughs and sneezes. A recent study published in Nature from the University of Hong Kong and the University of Maryland asked 111 people, infected with various viral illnesses (influenza, rhinovirus and a more-mild coronavirus), to exhale into a giant funnel. Sometimes their noses and mouths weren’t covered; other times they used a simple, not-particularly-well-fitted mask. Without the masks, the infected people exhaled contagious droplets and aerosols, tiny particles that linger in the air, about 30 percent of the time they were tested. When the infected patients wore a mask, it blocked nearly 100 percent of viral droplets and some of the aerosol particles."

partiallypro 6y ago
The person you are replying to is talking specifically about Influenza which isn't spread as widely through droplets, while COVID-19 is spread this way almost exclusively.
- Mr_P 6y ago
  "Most experts think that flu viruses spread mainly by droplets..." (https://www.cdc.gov/flu/about/disease/spread.htm https://www.cdc.gov/flu/about/disease/spread.htm)
  - partiallypro 6y ago
    Mainly /= exclusively. COVID as far as we know are spread exclusively through droplets. Influenza can be aerosolized https://www.cdc.gov/niosh/topics/flu/transmission.html https://www.cdc.gov/niosh/topics/flu/transmission.html
DanBC 6y ago
But see this research, which found masks didn't help prevent covid-19 from leaving infected people. https://annals.org/aim/fullarticle/2764367/effectiveness-surgical-cotton-masks-blocking-sars-cov-2-controlled-comparison https://annals.org/aim/fullarticle/2764367/effectiveness-sur... If people are going to wear masks we need to make sure that they don't touch the mask or their face, or that they wash their hands immediately after doing so.
- erik 6y ago
  Interesting, they state the conclusion that "both surgical and cotton masks seem to be ineffective in preventing the dissemination of SARS–CoV-2 from the coughs of patients with COVID-19 to the environment" But they also say this: "The median viral loads after coughs without a mask, with a surgical mask, and with a cotton mask were 2.56 log copies/mL, 2.42 log copies/mL, and 1.85 log copies/mL, respectively." That seems like a significant reduction in transmitted viral load? I would think that masks can have a positive impact even if they aren't perfect filters. If you look at their table of data, the reduction trend is consistent across their tests. But between the small number of patients(4) and samples, and the number of Petri dishes that came back as 'Not Detected', it seems like a pretty low powered study. :-/ They are also explicitly testing coughs. I wonder about the effects on filtering droplets generated from normal breathing and talking.
  - belorn 6y ago
    > I would think that masks can have a positive impact even if they aren't perfect filters. That is when behavior comes in. If people are more likely to ignore social distancing if they wear a mask then you might get the opposite effect, as social distancing is seen as better protective measure than masks. This is one of the reasons why the health department in my nation only recommend masks for risk groups, like if you are working with elderly people.
    - em500 6y ago
      This is a completely speculative conjecture known as risk compensation (https://en.wikipedia.org/wiki/Risk_compensation https://en.wikipedia.org/wiki/Risk_compensation). It's often brought up in opposition of mandatory safety measures (quite prominently around seat belt legislation in the 1970s), but AFAIK it's never been shown to be numerically significant.
bcoates 6y ago
But in 1918 they were using specifically gauze, presumably because it's easier to breathe through, or maybe just because it seems medical-y. The study in the NYT article is using non-woven paper masks, which act a decent barrier to ballistic particles. Gauze would be way less effective than even loose woven fabric at stoping the 5um particles they're measuring. Like the paper masks, it would be completely ineffective at stopping the influenza-carrying aerosols. "nearly 100%" is a pretty big misstatement of the study as well, while it showed a statistically significant difference between the groups, so much of the no-mask control group recorded 0 virus load from droplets that the size of the effect can't be meaningfully quantified

by Mr_P 6y ago

partiallypro 6y ago

The person you are replying to is talking specifically about Influenza which isn't spread as widely through droplets, while COVID-19 is spread this way almost exclusively.

Mr_P 6y ago
"Most experts think that flu viruses spread mainly by droplets..." (https://www.cdc.gov/flu/about/disease/spread.htm https://www.cdc.gov/flu/about/disease/spread.htm)
- partiallypro 6y ago
  Mainly /= exclusively. COVID as far as we know are spread exclusively through droplets. Influenza can be aerosolized https://www.cdc.gov/niosh/topics/flu/transmission.html https://www.cdc.gov/niosh/topics/flu/transmission.html

DanBC 6y ago

But see this research, which found masks didn't help prevent covid-19 from leaving infected people. https://annals.org/aim/fullarticle/2764367/effectiveness-surgical-cotton-masks-blocking-sars-cov-2-controlled-comparison https://annals.org/aim/fullarticle/2764367/effectiveness-sur... If people are going to wear masks we need to make sure that they don't touch the mask or their face, or that they wash their hands immediately after doing so.

erik 6y ago
Interesting, they state the conclusion that "both surgical and cotton masks seem to be ineffective in preventing the dissemination of SARS–CoV-2 from the coughs of patients with COVID-19 to the environment" But they also say this: "The median viral loads after coughs without a mask, with a surgical mask, and with a cotton mask were 2.56 log copies/mL, 2.42 log copies/mL, and 1.85 log copies/mL, respectively." That seems like a significant reduction in transmitted viral load? I would think that masks can have a positive impact even if they aren't perfect filters. If you look at their table of data, the reduction trend is consistent across their tests. But between the small number of patients(4) and samples, and the number of Petri dishes that came back as 'Not Detected', it seems like a pretty low powered study. :-/ They are also explicitly testing coughs. I wonder about the effects on filtering droplets generated from normal breathing and talking.
- belorn 6y ago
  > I would think that masks can have a positive impact even if they aren't perfect filters. That is when behavior comes in. If people are more likely to ignore social distancing if they wear a mask then you might get the opposite effect, as social distancing is seen as better protective measure than masks. This is one of the reasons why the health department in my nation only recommend masks for risk groups, like if you are working with elderly people.
  - em500 6y ago
    This is a completely speculative conjecture known as risk compensation (https://en.wikipedia.org/wiki/Risk_compensation https://en.wikipedia.org/wiki/Risk_compensation). It's often brought up in opposition of mandatory safety measures (quite prominently around seat belt legislation in the 1970s), but AFAIK it's never been shown to be numerically significant.

bcoates 6y ago

But in 1918 they were using specifically gauze, presumably because it's easier to breathe through, or maybe just because it seems medical-y. The study in the NYT article is using non-woven paper masks, which act a decent barrier to ballistic particles. Gauze would be way less effective than even loose woven fabric at stoping the 5um particles they're measuring. Like the paper masks, it would be completely ineffective at stopping the influenza-carrying aerosols. "nearly 100%" is a pretty big misstatement of the study as well, while it showed a statistically significant difference between the groups, so much of the no-mask control group recorded 0 virus load from droplets that the size of the effect can't be meaningfully quantified