The studies with positive results are suggesting somewhere around a one binary order of magnitude reduction in risk of infection with possibly some reduction in severity of cases. I'd suspect that the health authorities would not be reluctant to promote a vaccine that had similar results if none better becomes available. Some hospitals are supplementing vitamin D for Covid-19 patients. Trump got it.
It is interesting that with this much evidence, public officials are not telling us to take VitD.
The masses are crazy though - VitD can be a little dangerous and I can see quite a lot of people taking '10x doses' to get '10x protection' and ending up in the hospital anyhow.
I saw an article posted someplace a couple of weeks ago telling the story of one person who suffered from too much VitD -- but that person wound up in the hospital only after taking 78000 units/day for about 8 months. That article would have been misleading then if one inferred from it that you really have to seriously knock yourself out to do any damage?
