Definitely. The last time I took a vitamin (more specifically, AirBorne) was a few years ago when I started getting a cold. Took the stuff religiously as per the instructions; within a few days I was bedridden with the flu. I've never felt sicker in my life. ...Haven't touched a vitamin since.
You know the saying, "if you cure it, it lasts 7 days; if you don't cure it, it lasts a week."
hmmmm... interesting. i've never tried airborne but i take 2k mg vitamin C everyday and up to 4-5k mg whenever i feel that i might get sick. when i had midterms earlier this year, everyone (roomie, lab partner, ppl who seat around me in lecture halls) got a flu. but i managed to keep the bug out until after the midterms, and it only took me 2 days to recover. also, i only had mild running noise and didn't even look sick during those two days.