Health anxiety

I have a terrible phobia of getting the flu and being sick.

I had the flu 3 times last year and missed so much work. It gave me severe panic attacks and anxiety worrying that I would get sick again.

I take 1,000mg of Vitamin C everyday, 2 Cold FX everyday, use hand sanitizer, and got my flu shot yesterday.

Is there anything else I can do to boost my immune system or keep myself from getting sick?