Go on Wiki and put the words "Spanish Flu" in the search string. It will explain to you why the Swine Flu is of concern.
As I mentioned before, there is little news of mutation, so today it's a Flu as far as I know. Very catchy, but just a flu. But the 1918 one was very related and this is what happened:
"The second wave of the 1918 pandemic was much deadlier than the first. The first wave had resembled typical flu epidemics; those most at risk were the sick and elderly, while younger, healthier people recovered easily. But in August, when the second wave began in France, Sierra Leone and the United States,[41] the virus had mutated to a much deadlier form. This has been attributed to the circumstances of the First World War.[42] In civilian life evolutionary pressures favour a mild strain: those who get really sick stay home, and those mildly ill continue with their lives, go to work and go shopping, preferentially spreading the mild strain. In the trenches the evolutionary pressures were reversed: soldiers with a mild strain remained where they were, while the severely ill were sent on crowded trains to crowded field hospitals, spreading the deadlier virus. So the second wave began and flu quickly spread around the world again.[43] It was the same flu, in that most of those who recovered from first-wave infections were immune, but it was now far more deadly, and the most vulnerable people were those who were like the soldiers in the trenches—young, otherwise healthy adults.[44] Consequently, during modern pandemics, health officials pay attention when the virus reaches places with social upheaval, looking for deadlier strains of the virus.[43]"
The ones who already had it are the lucky ones, for the immunity is there. Another way to get immunity is by vaccination, which will strain your immune system, just not as much as the flu. This is how it works.
I must say, I am baffled by the hostile attitude against vaccination in general on this board, and cannot explain it with any other term than sheer ignorance.
Oh, by the way, we do have a biologist on this board. Biology is also a hobby of mine, as well as diagnosis of various diseases as well as vaccinations of lifestock is a part of my job.
We covered pox here. How many of you bitten by a rabid dog would take the chance and decline treatment. (rabis shot is basically a vaccination since it will give the body an immediate respond for a threat that comes later). Ready to try your luck on that one?