Zinc is probably essential in this, but Vit D acts as a hormone to modulate the immune system so it doesn't overreact as well. It can prevent the cytokine storm reaction that supposedly occurs in the lungs by this infection. Most of us are Vit D deficient anyway. The USDA is laughable.(400iu daily?) I take at least 10,000 IU of good quality ( non-soy sourced) Vit D a day with K2. I can't recall where I read it ,but not one patient with a Vit D level above 30 mg/dl was hospitalized in those tested. The sweet spot is about 60-80 mg /dl.
If you are out in the sun with significant skin exposure at prime time ( 12pm-2pm) for 15 minutes, Your body will make 25,000 IU of Vit D itself. (You shouldn't burn at 15 minutes)