I decided it might be easier to comment further on my status(es) yesterday about flu shots and flu antibodies in a blog than to add my own replies or bounce around to several pages.
First, the source for the answer that I found was on the same site as COXBETH provided on my second status, but a different page:
This page has a lot of good information, in question and answer form, on things like how the decide which viruses to protect against and why some people will still get sick with one of those even after. It definitely has the agenda of convincing the reader that they should get the flu shot (influenza vaccination) every year, early rather than late, but looking past that at the studies and factual answers, it is possible to draw one's own conclusions.
My core question had to do with whether or not immunity to the flu viruses built up year to year for someone consistently getting the flu shot. I knew they only had selected viruses protected against each year, but would last year's shot still protect against those same viruses this year?
There's two parts to the answer. One is that the amount of antibodies in our blood goes down over time, so we gradually become more likely to get sick. The other is that viruses tend to change over time, so the "same" virus isn't really the same any more - even if it has the same basic attributes.
The point that was interesting to me is that it doesn't matter whether we get those antibodies from actually catching and fighting off the flu virus or from getting a flu shot - the protection wears off the same. Of course, most people don't want to suffer through a serious bout of the flu just to get the antibodies to avoid getting sick with it again for a while. Hence the flu shots.
(I also learned that H1N1 was in both last year's and this year's shot, which made me wonder if that was more for those who may not have gone in for the shot last year -- or because the antibodies can decline that quickly. I'm guessing the former or a mix of both.)
It is definitely possible to still get sick after being vaccinated - and they list three reasons:
1) Exposure just before or within a short time after getting the shot. (Shots aren't instant immunity - they simply trigger your body to begin producing antibodies to fight. That takes up to 2 weeks.)
2) A different virus. The shot protects against three strains. The antibodies may help protect somewhat against others, but that protection may not be complete. (Sometimes it means being less sick than one would be otherwise.)
3) Health and age factor into how well our body produces antibodies in response to the vaccination. Some people can even get sick from one of the strains that the flu shot was meant to protect against (not from the shot, but from later exposure).
(In addition to those reasons, not everyone who gets sick and calls it the flu has the influenza virus, whether one of those they should have been protected against or a different one. Anecdotal evidence lacks confirmation from a lab that an influenza virus is involved. In addition, we won't often hear the opposing anecdotes. A doctor is only going to see the people who did get sick ... and have no frame of reference in numbers for those who didn't get sick because they didn't need to come see him.)
Now, all that said, that doesn't mean we should avoid the flu shot because "it doesn't work".
ALERT: These next numbers are made up just to provide a reference. The actual numbers are probably in studies out there.
For example, if 100 people got flu shots and 10 of them got sick with an actual influenza virus within the next 8 months, that's 90 people who did not. How many of those 190 would have gotten sick without the shot? That can be a difficult question to answer. We aren't testing the healthy people constantly to see if they've been exposed and avoided getting sick; we're tracking records on those who get sick and go to the doctor.
To try to answer that question, historical data is used. If we have data that in past years with no flu shot option at least 25 people out of 100 came down sick with the flu, then we compare the 10 to the 25 and say it was definitely effective - 15 people were protected.
Back to real numbers. From a report giving early estimates of the effectiveness: "Results for the 2012–13 season indicate that vaccination has reduced the risk for influenza-associated medical visits by approximately 60%". That is similar to what HOPEFULHIPPO mentioned of the news saying it was "less than 60% effective".
It also shows very well how wording can make the same data sound like it means very different things. Approximately 60% and less than 60% could both mean 58% or 59%, but by saying "less than" the news source makes the implication that it is less than effective. Another point in the article actually gives 62% and a range from 51% to 71%. Turn it around and say "more than 50% effective" and it sounds a lot better. Facts CAN be twisted in either direction.
I'll end with the comment that, no, I don't get the flu shot and don't plan to. My reasons actually have little to do with effectiveness or lack of it.
1) I rarely ever get sick. Once a year at worst I get sniffles, touch of a sore throat, a cough if the sniffles go down my throat at night. A few times a year I might go through a day of being oddly exhausted and having chills then a quick fever. I consider those a sign that I was exposed to something and my body did its job and successfully fought off the infection. Getting sick with symptoms is when it doesn't fight it off as quickly and efficiently. My immune system is in good order tackles any virus I don't manage to avoid through simple precautions of washing hands, etc.
2) I'm not around very young children, the elderly, or anyone considered at a higher risk. Being a carrier could be a concern if I was, but I'm also vigilant about the times I feel off to avoid exposing others unnecessarily.
3) My own personal belief system is that one develops and maintains a strong immune system by BEING exposed and fighting things. I have kind of a twisted take on evolution which says I want to survive current things because I'm fit to do so. When studies say we evolved to be certain ways, my thought is that our changing and adapting doesn't end at some past point in time. I'm not living in the world of my evolutionary ancestors, so I don't need to alter my world to mimic theirs -- I need to be fit to survive in mine.
And just maybe a small part of it is reminiscent of my vaccination history as a child. My parents abstained for religious reasons in the early years. I had the mumps, I had the measles, I had chicken pox. The religious reason had to do with the way the shots were made at the time, in that they included some blood components - and Jehovah's Witnesses very firmly hold to a "no blood" rule - not eaten, not transfused, and not entered into the body in any way, including shots. I was around 10 when they believed the shots to be "safe" in those religious terms. I got the MMR (Measles, Mumps, Rubella) shot and wondered why on earth I needed it when I'd already had two out of three ... and neither of those bad enough to really need protection from. (LOL, for the mumps the main thing that happened is I took an afternoon nap - such an unusual thing for me that my mother took a picture.)
So, there you have it. Definitely don't auto-reject the idea of the flu shot over the presumed lack of effectiveness. Greater than 50% is actually a pretty good number in terms of people who don't get sick who might have otherwise, and the less than 50% who "get sick anyway" would have ... just that ... "got sick anyway". (It's like a seatbelt or a motorcycle helmet, in a way. Does the fact that some people still die with one on mean they're not effective? Not at all. They do save many lives. Even saying that, I'll still say no to the shot, but I do it knowing the risks involved and making a conscious choice to face them.)