Earlier quoted context omitted.
Like a lot of things, vitamin D may have a slight effect on COVID mortality rates, but won't accomplish much by itself. Edit: The study linked below is pretty compelling. My comment appears to be incorrect.
The studies I saw, many of which were posted here, recorded dramatic impact on disease severity from Vitamin D alone. https://www.sciencedirect.com/science/article/pii/S096007602...
Vitamin D supplementation is a low-risk, low-cost, side-effect-free (hard to OD) intervention. I see no reason governments should not encourage vitamin D supplementation (or, better yet, actively enable it via distribution of supplements as in the UK...at least during hospital stays). If it turns out that subsequent RCTs disprove the effects (despite the mountain of retrospective studies that show correlations in vitamin D levels and covid case trajectories), what harm will have been done?