Your post confuses me. You do realize that being healthy and fit is exactly the opposite of being in poor health, right?
Yes, but the effects on the immune system are not the exact opposite of each other. Basically, the immune system is not a muscle. If you are in poor health you will weaken that system, and returning to normal health will bring that system back to normal. But that's it. NORMAL. If you then decide to get all fit and healthy, your immune system does not grow with your muscles. It's as strong when you're extra healthy as it is if you are of average fitness. You can push it down, but not build it up. There are drugs that can do that temporarily. Oh, and vaccines do that, by adding to the number of antigens the system knows how to recognize and kill.
But being in better physical condition than average, or taking suppliments, or a special diet? No. Basically as long as nothing is acting to waeaken your immune system, it's running at it's natural pace, whatever that may be.
You also seem to have forgotten the fact that a healthy and fit person will fight of minor problems (things other than viruses) much easier and quicker than someone who isn't healthy. What does this mean? It means their immune system is freed up more than an unhealthy persons', ready to fight the flu.
One, it's how you define healthy and unhealthy. Being a overweight won't affect your immune system. In that regard, they're healthy as anyone else. Diabetes, OTOH can affect the immune system. If you have that you may not have a healthy immune system.
Two, Influenza is not a minor problem. Minor compared to cancer, maybe. It's a major challange to the immune system. Even for a big tough healthy person. It's hardest on the sick, weak, old, or young. But fit healthy adults die too. See, that's because their "sooped-up" immune systems FAILED. Even the regular seasonal flu kills tens of thousands of people every year. With vaccinations widely available.
I stay away from Purell (or whatever it is) for the same reason I stay away from flu shots. Viruses and bacteria evolve very quickly. So quickly, that when you put anti-bacterial crap on your hands, most of the bacteria is killed but the bacteria that survives has already evolved into something more dangerous than what you just killed. And guess what, this new bacteria basically just got a "Purell Shot" - making it immune to most anti-bacterial measures.
Vaccines do not work like anti-biotics. They don't kill the virus. It is quite impossible for vaccination to cause the evolution of a vaccine resistant strain. Because the vaccine never touches or interacts with the virus at all. Ever. It only interacts with the immune system. You don't vaccinate someone who has the virus already, you give it to someone BEFORE they get the virus.
The virus itself, through random mutation, may mutate into a form which the vaccine won't provide immunity to. The flu virus does that every year, always did, always will, no matter whether we vaccinate or not.
