I'm guessing you'll start hearing this one any day now.  I first heard this claim a few years ago, after my school sent out an email offering free flu shots to students.  That was well before swine flu dominated headlines and the vaccine-autism manufactroversy dominated skepticism, so it seems like the stage is set for this claim to make a huge comeback.

A Kernel of Truth …

The danger this claim refers to is from the autoimmune disorder Guillain-Barré Syndrome (GBS).  GBS is a real but rare (1-2 per 100,000 people) disorder that can indeed be triggered by immunization, thus slightly distinguishing this week's statement from the usual antivax nonsense.  The precise cause of GBS is unknown, but symptoms typically occur soon after an infection.  Flu shots are known to cause GBS, with roughly one in a million vaccinations resulting in the disorder.

GBS occurs when your immune system mistakenly attacks part of your own nerve cells rather than a target foreign pathogen.  The outer layers of the nerves are damaged, resulting in weakness and numbness that spreads throughout the body.  GBS is a serious disorder, requiring hospitalization and rather intense monitoring and treatment.  An estimated 3-4% of cases result in death, but it is thought that most deaths are due to inadequate or nonexistent treatment.  Prognosis is generally good, with about 80% of patients recovering fully.  Still, 5-10% of patients are permanently disabled by the disease, making GBS one of the most common non-trauma-induced causes of paralysis.

… Popped Entirely Out of Proportion

Although GBS is indeed real (and pretty darn ominous), it shouldn't scare anybody away from getting the flu vaccine.  Any medical procedure carries risk; after all, the puncture wound from the injection might later get infected and kill you.  As always, you have to consider the relative risks.  Over thirty thousand people die from the flu in a good year in America, making your overall odds of dying from the flu in a given year about one in ten thousand.  These odds are low, but they aren't zero.

Of course, the situation is certainly more complicated than this.  Healthy adults are much less likely to die from the flu than the elderly or infirm; on the other hand, infected healthy adults might spread influenza to highly susceptible people they interact with.  Being sick for a week or so might sound better than chancing GBS via vaccination, but then again a regular influenza infection also puts you at risk for developing GBS.  The flu vaccine contains thimerosal, but the furor over that preservative is pure antivax propaganda.  A given year's vaccine doesn't protect against all the extant influenza strains, but they're pretty good about forecasting the most prevalent type.

The last complicating factor is that the 1976 swine flu vaccine resulted in GBS much more often than other flu vaccines.  An outbreak of swine flu at Fort Dix killed an army recruit, and fear of a pandemic like the 1918 Spanish flu led to the government rushing to immunize the entire country against this swine flu.  The pandemic fizzled, and moreover vaccination resulted in GBS at a significantly increased rate: ten cases per million vaccinations (rather than one per million).  We do not know if this increased rate is something inherent to swine flu vaccines, or if it was a fluke possibly exacerbated by the vaccine being rushed.

Despite these complicating factors, getting the flu vaccine is a net positive.  The odds of an adverse reaction to the vaccine are extremely low, and your immunity may prevent your or your loved ones' disease or death.

Odds and Ends

While we're talking odds, I think that odds are someone professing this week's statement has just picked up and passed along an antivax factoid.  As bad as GBS sounds, one-in-a-million odds are worse than the odds of being struck by lightning in a given year (1 in 700,000).  People tend to be terrible at judging relative risks.  Parents live in fear of a stranger abducting their children; in reality, a child is much more likely to drown in a neighbor's pool than to be kidnapped and murdered.  You have to look at these things objectively, because mundane-sounding deaths are no less deadly than spectacular-sounding deaths.

Any way you slice it, the risk you take getting the flu vaccine is lower than the risk of getting the flu itself.  That's to say nothing of herd immunity considerations; every strain of flu you're immune to is one you cannot spread to someone else.  Flu vaccines aren't compulsory, so you need to decide for yourselves whether or not to get vaccinated.  Just be sure that your decision is based in reality, and not misinformation or misunderstood statistics.