Surviving the apocalypse as a half zombie

After the outbreak of the x virus, the world has been turned upside down as zombies had now taken over the world killing more than half of the population in the entire world. Xavier is a 18 year old boy trying his hardest to survive with his older sister and comrades but when he was deemed too weak to be of any use the same people he fought besides betrayed him with a knife through his chest and abandoned him for dead. So how the hell was he still alive . His organs had completely stopped working but he was still alive and why was there a small child here claiming that she's immune to the virus. Xavier along with this strange little girl goes on a journey to find his sister and beat the hell out of the assholes who killed him.