[rndgermandude]

What is usually measured is the calcifediol - aka 25(OH)D - in the blood. It is the liver that produces calcifediol from cholecalciferol - aka vitamin-D3. The kidneys (mostly) then turn that in calcitriol, the actual hormon.

Vitamin-D2 aka ergocalciferol works similar in that is is eventually converted by liver and kidneys into calcitriol.

Ergocalciferol, calcifediol and it's various precursors can indeed be stored in fat tissue.

It is unclear however how severe covid-19 can affect the kidney and liver functions relating to this and release of substances from fat tissue.

Right now a lot of research seems to point in the direction that vitamin-D deficiency can indeed lead to more severe covid-19. At the same time there is different research suggesting that covid-19 itself messes with vitamin-D levels as well.