Vanessa's abilities : bite and blood (spoilers for all Season 1)
Vanessa can turn vampires back to humans. Thanks to Doc's foolishness, we know that these people are now immune to bites and can't be turned into vamp again.
But what about the "guy in the freezer" from episode 2 ? This one : https://s24.postimg.org/5bsdu50cl/PSX_20161205_012800.jpg
He was the first vampire to turn, thanks to Vanessa's blood donation at the clinic. Given that he was still alive despite missing limbs and organs, there's more than bite immunity to Vanessa's abilities.
We now know that Vampires age and eventually die. So what's the deal with this guy ? He obviously wasn't dying.
Among the vampires turned by Vanessa, we have those who drank her blood (Flesh and the "guy in the freezer") and those she bit (Doc, Susan and Theo, human) Are all these characters as "death-proof" as the mutilated guy ? Susan surely wasn't death proof (unless she was buried alive). Only those who drunk Vanessa's blood ?
This leads to another question. Is Vanessa simply turning vampires back to their original nature, or is she actually turning them into something new entirely ?