3 ms·

That's actually the opposite of what the evidence shows. Masks - even crappy ones, with poor mask protocol - dramatically cut infections https://arstechnica.co

That's actually the opposite of what the evidence shows. Masks - even crappy ones, with poor mask protocol - dramatically cut infections https://arstechnica.com/science/2020/06/modeling-the-impact-of-face-masks-on-the-covid-19-pandemic/ https://arstechnica.com/science/2020/06/modeling-the-impact-... Citation: https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818 https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818 Remember: even if a mask doesn't effectively filter out very small particles, it still restricts the velocity of air passing through it. This means aerosolized particles will not travel as far.

DanBC 6y ago
About your arstechnica link: if masks don't work all that effectively you need huge numbers of people to wear them to prevent a single infection. https://www.fhi.no/globalassets/dokumenterfiler/rapporter/2020/should-individuals-in-the-community-without-respiratory-symptoms-wear-facemasks-to-reduce-the-spread-of-covid-19-report-2020.pdf https://www.fhi.no/globalassets/dokumenterfiler/rapporter/20... > Non-medical facemasks include a variety of products. There is no reliable evidence of the effectiveness of non-medical facemasks in community settings. There is likely to be substantial variation in effectiveness between products. However, there is only limited evidence from laboratory studies of potential differences in effectiveness when different products are used in the community. > Given the low prevalence of COVID-19 currently, even if facemasks are assumed to be effective, the difference in infection rates between using facemasks and not using facemasks would be small.Assuming that 20% of people infectious with SARS-CoV-2 do not have symptoms,and assuming a risk reduction of 40% for wearing facemask, 200000 people would need to wear facemasks to prevent one new infection per week in the current epide-miological situation. Here's all the science: we don't know if masks work or not. https://www.cebm.net/covid-19/masking-lack-of-evidence-with-politics/ https://www.cebm.net/covid-19/masking-lack-of-evidence-with-... They have a plausible mechanism of action, but they also have plausible mechanisms of harm. The above link includes one trial where they appeared to be harmful: > It is debatable whether any of these results could be applied to the transmission of SARs-CoV-2. Only one randomised trial (n=569) included cloth masks. This trial found ILI rates were 13 times higher in Vietnamese hospital workers allocated to cloth masks compared to medical/surgical masks, RR 13.25, (95%CI 1.74 to 100.97) and over three times higher when compared to no masks,* RR 3.49 (95%CI 1.00 to 12.17). 4 This is potentially because the masks start to lose effectiveness as soon as you put them on. DIY cloth masks soon become waterlogged with condensation, and then when you breath you push out aerosolised drops. https://www.ijic.info/article/view/10788 https://www.ijic.info/article/view/10788 > This study was conducted to check the efficacy of face masks in limiting bacterial dispersal when worn continuously in Operation Theater. A comparison was done to find out difference between fabric and two ply disposable masks. The first sample was collected prior to wearing the mask, using cough plate method holding a blood agar plate approximately 10 -12 centimeters away from the mouth. the personnel were asked to produce “ahh” phonation. Participants were then asked to don the face mask, continue routine work and report to the study center located inside the theater for further sample collections at designated intervals of 30, 60, 90, 120 and 150 minutes after wearing the fabric mask made of cotton. the study was replicated on immediate next day using two ply disposable mask keeping all the other conditions and personnel exactly the same. Bacterial counts before wearing the mask were 5.36±4.38 and 5.7±2.99 on day 1 and day 2 of study. Bacterial counts were 0.96±1.06 (P<0.001) and 0.7±0.87 (P<0.001) at 30 min; 2.33±1.42 (P<0.001) and 2.36±1.03 (P<0.001) at 60 min; 3.23±1.54 (P=0.007) and 4.16±1.78 (P=0.011) at 90 min; 5.63±4.02 (P=0.67) and 4.9±1.98 (P=0.161) at 120 min and 7.03±4.45 (P=0.019) and 5.6±2.21 (P=0.951) at 150min respectively for fabric and two ply disposable mask. Counts were near pre-wear level in about two hours irrespective of the type of mask. There was no significant difference between cotton fabric and two ply disposable masks. Face masks significantly decreased bacterial dispersal initially but became almost ineffective after two hours of use. My point is that we don't have the evidence to say whether masks work or not. You posting links to arstechnica and un-peer-reviewed pre-prints supports my point, doesn't it? If we had a Cochrane Collaboration meta analysis saying masks worked everyone would be posting that.
- CogentHedgehog 6y ago
  > There is no reliable evidence of the effectiveness of non-medical facemasks in community settings. There has been only very limited study of non-medical (cloth) masks so far, because there was not a prior crisis that NEEDED them (where surgical mask supplies were insufficient). The fundamental problem with most of your points is that lack of research on effectiveness is NOT the same thing as proof of ineffectiveness. We can assume that most cloth masks are probably not AS effective as surgical masks or N95 masks (although some materials can achieve surprisingly good filtration), but that's not the same thing as saying they're useless either. Especially true for models with good fit and the ability to install filters. But even a modest reduction in R-effective can greatly reduce the number of number of people infected over time. The healthaffairs article shows that mask mandates reduced transmission: https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818 https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818 Beyond that, I'm not going to waste time going point by point in debate with someone determined to "disprove" guidance from the best available medical authorities.

