Knox Infection

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Navigation: Main>The Game World>Gameplay>Knox InfectionPage updated: Version 41.65
This section is likely to contain major spoilers pertaining to the story of Project Zomboid.
“The Knox Infection's final stage is one of violence.”
— Kirsty Cormick
Knox Infection (commonly known as zombie infection) is a highly contagious disease contracted only by humans. This disease is very different from the common cold, food poisoning or wound infection. It is the main catalyst and antagonist for the events that unfold in Project Zomboid, dubbed the Knox Event.



Very little is known about the origin of the disease, other than that its first known outbreak began in the state of Kentucky, U.S.A, with the largest outbreaks specifically in the city of Louisville. There are several rumors about the origin, such as; misfolded prions in the meat of Spiffo's, terrorist attack, bioweapons testing gone wrong, and God's punishment for the sins of Man.

Initial outbreak

The exact date of the initial outbreak is unknown and estimated to be between July 2 and July 6, 1993 (one week prior to the start of the game, on standard settings). The military quickly set up an "exclusion zone" around Louisville before it managed to spread further, temporarily containing the outbreak. At first, the government portrayed the outbreak to be flu-like, causing panic and confusion among the infected. The infection is known to spread through fluid-contact: being scratches and bites.

Five days after the blockade went up, the WHO grounded all non-military or -medical international flights, which lead to mass panic throughout the nation and a disgruntled response from the President. The response and lack of clarity from the United States government led to international leaders condemning America, with the UK premier criticizing the President’s “near lack of clarity”. A photo from West Point is leaked out of the Exclusion Zone, with an image of a man covered in blood and bites, one arm missing, in a street crowded with dead.

Second wave

After 8 days, shots and explosions occur at the border of the exclusion zone, catching the attention of infected civilians, leading to hundreds, maybe thousands breaking through the blockade. Within two days, the infection spread North to Louisville, littering the streets in dead along the way. As a last resort, the military blew the bridges across the Ohio River, leaving those left in Louisville to fend for themselves.

Something is released with the wave of the dead, as people begin showing symptoms of the infection without coming into contact with any infected. The Knox Infection quickly spreads throughout the U.S.A, causing a breakdown of society, and even starts to spread across the ocean to Europe, Asia, and Africa despite the WHO's lockdown order on American flights.


Initially the infection seemed to only spread via fluids - typically blood and saliva - and thus transmission rate was relatively low. Approximately a week into the Knox Event however, it mutates and an airborne strain develops, which then spreads much more rapidly after the incident at the exclusion zone border and the breach thereof.


Those infected will suffer influenza-like symptoms for up to three days after contracting the illness, and eventually succumb - after which they will then reanimate within an hour after death.

The infection could also apparently be detected via blood tests.


The pathophysiology of the infection is never mentioned during the events of Project Zomboid, though radio interviews suggest that infected individuals become confused and fatigued prior to death and reanimation. However, it is likely of viral or prion origin, as it’s mentioned to be “flu-like” (virus) and Professor Peter Endsleigh draws a connection between Mad Cow disease (prion) and the fact that the infection is “clearly a neurological disorder”. There are no known cases of surviving the infection, and so therefore the direct effects and immune response (if any) are unknown.


Whilst select individuals (such as players) are immune to the airborne strain of the infection, there are no known cases of immunity of both, the airborne and the contact strains.

Game mechanics


The game will never outright tell the player that they are infected, and will instead develop symptoms over time. Although some radio broadcasts mention the infection can be diagnosed with a blood test, this is not currently a game mechanic. As symptoms worsen, the player's health will degrade faster, which cannot be stopped and can only be slowed by remaining well-fed, hydrated and absence of a cold.

Infection mechanics can be customized using custom sandbox settings, allowing for adjustments to the speed of mortality and delay before reanimation.


The time before symptom onset and death will vary between players, and is affected by some traits.

Icon Trait Effect
Trait resilient.png Resilient -25% zombification rate
Trait hypercondriac.png Prone to Illness +25% zombification rate


Time 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


Under standard game rules, characters who have contracted the Knox Infection will reanimate within a minute or two of their death, and will do so regardless of their actual cause of death.

Custom difficulty options can alter the amount of time before a deceased character reanimates, reducing it to as low as near-immediate or increasing it to as long as a one to two week delay. Another option can make it so that all characters carry a 'latent' or 'passive' strain of the virus which will cause them to reanimate upon death even if they did not contract the virus directly from a zombie.

Infection rate

It is only possible to contract the Knox infection by getting scratched, lacerated, or bitten by a zombie. The probability depends on the type of injury. Non-zombie related injuries will never result in contracting the infection, though they may result in conventional wound infections if not treated properly. Zombie scratches and lacerations can also become conventionally infected without contracting the Knox infection.

Transmission Probability
Scratch 7%
Laceration 25%
Bite 100%


The disabled hypochondriac trait will cause the player to occasionally get the symptoms of the zombie infection after receiving a scratch, without actually being infected. The progression is identical to the Knox Infection, however once the 'fake infection' reaches its peak, the infection will dissipate as the player begins to recover. The rate of recovery is much quicker than the infection's progression. However this trait is currently commented out (as of Build 41.65) and cannot be added to a character without being modded back in.

Popular myths

  • "There is a small chance to survive a zombie bite" - this is referring to a previous bug that resulted in a ~96% chance of surviving a zombie bite, and has since been fixed, making a zombie bite 100% lethal.
  • "It is possible to recover from the infection with enough sleep, food, and drink" - this may have been caused by the hypochondriac trait, general food sickness, or even confusion with wound infection. It is impossible to survive the 'real' infection.
  • "Disinfecting the wound immediately and regularly will destroy the infection" - this is not the case - once infected, there is no way to remove the infection.
  • "Dying before the infection kills you (drinking bleach), will stop your body from reanimating after death" - this is referring to a bug that existed in versions prior to Build 41.5. This bug/strategy allowed players to prevent reanimation and allowed players to collect their possessions without needing to track down and kill their zombified former character who may have wandered off.
  • "Zombies with blood on their hands are more likely to infect with scratches" - while this makes physiological sense, this is not the case. Zombies with bloody hands have usually climbed through a broken window.
  • "It is possible to get infected by climbing through a broken window without clearing the glass first" - the infection can only be contracted from being directly attacked by a zombie: it does not exist outside the body as far as the game's tracking of such is concerned. Like some of the myths above, this may be due to poorly-treated scratch/laceration wounds from broken glass.


  • Infection lore is heavily based on George A. Romero zombies, with some very minor alterations.
  • There is a secret government facility deep in the woods on the southern edge of the map which seems to have some medical and animal testing facilities and is a massive hotspot for the infected. Whether it is related to the outbreak or not is currently unknown.