nickname - Member
I'll give them a whirl, can't do any harm I guess
Have a look on the internet, and read many publications (a good place to start being sciencedaily.com) and the "can't do any harm" thing is effectively rubbished. Short term, unlikely, long-term most probably.
If you're going to take anything to boost your immune system, take a probiotic such as acidophilos lactobilis (or something with the lacto in it anyway), as that promotes the healthy bacteria in your gut which is a key source of immune protection. I wouldn't bother with all those actimel / activia things - you can equal them with a good diet.
Above all, a good diet is what's needed and should negate the need for any supplementation except at times of significant stress on either mind or body, which has been proven to weaken the immune system.
If you do want to take a vitamin, the one I would recommend is the "reflex nexgen", as this contains the vitamins and probiotics. Equally, I would quarter their recommended dose - i.e. one a day instead of 4.
That's my take on it, and I've been well all winter.