For those parents who may be worried about the pain of the injection or the possibility of symptoms after the flu shot, I will leave a note about my experience.
I have a two year old daughter who recieved her flu shot about 2 weeks ago. She had very little reaction to the actual injection. She didn't even cry! She just grunted once and hopped down and was on her way. She also had no symptoms such as fever, runny nose etc. I think even if your child does get symptoms that they are probably going to be mild enough that it is still worth it to vaccinate.
I know as parents we don't want to do anything that inflicts pain on our children, but in this case it is far better to take them for a shot than to let them get sick.