A zombie bite infects you 100% of the time — there is no chance to survive one. A laceration infects 25% of the time, and a scratch 7%, on pzwiki’s default Blood and Saliva transmission setting. Those three numbers come from a single table on pzwiki’s own Knox Infection page, titled “Chance of transmission,” and they’re the only place in the game’s documentation where the odds are given as flat percentages rather than described in prose.
The transmission table, as pzwiki states it
| Injury | Probability |
|---|---|
| Scratched | 7% |
| Laceration | 25% |
| Bitten | 100% |
This table sits under a “Chance of transmission” heading pzwiki defines as “the chance the player will contract the disease, based on what injuries they have sustained from zombies.” It applies to the default Custom Sandbox transmission setting, Blood and Saliva — the setting every non-custom game mode uses. There’s no in-game UI that shows this table to the player directly; it comes only from the wiki page itself, built from community testing and datamining rather than a tooltip or patch note.
Two other rules bound the whole page. First, only zombie-inflicted wounds can ever trigger Knox Infection: “Any injuries that are not inflicted by zombies will never cause the player to get infected,” so a fall, a kitchen-knife accident or a car crash never rolls against this table no matter how bad the wound looks. Second, popular myths pzwiki explicitly debunks include the idea that zombies with visibly bloodied hands are more infectious through a scratch (they aren’t — blood on their hands usually just means they climbed through broken glass), and the idea that climbing through broken windows itself can infect you without a direct zombie attack (it can’t — regular wound infection can happen there, but not Knox Infection).
Why “25% for a laceration” undersells how dangerous zombies are
Lacerations and scratches are lower stakes per hit than a bite, but the real risk in a fight is that every connecting zombie hit rolls independently against this table. A single scratch is a 93% chance of nothing happening — but two scratches in the same fight bring your cumulative infection-free odds down to about 86%, and that keeps compounding with every additional hit you take. The table gives no indication that armor, clothing, or wound location change these specific percentages; what your gear changes is a separate question, covered below in what this page didn’t confirm.
What changes the time to death, not the odds of infection
Once you’re infected, two traits change how fast it kills you — not whether you got infected in the first place:
| Trait | Effect |
|---|---|
| Resilient | -25% zombification rate |
| Prone to Illness | +25% zombification rate |
pzwiki’s own symptom timeline (below) is the baseline these percentages modify. It runs on a fixed schedule from the moment of infection to death and reanimation:
| Time since infection | Symptom |
|---|---|
| Immediately | Rapid temperature increase |
| 1-4 hours | Anxiety |
| 5-12 hours | Queasy (stage 1): slight health loss |
| 13-24 hours | Nauseous (stage 2): moderate health loss |
| 25-48 hours | Sick (stage 3): severe health loss |
| 49-71 hours | Fever (stage 4): terminal damage |
| 72 hours | Death: zombified |
That default 72-hour window is itself only the default: Custom Sandbox’s “Infection Mortality” setting can stretch or compress it (Instant, 0-30 Seconds, 0-1 Minutes, 0-12 Hours, 2-3 Days default, 1-2 Weeks, or Never), independently of the Chance of transmission table above. “Never” means a chance to survive the disease itself once contracted — it does not mean the player can’t contract it.
The game never tells you directly that you’re infected. pzwiki notes the first real tell is stress and queasiness with rising body temperature appearing “within hours” of contracting it, and that if those symptoms show up for no other reason — especially right after a zombie encounter — “it is almost certainly the Knox Infection.” There’s no cure and no way to reverse the progression once started: not rest, not food, not disinfecting the wound after the fact.
The four Sandbox transmission settings
Custom Sandbox lets you change what can transmit the disease at all, in the Zombies tab:
| Setting | What can infect you |
|---|---|
| Blood and Saliva (default) | Scratches, lacerations, and bites — the 7%/25%/100% table above |
| Saliva Only | Bites only; scratches and lacerations can never infect |
| Everyone’s Infected | Anyone who dies reanimates, whether or not they were ever attacked by a zombie |
| None | The player can never contract Knox Infection, even from a bite |
Saliva Only is the setting that most directly targets the table above: it doesn’t change the 100% bite number, it just removes scratches and lacerations from being able to roll against the table at all.
The old “survivable bite” myth, and why it’s wrong now
pzwiki records that this wasn’t always true. In patch 0.1.6a, there was a small 4% chance to survive a zombie bite outright. That was removed in a later update, and a bite is now, per the page, “100% lethal” — matching the Chance of transmission table’s own 100% row. Players who recall surviving a bite are remembering a mechanic from a much older build, not something still active on 42.20.4.
What this page didn’t confirm
- Whether the 7%/25%/100% figures are rolled once per hit, or once per fight/attack sequence. pzwiki states the odds but not the exact trigger point in the game’s combat resolution.
- Whether Resilient and Prone to Illness affect only the time to symptoms and death, as the page’s own wording (“zombification rate”) suggests, or whether either trait has any secondary effect on the transmission-chance table itself — not stated on the page checked.
- Whether clothing’s scratch/bite defense percentages reduce these specific transmission odds, or only reduce the chance that a zombie attack connects as a wound at all before this table is ever consulted. Neither page checked states which.
Related reading
For unexplained health loss that turns out not to be Knox Infection — internal bleeding, untreated fractures, and other silent killers — see the cause-of-death diagnostic, which walks through the symptoms that look similar to the queasy/nauseous/sick stages above but come from a different source entirely. Corpse sickness (more than five bodies piled together) is another non-wound cause; see corpse pile cleanup and base placement.
Sources
- PZwiki, Knox Infection — read in full 22 September 2026. Chance of transmission table, Traits table, symptom timeline table, the four Sandbox Transmission settings, and the Popular myths section (including the 0.1.6a 4%-survival history). Page states it was last updated for 42.13.1; the stable build at the 22 September check was 42.20.4, and the 42.21 changelog lists no change to infection chances.
- PZwiki, Tailoring — cross-checked 17 September 2026 (via this site’s own Tailoring article) for the scratch/bite defense percentages referenced in Open questions. Does not mention the Chance of transmission table.
- Steam news, Project Zomboid news hub — checked 22 September 2026. Confirms “42.20.4 STABLE & 42.19.2 UNSTABLE & 41.78.21 LEGACY Hotfixes Released,” dated 26 August 2026, as the most recent stable release.
