If I had the objective to boost my immune system, aside from a good probiotic and one medico’s recommendations of a regime of:
25,000 IU Vitamin A
10,000 mg Vitamin C
1,000 IU Vitamin D3
800 IU Vitamin E
20 mcg Selenium
300 mg Magnesium
30 mg Zinc
I would add a multi B or at least some B3 – Niacin (not the no-flush nicotinic acid)
Per this https://www.tomgrimshaw.com/tomsblog/?p=5097
If you want to go next level, go to this page and click the Ingredients tab and get more of these into your diet: https://www.healthelicious.com.au/Nutri-Blast-Immune-Blend.html