I think you have to be loaded up on D3 BEFORE you contract the virus. And you need to be taking it with K2.
Since my son in Special Forces told me he had been advised to take 5000 IU of D, I have added from 2000 to 4000 IU daily. I had been taking K2 but ran out, so better get some more. For over 45 years I have been taking 3 to 6 grams Vitamin C spread thruout the day for my allergies. Dose varied depending on symptoms of clogged nasal passages and sneezing. If I start housecleaning (house dust is one allergy) and my symptoms start, I immediately take 1 or 2 grams and they go away soon. At 81 I am in good health and hope to remain that way.