From a commenter:
Also, worth noting that this is not a “pre-publication” version of a manuscript in the usual sense of the term. “Pre-publication” usually refers to an online publication of a reviewed manuscript that precedes formal publication and are usually pdf’s of a word document. This is a paper uploaded to the medRxiv preprint server. These “preprints” are not reviewed except only for some basic formatting and editorial issues regarding reporting and ethical standards.
This is the statement on the home page of the MedRxiv website:
Caution: Preprints are preliminary reports of work that have not been certified by peer review. They should not be relied on to guide clinical practice or health-related behavior and should not be reported in news media as established information.
I hope all of us here who are eager to convey information about Covid-19 take this caution into account before posting or, at the least, include such a disclaimer in their diaries. There is too much premature and false information going around as it is.