My mind went drifting to day during class, and near the end of the day, I started thinking about Walking Dead, so here me out on this one.
The series takes place roughly a month after Rick was shot. Shane went to visit him in the hospital, from what I can tell, roughly a week to two weeks after he was shot and before Rick finds the Atlanta survivors. While he was in the hospital, his Heart stopped and the machines keeping him alive went off. So in all logic, he died. But he wakes up two weeks later and is alive and well, so heres what I think.
If we are to believe that everyone on the planet carries the virus, then Rick would to. When he died, the virus should have brought him back as a walker, but it didn't. Instead, he was given a second chance at life, and has been living his life ever since. From this, it would seem like Rick is immune, or at least his body fights off the virus better, or even processes it better since instead of only re-activating the stem it re-activated his brain.
I know this is confusing, but thoughts?