If you're taking skin color into account (european descent in other words) then you should also take geography into account. A lighter skin in southern latitude vs. darker skin in northern latitudes. It's not a simple thing but I do believe vitamin D had a big role to play to boost immune systems. We've been using it for years here in Sweden, every winter. I even found a video online from a local TV channel that was recorded in 2019, reviewing different brands of Vitamin D and suggesting how many IUs you need every day.