So while I was doing my dishes today I was listening to today's installment of Scott Adams' morning podcast I don't listen to it often but when I do he often has some interesting insights to share. Apparently he has recently stirred up a small controversy by questioning the legitimacy of the annual flu death rate for basically as long as we've been recording that. Scott Adams never made any actual claims on this topic (nor will I) he was just asking questions as any good skeptic should.
One interesting idea that he brought forth was the idea of a Bubble Boy. A Bubble Boy is a kid raised in a sterile environment where he has has little contact with anything with germs, his house and toys are always kept clean and he is fed a "safe and healthy" diet. Because Bubble Boy was raised in a mostly sterile environment there is not much of a need for his immune system to fully develop so it doesn't and is thus weak and compromised (much like that of an elderly person for whom this sort of analogy could also be applied).
As long as Bubble Boy stays within the sterile environment that he was brought up in he will be fine, but this is impossible of course because he will inevitably have to join the outside world at some point and when he does he will be exposed to plenty of germs and viruses that he would not have been around before. Let's say that when Bubble Boy travels into the outside world he catches a common and uncontroversial virus that nearly everybody Bubble Boy's age would easily recover from like the flu. When this happens Bubble Boy will be in trouble, his immune system is simply not up to the task of fighting the flu since it has never been exposed to anything like it, Bubble Boy will be at risk of dying.
So the question behind this thought experiment is: If Bubble Boy were to die from this what is it that would have actually killed him? Was it the flu? Or was it the failure of his weak immune system?