This far into the pandemic there is no excuse for denying masks reduce the transmission of COVID-19. I’m making this thread to be a quick reference of the evidence so you can refer people here if you find yourself faced with the claim “masks don’t work.”
Article published in JAMA in 2/2021 detailing how masks work to reduce community transmission. Include a nice table summarizing 11 studies at the time. jamanetwork.com/journals/jama/… 
A study from JAMA in 7/2020 of almost 10,000 healthcare workers showing universal masking in the healthcare setting decreased cases. jamanetwork.com/journals/jama/…
Large systematic review and meta analysis from the Lancet in 6/2020 showed masking reduced transmission (as well as social distancing and eye protection). thelancet.com/journals/lance…
Another systematic review and meta analysis from the American College of Cardiology in 9/2020 showed significant reduction in transmission for both healthcare and non-healthcare workers. acc.org/latest-in-card…
A cross-sectional study in the Lancet from 1/2021 showed face masks and physical distancing reduced transmission. thelancet.com/journals/landi…
From JAMA now in 2/2022 masks cut secondary transmission in half.
jamanetwork.com/journals/jama/…
jamanetwork.com/journals/jama/…
I found this to be a nice summary at the time (8/2020) from BYU on “Making Sense of the Research on COVID-19 and Masks.” pws.byu.edu/covid-19-and-m…
This was also a nice informative article at the time (4/2020). Keep your droplets to yourself. fast.ai/posts/2020-04-…
Nice one from Science 5/2021 discussing how masks limit transmission probability especially if combined with distancing and hand hygiene. science.org/doi/full/10.11…
Nice study from 5/2022 showing direct mask wearing (as opposed to prior studies of mask mandates) reduced transmission. pnas.org/doi/10.1073/pn…
And another all the way back from 12/2020 showing masks reduce transmission. pnas.org/doi/10.1073/pn…
Large study from Standford in 9/2021 showing surgical masks can reduce transmission. med.stanford.edu/news/all-news/…
Another systematic review this one from 1/2021 frontiersin.org/articles/10.33…
Andddd another systematic review this one from 7/2021 sciencedirect.com/science/articl…
This study in preprint from 11/4/2022 showing mask policies reduced transmission rates. medrxiv.org/content/10.110…
A study showing even after high levels of transmission adoption of mask wearing reduces spread and death. medrxiv.org/content/10.110…
Wearing a mask in care homes reduced spread. academic.oup.com/ije/article/50…
Another systematic review from 7/2022, surprise surprise, masking reduced transmission. medrxiv.org/content/10.110…
Fabric masks better than nothing? 🤷♂️ tandfonline.com/doi/full/10.10…
What about schools? Well new article from 11/9/22 in the NEJM shows it can help. nejm.org/doi/full/10.10…
Study from the AAP 5/20/2022 publications.aap.org/pediatrics/art…
From the NIH nih.gov/news-events/ni…
Adding this study from 10/2022 showing masking in classrooms slowed the spread. mdpi.com/1660-4601/19/2…
Of course need to add this study from 8/2022 on school masking requirements that made the rounds all over Twitter at the time. medrxiv.org/content/10.110…
Adding this study from 10/6/22 showing masking continued to be helpful even with Omicron. ajicjournal.org/article/S0196-…
And because this keeps coming up in the comments here is a RCT study from February 2009 showing *proper* mask use was associated with a 60-80% reduction in transmission of influenza like illnesses. ncbi.nlm.nih.gov/pmc/articles/P…
And another RCT from February 2010 showing masks and hand hygiene reduced influenza like illnesses. pubmed.ncbi.nlm.nih.gov/20088690/
A nice companion article to the above study: academic.oup.com/jid/article/20…
This is such a great article that covers a little bit of everything. The section on masking is definitely worth reading. sciencedirect.com/science/articl…
Paper also has a nice section on Misinformation. sciencedirect.com/science/articl…
Adding this paper from Nature 12/2/22 because masking reduces exposure to and spreading of higher viral loads. Lower viral loads = less transmission. Mask up. Bonus points because vaccination also reduces peak time of viral loads. nature.com/articles/s4157…
Adding this study from April 2020 showing surgical face mask use can lower both influenza and coronavirus in aerosols. Mask up this season people.
nature.com/articles/s4159…
nature.com/articles/s4159…
Clinical review from the BMJ in 2015 looked at 9 studies with all but one showing masks or masks plus hand hygiene can lower transmission of respiratory viruses. bmj.com/content/350/bm…
Study from 2009 showing both N95 and surgical masks reduced spread of influenza. academic.oup.com/cid/article/49…
Study from 2013: Surgical masks worn by patients reduce aerosols shedding of influenza virus. journals.plos.org/plospathogens/…
Study from 5/2011 showing N95s gave superior protection against respiratory viruses. pubmed.ncbi.nlm.nih.gov/21477136/
Study from 1/11/23 out of BC found face mask impacts were greatest in restaurants, bars, cafés, and retail locations. publichealth.jmir.org/2023/1/e42616
Nice update from this past fall reviewing the evidence for mask wearing to prevent COVID. After review call on the ice stands, masks work. ncbi.nlm.nih.gov/pmc/articles/P…
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