DanBC 6y ago

About your arstechnica link: if masks don't work all that effectively you need huge numbers of people to wear them to prevent a single infection. https://www.fhi.no/globalassets/dokumenterfiler/rapporter/2020/should-individuals-in-the-community-without-respiratory-symptoms-wear-facemasks-to-reduce-the-spread-of-covid-19-report-2020.pdf https://www.fhi.no/globalassets/dokumenterfiler/rapporter/20... > Non-medical facemasks include a variety of products. There is no reliable evidence of the effectiveness of non-medical facemasks in community settings. There is likely to be substantial variation in effectiveness between products. However, there is only limited evidence from laboratory studies of potential differences in effectiveness when different products are used in the community. > Given the low prevalence of COVID-19 currently, even if facemasks are assumed to be effective, the difference in infection rates between using facemasks and not using facemasks would be small.Assuming that 20% of people infectious with SARS-CoV-2 do not have symptoms,and assuming a risk reduction of 40% for wearing facemask, 200000 people would need to wear facemasks to prevent one new infection per week in the current epide-miological situation. Here's all the science: we don't know if masks work or not. https://www.cebm.net/covid-19/masking-lack-of-evidence-with-politics/ https://www.cebm.net/covid-19/masking-lack-of-evidence-with-... They have a plausible mechanism of action, but they also have plausible mechanisms of harm. The above link includes one trial where they appeared to be harmful: > It is debatable whether any of these results could be applied to the transmission of SARs-CoV-2. Only one randomised trial (n=569) included cloth masks. This trial found ILI rates were 13 times higher in Vietnamese hospital workers allocated to cloth masks compared to medical/surgical masks, RR 13.25, (95%CI 1.74 to 100.97) and over three times higher when compared to no masks,* RR 3.49 (95%CI 1.00 to 12.17). 4 This is potentially because the masks start to lose effectiveness as soon as you put them on. DIY cloth masks soon become waterlogged with condensation, and then when you breath you push out aerosolised drops. https://www.ijic.info/article/view/10788 https://www.ijic.info/article/view/10788 > This study was conducted to check the efficacy of face masks in limiting bacterial dispersal when worn continuously in Operation Theater. A comparison was done to find out difference between fabric and two ply disposable masks. The first sample was collected prior to wearing the mask, using cough plate method holding a blood agar plate approximately 10 -12 centimeters away from the mouth. the personnel were asked to produce “ahh” phonation. Participants were then asked to don the face mask, continue routine work and report to the study center located inside the theater for further sample collections at designated intervals of 30, 60, 90, 120 and 150 minutes after wearing the fabric mask made of cotton. the study was replicated on immediate next day using two ply disposable mask keeping all the other conditions and personnel exactly the same. Bacterial counts before wearing the mask were 5.36±4.38 and 5.7±2.99 on day 1 and day 2 of study. Bacterial counts were 0.96±1.06 (P<0.001) and 0.7±0.87 (P<0.001) at 30 min; 2.33±1.42 (P<0.001) and 2.36±1.03 (P<0.001) at 60 min; 3.23±1.54 (P=0.007) and 4.16±1.78 (P=0.011) at 90 min; 5.63±4.02 (P=0.67) and 4.9±1.98 (P=0.161) at 120 min and 7.03±4.45 (P=0.019) and 5.6±2.21 (P=0.951) at 150min respectively for fabric and two ply disposable mask. Counts were near pre-wear level in about two hours irrespective of the type of mask. There was no significant difference between cotton fabric and two ply disposable masks. Face masks significantly decreased bacterial dispersal initially but became almost ineffective after two hours of use. My point is that we don't have the evidence to say whether masks work or not. You posting links to arstechnica and un-peer-reviewed pre-prints supports my point, doesn't it? If we had a Cochrane Collaboration meta analysis saying masks worked everyone would be posting that.

CogentHedgehog 6y ago
> There is no reliable evidence of the effectiveness of non-medical facemasks in community settings. There has been only very limited study of non-medical (cloth) masks so far, because there was not a prior crisis that NEEDED them (where surgical mask supplies were insufficient). The fundamental problem with most of your points is that lack of research on effectiveness is NOT the same thing as proof of ineffectiveness. We can assume that most cloth masks are probably not AS effective as surgical masks or N95 masks (although some materials can achieve surprisingly good filtration), but that's not the same thing as saying they're useless either. Especially true for models with good fit and the ability to install filters. But even a modest reduction in R-effective can greatly reduce the number of number of people infected over time. The healthaffairs article shows that mask mandates reduced transmission: https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818 https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818 Beyond that, I'm not going to waste time going point by point in debate with someone determined to "disprove" guidance from the best available medical authorities.