Long thread coming: mute if not interested.

The DANMASK19 RCT of masking in Covid-19 prevention has been published. I have serious concerns. I’m deliberately not linking to the paper.

DANMASK19 was an unblinded RCT of surgical mask wearing to test if they protect the *wearer* [did not look at source control], led from a Copenhagen hospital and recruiting ~6000 people via media ads.

As far as I can see, there was
-no involvement of a clinical trials unit
-no data monitoring group
-no reference to CONSORT criteria
-no formal ethics approval

Authors state that a regional ethics committee “did not require” ethics approval for a study involving *swabs and blood tests on 6000 people*. This seems very odd. Suspect REC may have said a community study was outwith their remit.

Intervention group were sent a kit and asked to wear a mask when went out; controls asked to not use masks. Self-administered Ab test the day intervention began and the day it ended, plus self-administer swab at end of the study and if became symptomatic during it.

Intervention period was *30 days*. This is VERY SHORT. 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. Prevalence of Covid-19 at time of study was low.