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THREAD: How do we know that masks are effective? Want proof, to show mask-skeptic friends? Here's a thread full of evidence.
It's medically unethical to do clinical testing in which we directly expose people to COVID-19 with & without masks. So scientists test other ways.
It's medically unethical to do clinical testing in which we directly expose people to COVID-19 with & without masks. So scientists test other ways.
2. One of the ways scientists assess mask effectiveness is by looking at community spread in areas of the US before and after mask mandates are issued, such as in this study:
https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818
https://www.healthaffairs.org/doi/10.1377/hlthaff.2020.00818
3. Another way is by examining COVID-19 death rates (taking into account other relevant factors) in countries where the population wears masks, such as in this study: https://www.researchgate.net/publication/342198360_Association_of_country-wide_coronavirus_mortality_with_demographics_testing_lockdowns_and_public_wearing_of_masks_Update_June_15_2020
4. Another way is by conducting a meta-analysis of COVID-19 containment measures (including masks) in various countries, to check their effectiveness, such as in this broad study: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)31142-9/fulltext#%20
5. Another way is by measuring the effectiveness of surgical masks in capturing various respiratory viruses (including coronaviruses) exhaled while breathing: https://www.nature.com/articles/s41591-020-0843-2
6. Another way is by testing how well different fabrics (used in cloth masks) can block viral particles, such as in these 2 studies:
https://pubs.acs.org/doi/10.1021/acs.nanolett.0c02211?ref=pdf
https://www.medrxiv.org/content/10.1101/2020.04.17.20069567v2.full.pdf
https://pubs.acs.org/doi/10.1021/acs.nanolett.0c02211?ref=pdf
https://www.medrxiv.org/content/10.1101/2020.04.17.20069567v2.full.pdf
7. Another way is by studying the trajectory of droplets (which can contain COVID-19 particles) released into the air when humans speak, and how they are blocked by a fabric covering: https://www.nejm.org/doi/full/10.1056/NEJMc2007800
8. Another way is by tracing COVID-19 spread from a single infected mask-wearing individual in a closed setting with others - here are 2 such cases:
https://www.cmaj.ca/content/192/15/E410
https://www.washingtonpost.com/business/2020/06/17/masks-salons-missouri/
https://www.cmaj.ca/content/192/15/E410
https://www.washingtonpost.com/business/2020/06/17/masks-salons-missouri/
9. Another way is by running simulations (a.k.a. using scientific models) to predict the effect of maskwearing on COVID-19 spread:
https://arxiv.org/pdf/2004.13553.pdf
https://royalsocietypublishing.org/doi/10.1098/rspa.2020.0376
https://arxiv.org/pdf/2004.13553.pdf
https://royalsocietypublishing.org/doi/10.1098/rspa.2020.0376
10. This isn't everything, but it gives you a sampling of the ways scientists have determined that masks are protective. Cloth masks offer some level of protection - some more than others. None are useless.
Here is a helpful review of evidence:
http://files.fast.ai/papers/masks_lit_review.pdf
Here is a helpful review of evidence:
http://files.fast.ai/papers/masks_lit_review.pdf
@GilbertSundevil, you wanted to see the studies about mask effectiveness. I promised I'd show you the studies today. Here's a sampling of them.
