Don’t know. You don’t see any zombies’ gaping skin cuts healing up. If anything you’d think when your immune system gets weaker from overuse/can’t recharge under constantly fighting off an infection it can’t kill off, then you stress the body further with a bad injury, it should allow the virus to potentially take over - just like a bad chest cold or flu can allow pneumonia to set in as a secondary infection.
I’m not talking about the zombies. I’m referring to the still non-zombies who are already infected (according to Jenner’s whisper). As I said the reason is probably sloppy writing, which is endemic in this show, but the idea is that if the virus has the ability to reanimate the dead, then maybe it can also speed recovery in the living.