Alligatorob
SF VIP
I have been thinking about this for a while and after reading Squatting dog's post on another thread, copied below, began doing a bit of my own online research.
In the interest of full disclosure I have always believed masks helped and have supported mask wearing. This has been based on my background as an engineer who has studied filtration, my non-expert understanding of the Covid virus transmission process, and gut feelings. Reading Squatting dog's post and looking into his references made me decide I needed to do more research. This research has changed my mind a bit, I still think mask wearing helps, but maybe not so much as I once did.
In summary what I believe I have found is good evidence that mask wearing does help reduce transmission rates. Not as much as I had thought, but there does appear to me to be some benefit. In doing the research I tried to stick to peer reviewed epidemiological studies. I believe epidemiological studies are best as they look at actual population level transmission rates and that's what matters. The problem with epidemiological studies is that they are expensive and difficult to control. You need to look at a lot of them to gain some idea of consensus. Here are a few of the references I looked at and what they said, my research was by no means complete, lots more out there than I have been able to absorb.
The Impact of Community Masking on COVID-19: A Cluster-Randomized Trial in Bangladesh A study of 342,126 adults that found mask wearing reduced Covid by 9.3% not a huge reduction, but something.
https://www.poverty-action.org/site..._RCT____Symptomatic_Seropositivity_083121.pdf
Face masks: what the data say an article in the prominent journal Nature. After reviewing "publicly available daily county-level data of confirmed COVID-19 cases from March 25 through May 21.20 The data covered all states plus Washington, D.C., and the analytical sample included 2,930 unique counties plus New York City" that found, in part: "US states mandating the use of face masks in public had a greater decline in daily COVID-19 growth rates after issuing these mandates compared with states that did not issue mandates."
Note the "Reference period" refers to the time when the mask requirements went into effect, to the left of the red dashed like was before, to the right after.
https://www.nature.com/articles/d41586-020-02801-8 and https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818
Mask adherence and rate of COVID-19 across the United States found:
"In conclusion, we show that mask wearing adherence, regardless of mask wearing policy, may curb the spread of COVID-19 infections. We recommend renewed efforts be employed to improve adherence to mask wearing."
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0249891
A study of coronavirus mortality in 200 countries: Association of Country-wide Coronavirus Mortality with Demographics, Testing, Lockdowns, and Public Wearing of Masks
https://www.ajtmh.org/view/journals/tpmd/103/6/article-p2400.xml#container-33902-item-33911
This one is a media piece, I include it only because it provides links to a lot of good relevant peer reviewed papers:
https://www.kxan.com/news/coronavir...-scientific-studies-that-explain-why-they-do/
I also found some evidence that masks can reduce the viral dose, reducing Covid severity.
In the interest of full disclosure I have always believed masks helped and have supported mask wearing. This has been based on my background as an engineer who has studied filtration, my non-expert understanding of the Covid virus transmission process, and gut feelings. Reading Squatting dog's post and looking into his references made me decide I needed to do more research. This research has changed my mind a bit, I still think mask wearing helps, but maybe not so much as I once did.
In summary what I believe I have found is good evidence that mask wearing does help reduce transmission rates. Not as much as I had thought, but there does appear to me to be some benefit. In doing the research I tried to stick to peer reviewed epidemiological studies. I believe epidemiological studies are best as they look at actual population level transmission rates and that's what matters. The problem with epidemiological studies is that they are expensive and difficult to control. You need to look at a lot of them to gain some idea of consensus. Here are a few of the references I looked at and what they said, my research was by no means complete, lots more out there than I have been able to absorb.
The Impact of Community Masking on COVID-19: A Cluster-Randomized Trial in Bangladesh A study of 342,126 adults that found mask wearing reduced Covid by 9.3% not a huge reduction, but something.
https://www.poverty-action.org/site..._RCT____Symptomatic_Seropositivity_083121.pdf
Face masks: what the data say an article in the prominent journal Nature. After reviewing "publicly available daily county-level data of confirmed COVID-19 cases from March 25 through May 21.20 The data covered all states plus Washington, D.C., and the analytical sample included 2,930 unique counties plus New York City" that found, in part: "US states mandating the use of face masks in public had a greater decline in daily COVID-19 growth rates after issuing these mandates compared with states that did not issue mandates."
Note the "Reference period" refers to the time when the mask requirements went into effect, to the left of the red dashed like was before, to the right after.
https://www.nature.com/articles/d41586-020-02801-8 and https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818
Mask adherence and rate of COVID-19 across the United States found:
"In conclusion, we show that mask wearing adherence, regardless of mask wearing policy, may curb the spread of COVID-19 infections. We recommend renewed efforts be employed to improve adherence to mask wearing."
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0249891
A study of coronavirus mortality in 200 countries: Association of Country-wide Coronavirus Mortality with Demographics, Testing, Lockdowns, and Public Wearing of Masks
https://www.ajtmh.org/view/journals/tpmd/103/6/article-p2400.xml#container-33902-item-33911
This one is a media piece, I include it only because it provides links to a lot of good relevant peer reviewed papers:
https://www.kxan.com/news/coronavir...-scientific-studies-that-explain-why-they-do/
I also found some evidence that masks can reduce the viral dose, reducing Covid severity.
- Another Explanation for Why Cloth Masks Reduce COVID-19 Severity" https://jamanetwork.com/journals/jama/fullarticle/2777695
- Masks Do More Than Protect Others During COVID-19: Reducing the Inoculum of SARS-CoV-2 to Protect the Wearer https://link.springer.com/article/10.1007/s11606-020-06067-8"
- And in the interest of fairness, one that disagrees: Confronting the notion that face masks reduce COVID 'dose' https://www.cidrap.umn.edu/news-perspective/2020/11/confronting-notion-face-masks-reduce-covid-dose
Masks don’t work. At least a dozen scientific studies have shown that masks do nothing to stop the spread of respiratory viruses.
One meta-analysis published by the CDC in May 2020 found “no significant reduction in influenza transmission with the use of face masks”.
Another study with over 8000 subjects found masks “did not seem to be effective against laboratory-confirmed viral respiratory infections nor against clinical respiratory infection.”
There are literally too many to quote them all, but you can read them: [1][2][3][4][5][6][7][8][9][10] Or read a summary by SPR here.
While some studies have been done claiming to show mask do work for Covid, they are all seriously flawed. One relied on self-reported surveys as data. Another was so badly designed a panel of experts demand it be withdrawn. A third was withdrawn after its predictions proved entirely incorrect.
The WHO commissioned their own meta-analysis in the Lancet, but that study looked only at N95 masks and only in hospitals. [For full run down on the bad data in this study click here.]
Aside from scientific evidence, there’s plenty of real-world evidence that masks do nothing to halt the spread of disease.
For example, North Dakota and South Dakota had near-identical case figures, despite one having a mask-mandate and the other not:
In Kansas, counties without mask mandates actually had fewer Covid “cases” than counties with mask mandates. And despite masks being very common in Japan, they had their worst flu outbreak in decades in 2019.