COVID AND THE VACCINE - TRUTH, LIES, AND MISCONCEPTIONS REVEALED, page-96973

Vit D is not enough. You also need a good vitamin C and Zinc. If you can find a place offering it you can give yourself a boost by looking into a Vit c/zinc infusion treatment. Re the D, a high quality spray is far better than a tablet, taken under the tongue before bed.

Work on your fitness and diet also and find a good doctor and get blood test (for everything) and detect any problems early. That's not just for Covid issues. Blood tests can give you feed back on you immune systems strength.