My extended family has all been on 125mcg(5000IU) D3 daily for 12-16 years. Most of us got CCP Flu early on in 2020. All of us immediately upon experiencing symptoms took the prescribed megadose of D3 and all but one was done with it in 8-10 hours. My son required more like 24 hours. During the time we have been taking the D3 we have experienced no other instances of flu or colds.
I’ve been taking between 5000 and 10,000 units daily since Jan 2020. Still getting at least one bad cold annually.