Originally Posted by r2473
You've had the flu and not suffered at all (had no symptoms)? I'll have to take your word on that. Or do you mean that you had the flu virus, but since you had the flu shot, your body was able to rid it from your body before you got sick with symptoms?
Generally speaking, flu's are more severe than colds.
I also think you can just check for fever. You might get a very mild fever with a cold (but usually not, unless you are a kid), but will always (nearly always?) have a fever with the flu.
This CDC article basically agrees with us both. It says that it is impossible to tell the two apart, but suggests common symptoms associated with each.
I'm editing this to make clear that when I say "having the flu" I'm talking about exposure to the virus, not necessarily the nasty symptoms. I'm just suggesting that it is possible to be exposed to a virus and have an immune system response without necessarily suffering from a nasty infection. So, this would suggest exposure to the virus not getting sick.
Again, I'm not an expert on this subject, but I do believe that it is possible that exposure to a virus doesn't necessarily mean a rip-roaring infection. As I understand it, a virus is a piece of genetic code usually in a hard protein cover that hijacks cells to reproduce. As I understand it, these viruses are extremely common, though luckily not all of them cause infections.
If your immune system is healthy, it should seek out viruses that are causing trouble and destroy them so they can't keep hijacking cells and reproducing. I've done stupid things like accidentally drink out of glass someone else with an active flu symptoms was using. My assumption is that I was exposed to the virus even though I didn't develop any symptoms of an infection. Perhaps I was never infected or perhaps my immune system cleared it before it caused any noticeable trouble.