I haven’t read all of the comic books, but based on AMC’s The Walking Dead, when Shane came to get Rick out of the Hospital, Rick’s heart stopped beating.
Now Shane is a silly man, with a silly brain, I understand. However in those days his intentions were genuine. He checked for any sign of life from Rick, and there was none.
If his heart did stop, why didn’t he turn then and there. How long was it before he was revived? And by what?
Could it be that he’s immune to the virus? That the answer for a cure could be in him? - that would be too theatrical if it were. But since we’re already following his journey, he might be more than just a random survivor of the zombie apocalypse.