On Friday, 5 January 2018 at 06:20:54 UTC, Patrick Schluter wrote:
The only people I ever saw with a flu (I mean a real influenza) had all one thing in common: they all had gotten the flu shot.
That's a case of selection bias: the people who get the shot tend to be those who are already at high risk of getting the flu.
The shots cover common strains - or at least what they think will be common strains - but they don't cover all of them. So consider the math: let's say you judge yourself to have a 20% chance of getting the flu, so you get the shot. It cuts your odds by about 50%... but that still leaves you with a 10% chance of getting one of the other strains.
The general population, on average, has about a 5% chance of catching the flu... so even with the shot, you, in the very high-risk pool to begin with, are still more likely to get it than the average person, but that doesn't mean the shot was ineffective, and, of course, it certainly doesn't mean the shot CAUSED it.
