It can be handled one of two ways! The first way is that the Green can simply cure him of the disease magically. The second way, if you want to play with the zombie virus as an element, is he can awaken in the game with an amulet or charmed piece of jewelry that suppresses the virus and prevents the virus's spread. In the latter case, he can be told by the voices that speak during the welcome sequence what the amulet is for.