Sep 29, 2021

Try https://med.stanford.edu/news/all-news/2021/09/surgical-mask... then

Abstract: https://www.poverty-action.org/study/impact-mask-distributio...

Actual paper: https://www.poverty-action.org/sites/default/files/publicati...

Sep 14, 2021

The study says:

> The intervention increased proper mask-wearing from 13.3% in control villages (N=806,547 observations) to 42.3% in treatment villages (N=797,715 observations)

https://www.poverty-action.org/sites/default/files/publicati...

Sep 08, 2021

The actual paper: https://www.poverty-action.org/sites/default/files/publicati...

The study found an effect size of zero in the cloth mask cohort, and an 11% difference in the surgical mask cohort. Effect sizes that managed significance were just barely significant, at a p-value of 0.043. Also, the researchers didn't do any baseline serology, so it's quite difficult to know if there was a starting bias influencing the final results. It's also difficult to know the degree to which the non-blinded nature of the study and voluntary seroprevalence testing biased the outcome. At such small effect sizes, questions like these matter a great deal.

Nevertheless, it is encouraging that someone actually bothered to do a proper RCT of masking as "protection for others", and this study has several points that should be widely communicated (e.g. the ineffectiveness of cloth masks). However, I would not say that "masks passed their test" is really one of them...these results are pretty mediocre.

Vinay Prasad of UCSF has made an excellent summary of the results of the Bangladesh RCT, and I recommend it strongly:

https://twitter.com/VPrasadMDMPH/status/1435679462142607361

Sep 03, 2021

It did: "Blood samples were collected from N=10,952 consenting, symptomatic individuals."

From https://www.poverty-action.org/sites/default/files/publicati... , pg 2, Abstract section, para 2

Sep 03, 2021

"This report" does gloss over much of the results from the actual study. Here's the link to the paper:

https://www.poverty-action.org/sites/default/files/publicati...

Sep 03, 2021

Here is the paper (or one of them, it is not clear after so many links):

https://www.poverty-action.org/sites/default/files/publicati...

Bottom line: "The proportion of individuals with COVID-like symptoms was 7.62% (N=13,273) in the intervention arm and 8.62% (N=13,893) in the control arm. Blood samples were collected from N=10,952 consenting, symptomatic individuals. Adjusting for baseline covariates, the 2 intervention reduced symptomatic seroprevalence by 9.3% (adjusted prevalence ratio (aPR) = 0.91 [0.82, 1.00]; control prevalence 0.76%; treatment prevalence 0.68%). In villages randomized to surgical masks (n = 200), the relative reduction was 11.2% overall (aPR = 0.89 [0.78, 1.00]) and 34.7% among individuals 60+ (aPR = 0.65 [0.46, 0.85]). No adverse events were reported."