Unfortunately it is the opposite for me

I can't take multi vitamins because they (or something in them) affect my liver
I can't take vitamin C tablets because anything with a citrus base (or citrus in general) cause great pain and inflammation to my joints.

Touch wood - over 4 years and not a cold or flu yet (a sore throat for a day or two only)

However the answer to your question is, yes you can have normal dose vitamin C daily.

Flu shot, in the end, is your choice......just not a live vaccine