3 ms·

> It says that cloth masks are 70% effective, and then exaggerates this to say that cloth masks are "not effective." No. It says that the main South Korean stu

by bambax 7y ago

> It says that cloth masks are 70% effective, and then exaggerates this to say that cloth masks are "not effective." No. It says that the main South Korean study "found" that masks were 70% effective, but that that study is not significant, because it was based on only 4 people, "one of whom could not produce detectable virus particles even without a mask" -- so really, 3 people. It also says that a much more important study [1], based on 1607 hospital workers found that penetration of cloth masks by particles was almost 97%. That other study was made in 2015, so before covid, but there is no reason to believe its results would be different with the covid virus; it's certainly not disproved by a study based on 3 people. [1] https://bmjopen.bmj.com/content/5/4/e006577 https://bmjopen.bmj.com/content/5/4/e006577

DanBC 7y ago
Also, the 4 person South Korean study was very clear in their conclusion: https://annals.org/aim/fullarticle/2764367/effectiveness-surgical-cotton-masks-blocking-sars-cov-2-controlled-comparison https://annals.org/aim/fullarticle/2764367/effectiveness-sur... > In conclusion, 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 and external mask surface.
- jtoomim 7y ago
  That study is n=4. They didn't have enough statistical power to make any conclusions of that sort. Incidentally, if you look at the SK study's actual data, it appears that the cloth and surgical masks reduced the concentration of the virus by about 0.5 to 1.0 log units -- that is, by 66% to 90%. However, those results results were not statistically significant, because n=4. Nancy Leung, from Benjamin Cowling's lab in Hong Kong, did a much better study, n=114. They found that surgical masks did confer significant protective benefits. https://www.nature.com/articles/s41591-020-0843-2.pdf https://www.nature.com/articles/s41591-020-0843-2.pdf
- jnbiche 7y ago
  First, each patient coughed directly upon a petri dish 20 cm away, not once but 5 times. I don't think anyone would rationally believe that a non-fitted mask would have a high probability of providing protection to a person directly coughed on by an infectious mask-wearer, all at a distance of 20cm. If they were going to test under those conditions, they should have used an N95 mask. Doing it with a surgical mask under such conditions was a waste of time and no surprise at all. The argument has never been that non-fitted masks prevent 100% of all viral particles emitted by an infectious person from escaping into the environment (which is what that tests, since it only takes a few virions to start a colony in a culture). The argument has been that wearing a non-fitted mask can significant decrease the amount of virus-laden droplets floating around in the air, and falling onto surfaces. The more we find out about asymptomatic carriers, the more this makes sense. These carriers aren't going around coughing their lungs out, they transmitting disease by talking and breathing. A mask likely helps a lot with that. I've really like to see the same experiment repeated, but with the patient wearing the mask and talking, and the petri disk held ~2 meters away. These are the conditions under which the disease is being transmitted now, outside of households and healthcare facilities.
a1369209993 7y ago
> a much more important study [1], based on 1607 hospital workers found that penetration of cloth masks by particles was almost 97%. Amusingly (or horrifyingly, if you prefer), I'm fairly sure that's the study that #Masks4All posts were referring to when they claimed that cloth masks are 96% effective. I recognize the 1607 number at least.

by bambax 7y ago

DanBC 7y ago

Also, the 4 person South Korean study was very clear in their conclusion: https://annals.org/aim/fullarticle/2764367/effectiveness-surgical-cotton-masks-blocking-sars-cov-2-controlled-comparison https://annals.org/aim/fullarticle/2764367/effectiveness-sur... > In conclusion, 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 and external mask surface.

jtoomim 7y ago
That study is n=4. They didn't have enough statistical power to make any conclusions of that sort. Incidentally, if you look at the SK study's actual data, it appears that the cloth and surgical masks reduced the concentration of the virus by about 0.5 to 1.0 log units -- that is, by 66% to 90%. However, those results results were not statistically significant, because n=4. Nancy Leung, from Benjamin Cowling's lab in Hong Kong, did a much better study, n=114. They found that surgical masks did confer significant protective benefits. https://www.nature.com/articles/s41591-020-0843-2.pdf https://www.nature.com/articles/s41591-020-0843-2.pdf
jnbiche 7y ago
First, each patient coughed directly upon a petri dish 20 cm away, not once but 5 times. I don't think anyone would rationally believe that a non-fitted mask would have a high probability of providing protection to a person directly coughed on by an infectious mask-wearer, all at a distance of 20cm. If they were going to test under those conditions, they should have used an N95 mask. Doing it with a surgical mask under such conditions was a waste of time and no surprise at all. The argument has never been that non-fitted masks prevent 100% of all viral particles emitted by an infectious person from escaping into the environment (which is what that tests, since it only takes a few virions to start a colony in a culture). The argument has been that wearing a non-fitted mask can significant decrease the amount of virus-laden droplets floating around in the air, and falling onto surfaces. The more we find out about asymptomatic carriers, the more this makes sense. These carriers aren't going around coughing their lungs out, they transmitting disease by talking and breathing. A mask likely helps a lot with that. I've really like to see the same experiment repeated, but with the patient wearing the mask and talking, and the petri disk held ~2 meters away. These are the conditions under which the disease is being transmitted now, outside of households and healthcare facilities.

a1369209993 7y ago

> a much more important study [1], based on 1607 hospital workers found that penetration of cloth masks by particles was almost 97%. Amusingly (or horrifyingly, if you prefer), I'm fairly sure that's the study that #Masks4All posts were referring to when they claimed that cloth masks are 96% effective. I recognize the 1607 number at least.