I think you will find some of the information in this article on Mercola.com very helpful. The info on Vitamin D deficiency is particularly enlightening, so scroll down to it if you don't want to read the whole article, although I'm sure you will be encouraged by the info on Vitamin C, also.
The premise is that many people are deficient in Vitamin D, especially in the winter months when we are not in sunshine so our bodies are not able to synthesize Vitamin D. This time frame coincides with when the flu is most prevalent. It also says that darker skinned people need more sun exposure to synthesize enough vitamin D to bring them up to safe levels so they are even more prone to Vitamin D deficiency than the general population. Could this be why Covid-19 has affected more blacks?
I believe, the whole idea of vitamin deficiency is an interesting concept to consider when looking for causes of illness. Country Guy and I take several supplements which include Vitamin C, D, zinc, lysine, and astazanthin among other things.
Another good site for more information on the importance of Vitamin C, lysine and other micronutrients in the treatment of cancer, multiple sclerosis, heart disease, etc, is Dr. Rath's website: https://www.dr-rath-foundation.org/category/cellular-medicine/