Flu Vaccine Facts
There is no single virus that causes the flu; there is no one flu vaccine that protects against all of them. A flu vaccine is designed to confer immunity against the strains of flu that are expected to be most common and most serious. The vaccine is a sort of one-size-fits-all solution, even though there are more types of flu than covered by the vaccine and the flu types vary according to region. It takes time to produce vaccines, so a new vaccine can't be instantly produced when a new type of flu starts to cause problems.
The Vaccine and Immunity
The flu vaccine gives your body parts of inactivated flu viruses. These virus parts correspond to parts of proteins floating around in your body. When the virus part contacts a chemical 'match', it stimulates the body to produce the cells and antibodies that can remove this particular intruder. Antibodies are proteins that float in body fluids and can bind to specific chemical markers. When an antibody binds to a substance, it essentially marks it for destruction by other cells. However, an antibody for one type of flu won't necessarily bind to a virus part from another type of flu. You don't get protection against other viruses. A flu vaccine can only stimulate your immune system to protect you against the viruses in the vaccine, with some lesser protection against very similar ones.
Incomplete Protection Against Intended Targets
You may not even get protection against the intended virus. Why? First, because viruses change over time. The piece that was in the vaccine may not 'look' the same (chemically) as the real thing (months later, after all!). Second, the vaccine may not have given you enough stimulation to fight off the disease.
Let's review what's happened so far: the inactivated virus piece has found a chemical match in your body. This causes an immune response, so your body has started to gear up its production of antibodies and similar markers on cells that can mark the virus for destruction or kill it outright. It's like calling up an army for a battle. Will your body win the fight when the real virus comes to call? Yes, if you have enough defenses built up. However, you will still get the flu if:
- your body isn't fast enough producing a response
- get the vaccine and get exposed to the flu too soon (less than 2 weeks)
- too much time between vaccination and exposure (loses its effectiveness over time)
- you don't produce enough of a response
- overwhelmed by exposure to a high level of the virus
- your body couldn't recognize the initial virus piece (determined by genetics)
- your body didn't make enough antibodies/cells (common in older people or people with suppressed immune systems)
- the virus as changed beyond your body's ability to recognize it
- the part of the virus that was in the vaccine can't be detected by the body in the intact virus
Waste of Time?
Yes and no... the flu vaccine will be more effective some years than others. The CDC predicted that the vaccine developed for the winter of 2003/2004 wasn't going to be effective against most cases of the flu because the strains covered by the vaccine weren't the same as the strains that were common. Highly targeted vaccines work, but only against their targets! There's no point in accepting the risks of a vaccine for a disease you can't get. When the flu vaccine is on-target, it's more effective. Even then, the vaccine isn't perfect because it uses inactivated virus. Is that bad? No. A live vaccine is more effective, but much more risky.
Bottom line: The flu vaccine varies in effectiveness from year-to-year. Even in a best-case scenario, it won't always protect against the flu. The CDC study didn't say that the vaccine didn't work; it says the vaccine didn't protect people from getting sick. Even with imperfect effectiveness, the vaccine is indicated for certain people. In my opinion, however, the vaccine isn't for everyone and certainly shouldn't be required for otherwise healthy people.