May provide some risk reduction but it will not make you bulletproof or prevent the flu. A lot of things reduce risk. Vitamin D can also be toxic in high doses. Wash your hand rest we’ll eat well take reasonable doses of vitamins if you want and you will probably get the flu anyway this year....
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You can’t make anyone “bulletproof” for a threat that they have voluntarily received year by year in a vaccine.
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WebMD says 5-20% in the U.S. on average get the flu each year, so I guess the odds are still in a person’s favor.