Glad this study was published (go science!!) but there are SO MANY CAVEATS that it literally changes NOTHING about our knowledge about recs to #MaskUp .

You'll be hearing a lot about this, so let me break it down. https://twitter.com/CaulfieldTim/status/1329100810081374209

1) Most impt: Very wide confidence intervals (-43% to +23%) suggest that they were underpowered, likely due to low community prevalence (not enough people exposed to possible infection).

This makes it impossible to draw conclusions.

2) The intervention was sub-par.

They didn't follow best practice. It was SINGLE masking. Despite extensive evidence that BOTH PEOPLE wearing masks = much better:

as they say "the trial did not test the role of masks in source control of SARS-CoV-2 infection"

3) Additionally, there were a lot of confounders:

* only 46% of ppl wore the masks as intended!!

* the trial started DURING LOCKDOWN when everyone was distanced

* face mask group took fewer social precautions

Hmm.

4) I do like that follow-up included both PCR + antibody tests. A nice touch that increases confidence in results.

5) But weirdly, the % with household contacts who were +, who got infected, was ridiculously low c/w other studies?

Their conclusion: "these findings do not provide data on the effectiveness of widespread mask wearing in the community."

I AGREE.

Takeaways:

This study does NOT contradict existing studies on the efficacy of universal masking.

No healthcare worker will stop wearing a mask bc of this study. Neither should you.

cc @TheSGEM @CaulfieldTim for calling it to my attention and @AnnalsofIM who printed it!