Yes, if the strain mutates you could. Or if you are exposed to a different strain, there are many, you could. Hopefully your immune system recognizes the virus and produces antibodies that fight it the second time. Even slight coverage could be helpful.
As far as H1N1 goes medical experts say if the H1N1 virus behaves like the seasonal flu bug, those who've already been sick, should have immunity. But really, who knows at this point.