Vitamin D may have modulatory effects on the biochemical pathways linked in the original article. Most pharmaceutical products we study aren't going to directly kill bacteria or viruses, usually they have a particular physical effect on a specific molecule that then leads, through various cellular pathways, to the death or suppression of the pathogen. I highly doubt Vitamin D directly kills anything, it could modulate symptoms or the pathophysiology of COVID-19 the disease, vs. SARS-COV-2 the virus itself.
If "it" means UV light, yes there are UV sterilizers aplenty today. If "it" means outdoors/fresh air, there are a lot of components to that and it's not like "fresh air" enters "in vivo" per se.
Yes, I'm aware of UV sterilizer, but does it work when the microorganisms are inside you? You don't want to get an "internal tan"
