I wouldn't say it wouldn't do anything at all. It might need months to reach peak levels but any amount is helpful.

Look at the study they did in Spain recently. Patients were already hospitalized with coronavirus. They began giving one group Vitamin D and another control group nothing. The Vitamin D group had fantastic results.

Ideally, you want to be taking it before acquiring a virus or illness. But to say it's useless or insignificant if you begin taking it after acquiring the illness is simply untrue.