When I feel the coming of cold or Flu symptoms I take up to 3000 mg of either pill or powder C and the symptoms disappear. To me C is a good immune booster.
I'm glad someone else said this because it's the same way for me.
Literally last Thursday I was sitting at work, when I felt body aches and scratchy throat coming on. So when I get home (as usual) I popped 3,000mg's of VitC, sprayed some coilloidal silver on my throat, then went to bed. I would proceed to pop another 3,000-4,000mg's on Friday. Then by Saturday I woke up fine - albeit a bit of phlegm in my chest but that's normal when you break whatever it is before it gestates into something much worse.