It's more than likely simply an irritation from getting the shot, not an actual allergic reaction. Anaphylactic reactions are generally very quick in their onset and very serious things.
That all being said, flu shots work for plenty of people... especially those at high risk to get the flu. My dad gets one every year, since he's a physician and is obviously around sick patients on a regular basis... he's never gotten the flu. My ex-wife got flu shots when we both worked at a medical clinic... ironically enough though, she got the flu the first year and I didn't (I never get the flu shot). I could go on, but there's no real point in doing so. People make decisions on what they feel is best in their given situation Dana, and they are effective for the majority of the population. I choose not to get a flu shot simply because I'm deathly afraid of needles, otherwise I'd probably have it done if just to help mitigate the risk of getting the flu somewhat.
But in typical Dana fashion, you have to act like a complete fucktard about it.