I feel that if you get enough vitamin D3 plus vitamin k2 in your system, you will most likely not get the flu if exposed, or get very mildly ill. You also need a good immune system (plenty of sleep, exercise, and pro- and pre-biotics, not much sugar in the diet). If you can manage that, you probably won’t get the flu and you won’t die from it.
If your blood vitamin D levels are below 50 and you won’t get them above thst with supplementation, you’d better get that shot, or you could get really sick. Though getting the shot is a risk each year - they don’t always nail it.
The lower your D, the more chance you will get a bad case. I learned that with double pneumonia in 3 days with the H1N1 flu before I learned about the magic of enough vitamin D. The D takes a few weeks to build up so start now. Average sized adult, 5000 IU a day - until late spring (unless you live in the tropics and get a ton of sun exposure). You might need more if you are very large or have some chronic conditions. Get tested and adjust your supplementation until it’s over 60.
I often get exposed to the flu but I haven’t gotten it again since thst H1N1 and since I started supplementing. Still soemtimes get a bad virus though. Mostly from not getting enough sleep.
Don’t take vitamin F. That will give you the flu. Actually it is the flu.