Trish Greenhalgh
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1. Thread on masks (also posted on Twitter). Addresses:
- Why so much controversy?
- Airborne transmission
- RCTs of masks – strengths/limitations, community, healthcare settings
- Meta-analyses – gold standard or lazy lumping?
- Non-RCT evidence – why is it needed, what does it show?
- AOB
09:16 AM - Feb 26, 2023
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Trish Greenhalgh
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In response to Trish Greenhalgh.
2. Before I start, here’s my OLD mask thread from Twitter July 21, which ran to >100 tweets. Some of that is now rather dated but a lot still holds. I’ll paste the best from that into this new thread. Will take a while (~100 total)
https://twitter.com/trishg...
09:17 AM - Feb 26, 2023
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Trish Greenhalgh
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In response to Trish Greenhalgh.
3. WHY IS MASKING SO CONTROVERSIAL?
First, ‘masks’ and ‘masking’ are very broad terms. They cover different technologies (cloth, medical, respirator), wearers (public, patient, healthcare worker), settings (low v high risk) and requirements (mandated v free choice).
09:18 AM - Feb 26, 2023
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Trish Greenhalgh
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In response to Trish Greenhalgh.
4. WHY CONTROVERSIAL?
Because of this multiplicity, statements like “masks [don’t] work” may be referring to very different interventions in different populations for different activities at different times, not to mention different diseases. The literature, in short, is a mess.
09:18 AM - Feb 26, 2023
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Trish Greenhalgh
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In response to Trish Greenhalgh.
5. WHY CONTROVERSIAL?
Second, masking is a cultural practice as well as a public health intervention. It has symbolic meaning. Pirates and burglars wear masks. To some, masking means you’re a ‘pansy’, ‘sheep’ etc. Masking offends libertarians.
https://www.bmj.com/conten...
09:19 AM - Feb 26, 2023
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Trish Greenhalgh
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In response to Trish Greenhalgh.
6. WHY CONTROVERSIAL?
There’s strong social pressure to mask in some settings to contribute to the greater good (“my mask protects you”). People may feel pushed into doing something which a) feels awkward, b) symbolises an allegiance they don’t identify with and c) they feel is ineffective.
09:20 AM - Feb 26, 2023
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Trish Greenhalgh
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In response to Trish Greenhalgh.
7. WHY CONTROVERSIAL?
Third, masking (whatever its benefits) has some downsides. It’s (depending on the design) uncomfortable. It can interfere with communication (especially if hard of hearing). If you work long shifts, it gets hot/sweaty behind the mask.
https://www.bmj.com/conten...
09:20 AM - Feb 26, 2023
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Trish Greenhalgh
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8. WHY CONTROVERSIAL?
In short, masking is something many of us feel strongly about. It’s not even possible to separate “the science” of masks from “the politics”, since science does not sit in some protected bubble away from the rest of society. Read on!
In response to Trish Greenhalgh.
09:21 AM - Feb 26, 2023
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Trish Greenhalgh
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In response to Trish Greenhalgh.
9. AIRBORNE TRANSMISSION
Understanding why & to what extent masks work requires knowledge of how the SARS-CoV-2 virus is transmitted. With colleagues, I published this summary of evidence that it spreads *predominantly* via air. https://twitter.com/trishg...
09:22 AM - Feb 26, 2023
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Trish Greenhalgh
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In response to Trish Greenhalgh.
10. AIRBORNE TRANSMISSION
I responded to critics of that paper here https://twitter.com/trishg... (plus see more in thread below).
09:22 AM - Feb 26, 2023
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