It doesn't bother you yet. Wait until you are say sixty or seventy years old. I am of course making a few assumptions here 8) Flu rarely kills young 'uns in reasonable to good shape with no other indicators or whatever doctors call it. I mean risks associated with a particular individual.

The point of vaccines is not perfection but more like a war of attrition. A vaccine has several potential purposes, some of them are these:

  * Reduce the possibility of infection
  * Reduce the effects of an infection 
  * Reduce the infectiousness of an individual to other people

The first two effects affect you personally and the third one affects society as a whole. The third one is the thing behind the "Don't kill grandma" meme. Your comment implies to me that you may not have considered it. If you have and are happy with that, then that is your prerogative.

Each of those items above have various probabilities associated with them and rather a lot of external factors and so on. A vaccine's stated effectiveness in each area will obviously be some sort of average across a population.

That's the thing: Vaccines inoculate societies as a whole and not just individuals when you look at statistics. The phrase "anecdotes are not data" is particularly true here.

Even a "lol sad" 40% effective (whatever that means) vaccine will slow the spread of the thing across a population and reduce the possibility of individual deaths or other non optimal outcomes. When you start to look at the population as a whole you see huge numbers of people living instead of dying.

With luck, one of those survivors might be you or me one day. This is the only time I will advocate a sort of communist approach to things. By "risking" inoculation, you reduce the possibility that someone else might catch the disease. You also get some additional abilities to fight off the bloody thing too - nice!