The infected is normally a game where he must survive the hordes of zombies. I allow myself to change these rules: when starting a game, a countdown begins: you have to hide! At the end of this time, two players are randomly chosen to become Zombies. A new countdown begins, this one times the duration of the game. The goal then becomes, for the Zombies, to contaminate all the other players (These will become the infected) and for the Survivors to simply stay safe and sound.
