There's a lot of quackery surrounding this epidemic, so I thought long and hard before writing this. I have been following/researching global studies into vitamin D for nigh on a decade now.... originally it was with a view to making a television programme about it.
Vitamin D ... not a vitamin really ... it's a hormone. We produce it when certain frequencies of UV light hit our skin. If we are light skinned, we produce it more quickly than if we are dark skinned.
The headline news is that it may well have significant protective properties where covid 19 is concerned: it is crucial to the regulation of our immune systems, we have seasonal patterns of deficiency which correlate with corona virus vulnerability, it compromises this particular coronavirus' spike proteins that allow it to bind onto our cells and it helps to regulate our response to the virus. Evidence is growing that groups deficient in vitamin D (the old, diabetics, ethnic groups with dark skin) correlate with the groups most at risk from becoming seriously ill (from a virus that most people will shrug off).
I can link to a basket full of writing in the BMJ and other such reputable sources but, to be honest, it would be a waste of time. You'd be better off spending that time grabbing some high strength codliver oil capsules, vitamin D3 supplements or just exposing some skin to sunshine. It won't harm you and it night just save you from getting very sick.
If I get sick and die, you can disregard this, as I've been dosing on vit D for years.