A study of vitamin D blood test level and severity of COVID-19 is breathtaking!
96% of people with a mild case of the virus did not have low or low-normal vitamin D. (>29 ng/mL)
Roughly half of the people with severe and critical cases of the virus had low vitamin D. Fewer than 5% of those people did not have low or low-normal vitamin D
Even in people who had an "ordinary" case of the virus, only 7% of them did not have low or low-normal vitamin D.
I think that makes low or low-normal vitamin D the biggest risk factor for the virus.