I was hoping for some informed reference to medical research here, but I don't see any. Anecdotal evidence only goes so far. My experience is that flu shots help, but I don't think that means anything.
There must be hundreds of large-scale studies. You would have to look at them with a suspicious eye, because you never know who pays the research grants. But usually you can find some sort of helpful statistical information on this kind of thing.
PS, I just tried to do a Google search on flu shot statistics, and turned up nothing but garbage and vague assurances. Somebody knowledgeable needs to get into this discussion.