From Dr. Gerberding's own mouth according to a CDC news conference transcript which can be found at http://www.cdc.gov/media/transcripts/t031209.htm:
"How we know what's in flu vaccine is to look at the flu strains that appear toward the end of the last flu season. And it's a race. We've got to find the strains, we've got to characterize those strains, they have to be grown in tissue culture and grown in eggs because the manufactured virus comes from egg cultures. And all of this has to happen very, very quickly because it takes awhile for the vaccine production to occur and for the many steps that have to deal with the purity, the concentration, and the overall product security of the vaccine that emerges. And that all has to happen in time for the product to be distributed and available for people before the beginning or at the beginning of flu season.
"But we really need to know what's going to be in the next year's
flu vaccine by somewhere around February if we're going to go through
those steps in time to make the vaccine available and distribute it.
And that's really tough to do as the situation evolves. We can have a
more lead time in some years, but you've got to have a pretty good
guess and get the ball rolling."
Dr. Gerberding goes on to say:
"First of all, in terms of vaccine failures, every year there are vaccine failures, even if there's a perfect match between the vaccine and the strains of virus that are circulating in the community because the vaccine is not 100-percent efficacious. So we have situations this year where we are evaluating the possibility of vaccine failure, but that's not at all unusual. We won't be able to say anything concrete about the efficacy of this year's vaccine until we are much further into the flu season, and we have much more data than we have right now, but obviously it's an important question that we're working hard to evaluate."
And here's some info from the package insert about possible "adverse reactions":
The following additional adverse reactions have been reported during post-approval use of FLUVIRIN®. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to vaccine exposure. Adverse events described here are included because: a) they represent reactions which are known to occur following immunizations generally or influenza immunizations specifically; b) they are potentially serious; or c) the frequency of reporting.
Body as a whole: Local injection site reactions (including pain, pain limiting limb movement, redness, swelling, warmth, ecchymosis, induration), hot flashes/flushes; chills; fever; malaise; shivering; fatigue; asthenia; facial edema.
Immune system disorders: Hypersensitivity reactions (including throat and/or mouth edema). In rare cases, hypersensitivity reactions have lead to anaphylactic shock and death.
Cardiovascular disorders: Vasculitis (in rare cases with transient renal involvement), syncope shortly after vaccination.
Digestive disorders: Diarrhea; nausea; vomiting; abdominal pain.
Blood and lymphatic disorders: Local lymphadenopathy; transient thrombocytopenia.
Metabolic and nutritional disorders: Loss of appetite.
Musculoskeletal: Arthralgia; myalgia; myasthenia.
Nervous system disorders: Headache; dizziness; neuralgia; paraesthesia; confusion; febrile convulsions; Guillain-Barré Syndrome; myelitis (including encephalomyelitis and transverse myelitis); neuropathy (including neuritis); paralysis (including Bell’s Palsy).
Respiratory disorders: Dyspnea; chest pain; cough; pharyngitis; rhinitis.
Skin and appendages: Stevens-Johnson syndrome; sweating; pruritus; urticaria; rash (including non-specific, maculopapular, and vesiculobulbous).
And since it's nearly impossible to find a listing of ingredients for the flu shot unless your last name is Holmes, I've done the research for you (with comments, of course) in an older post which you can read here: http://triumphtraining.com/blogs/blog/6364442-365-ways-300-flu-shot-ingredients