This (context) is most helpful, I think.
A couple of years ago my sister was diagnosed with multiple sclerosis. My brother and I did some research and learned that because she has it, each of us has about a 1 in 100 chance of being diagnosed with it at some point in our lifetime.
Sounds scary, huh?
Well, consider this: here in the US, we have about a 1 in 100 cumulative chance of being killed in a car accident:
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37K traffic fatalities per year
309M population
= 0.0001197 (1 in 8354) chance of being killed in any given calendar year
80-year lifespan
= 0.00958 (1 in 104) chance of being killed in a car accident over your lifetime
Of course, I’m a better-than-average driver (isn’t everybody? :D), so my odds are a bit lower, but it’s fair to say that death-by-car-accident and developing MS are in the same order of magnitude. I’ve never been particularly fearful of death-by-car-accident, so understanding that MS presents me with similar lifetime odds makes me feel better (about MS).
You are 100 times more likely to die in a car accident (not just be in an accident, but actually get killed) than you are to develop GBS.
If you think an incidence rate of 1 in 10,000 (flu sufferers who develop GBS) makes it “common,” what would you consider “uncommon?”
Consider a football game at the University of Michigan’s “Big House” stadium, which seats about 100,000 people. Give all of them the flu, and if your “1 in 10K” stat is correct, we could reasonably expect approximately ten of those football fans to develop GBS. That seems pretty uncommon to me. OTOH, given the flu’s mortality rate of 0.1%, we would expect approximately 100 of them to die.