What is the chance of catching swine flu again, or are you kind of resistant to it once you have had it?

i had swine flu last october .three of my family members were given tammy flu tabs.i allso did a swab that was sent in the post randomly by some medical practice ,it turned out i was tested positive for the swine flu,can we catch it again.it was pretty scary i was quite ill with it,anyone know if me and my family members will of built up some kind if immunity cheers emma xxx