Popular wisdom tells us that if you contract a disease or infection then your body develops an immunity to it by manufacturing antibodies for repelling that particular disease; so that you don’t usually catch the same thing twice.
According to this expert this acquired immunity will last typically for a couple of decades except in the case of those with compromised immune systems. For the most part this is true for the H1N1 Swine Flu virus as well.
With the current Swine flu virus though, the current strain is a new one that has elements of human, swine and bird flu viruses so in that sense it is a new virus and most people will have no immunity to it the first time around.
If one is infected now and the virus then once again mutates or changes, then that same virus in a changed form will have infected you again. This is one of the apprehensions that the medical community currently has about this current Swine Flu pandemic, that it will mutate and change form.
The bottom line is, that even if you have had the swine flu, you still need to be vigilant and careful about prevention. Continue to take the usual precautions of hand washing, sneezing into a napkin or the sleeve, staying home and not congregating indoors if you have symptoms.