Killing of characters... zombies....?

You can trying adding a virus when a group of characters or few of them are in a room and all of a sudden green smoke appears and they start coughing. Slowly the end up trying into zombies. You can also have a needle that you inject that makes you a zombie. I get these from zombie movies and video games like Resident Evil. You can make the characters that survive only one of them that can not be a zombie because of this virus in them that blocks them from being one.