Thread by @ReformedTrader

1/ Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers: A Randomized Controlled Trial

"95% confidence intervals are compatible w/ 46% reduction to 23% increase in infection."
acpjournals.org/doi/10.7326/m2…

2/ "During the study period (3 April to 2 June 2020), Danish authorities did not recommend masking. Use was uncommon (<5%) outside hospitals.

"Participants were randomly assigned to mask/control groups.

"Those in the mask group received 50 3-layer, disposable surgical masks."

3/ "Participants received follow-up surveys to collect information on antibody test results, adherence to recommendations on time spent outside the home, development of symptoms, COVID-19 diagnosis based on PCR testing done in public hospitals, and known COVID-19 exposures."

4/ "A recommendation to wear a surgical mask when outside the home among others did not reduce, at conventional levels of stat. significance, incident SARS-CoV-2 infection vs. no mask recommendation. We designed the study to detect a reduction in infection rate from 2% to 1%."

5/ "The findings, however, should not be used to conclude that a recommendation for everyone to wear masks in the community would not be effective in reducing SARS-CoV-2 infections, as the trial did not test the role of masks in source control of SARS-CoV-2 infection."

6/ "The face masks were high-quality surgical masks with a filtration rate of 98%.

"Face shields covering the eyes has been advocated to halt the conjunctival route of transmission, but we observed no stat. significant interaction between wearers & nonwearers of eyeglasses."

7/ "Practical challenges to implementation include potentially incorrect wearing, reduced adherence, reduced durability depending on type of mask & occupation, weather, physical & psychological discomfort, and changing to less cautious behavior due to a false sense of security."

8/ More:

Assessing mandatory stay‐at‐home and business closure effects on the spread of COVID‐19

https://twitter.com/ReformedTrader/status/1380319184110854146

Global Assessment of the Impact of Masking on COVID-19: A Country Level Comparative & Retrospective Analyses Using the Richards Model

https://twitter.com/ReformedTrader/status/1462485676293689349