Vitamin D and immunity

Most people when I tell them about Vitamin D3 shrug it off with a grain of salt then I'll see them later sick as a dog I have been taking Vit D3 I started taking 4000iu daily in winter every second or third day in summer around 1987 right after I had just suffered one of the worst cases of the Flu that turned into Asthmatic Bronchitis that just totally laid me out right After that a friend told me of D3 So I started taking it not religiously on and off then I started getting the feeling I was getting a Cold or Flu and Started taking large doses 10,000ui right aways. It stopped it dead in its tracks Shortly after that my kids were born and I have not had a cold or flu since then I take it religiously everyday 4000iu... I heal from cuts very quickly and never get infections. For this Covid-19 Pandemic Im taking 1)Colloidal Silver Few drops under tongue daily 2)Vitamin D3 4000iu + K2 120mcg daily 3)Vitamin C 1000mg daily I also supplement with  Folic Acid, Selenium, Magnesium,