A very good thread on that Danish mask paper
https://twitter.com/trishgreenhalgh/status/1329163949732933633 …
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Replying to @MackayIM
Not sure I agree with the "too short" point - they tested IgM as well as IgG and from my understanding that should be detectable much earlier than 2 weeks? Also included PCR+ in their main analysis
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Replying to @GidMK
No baseline PCR test from what I could interpret. Only a self-collected swab at the end of a month. About 7-10d for IgM to peak. IgG can sometimes precede, sometimes accompany appearance of IgM
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Replying to @MackayIM
Sure, but if you had a 30-day PCR, IgG and IgM surely you wouldn't expect to have missed many cases?
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I mean, there's some possibility that none of these tests would pick up someone who got infected right at the end of the study period, but surely you'd expect it to get most of them?
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Replying to @GidMK
You would. Just not clear what % may have been infected already, still shedding RNA but not yet having developed a detectable Ab response. But as you say, it was randomised.
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Replying to @MackayIM
Yeh, I don't think the criticism makes sense tbh. If it was powered sufficiently, and the endpoint (AB/PCR+) is reasonable, then saying it's too short is wrong
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Replying to @GidMK
I'm still not clear on what's wrong with "If you get infected in that period, the incubation period may be up to 14 days, so you may not turn positive till after the end of the study."
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It doesn't matter in terms of the results of the trial. Unless the suggestion is for an effect that differentiates between arms, they still had enough cases to detect a 50% difference even if lots of people were infected but couldn't be detected
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(Whether a 50% reduction from 2% to 1% in infection rate is likely and reasonable to power a study is another question entirely. I would say probably not, no one would suggest that's likely!)
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