Different kinds of weapons deal different amounts of damage. While a non-armed combatant usually does no more than +0Harm, any kind of light or improvised weaponry deals +1Harm. If it's exceptionally heavy or well made, make this +2Harm. If both, +3Harm.
Harm is measured on a countdown clock, with the first harm taken equal to 3:00, the second one 6:00, then 9:00, 10:00, 11:00 and 12:00.
Harm before 6:00 heals automatically with time. Harm after 9:00 gets worse with time, unless stabilized. If the player marks the segment 11:00 to 12:00, it means that the character’s dead but can still be revived. Any harm past that and the character’s dead for reals.
At the end of each day, any harm past 9:00 automatically produces +1Harm unless Drugs were spend earlier to stabilize the patient.
Everytime a zombie hits a survivor, the GM may forfeit to inflict harm and infect the survivor instead. Each bite adds a segment to the Infection countdown of a survivor. Up to 6:00, he will show no visible symptoms. At 9:00, he is clearly and visibly infected. Unless treated with drugs daily, an infection will automatically worsen each day, eventually turning a survivor into a zombie after a maximum of 5 days without treatment.