The flu shot is a guess at which viruses will be most prevalent this year. A recent study I saw (sorry, I don't have a link) suggested that a single flu shot has little impact on your likelihood of getting the flu this year. If you regularly get flu shots, however, after 4 years, your immunity is significantly increased (I presume because you have be immunised against enough different viruses).

No comment on your situation, exactly; I just thought it was an interesting and relevant factoid.