Knox Infection

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“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 it began in the state of Kentucky, U.S.A, in the rural area of Muldraugh and West Point. 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). The Knox Infection began to spread throughout the area of Muldraugh and Kentucky, KY. The military set up a blockade around the affected area before it managed to spread further, 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, KY, 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, breaking down society, and even spreading across the ocean to Europe, Asia, and Africa.


The infection is known to only infect humans through bodily-fluid contact – such as bites and scratches – and at some point ‘evolved’, infecting those even without fluid contact. It takes up to three days for the infection to eventually kill its host, who will then be reanimated within an hour after death.


The pathophysiology of the infection is never mentioned during the events of Project Zomboid. 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 body’s counteractions are unknown.


There are people in the world that are rumored to be immune to the airborne strand of the virus, such as the player, yet are still capable of getting infected via bodily fluids.

It is not known if any people that are fully immune to the virus exist.

Game mechanics


The game won't immediately tell the player that they are infected, but instead slowly have more symptoms showing up.

  • Health loss from zombification can never be stopped and can only be slowed down by being Well-Fed and not being dehydrated and/or catching a cold.
  • The actual length for symptoms to appear and death are varies between players, and traits can also affect those.
    • Resilient - -25% zombification rate
    • Prone to Illness - +25% zombification rate
  • Immediately
    • Rapid Temperature rise
  • 1 - 4 hours
    • Anxiety
  • 5 - 12 hours
    • Queasy, 1st stage, slight health loss
  • 13 - 24 hours
    • Nauseous, 2nd stage, moderate health loss
  • 25 - 48 hours
    • Sick, 3rd stage, severe health loss
  • 49 - 71 hours
    • Fever, 4th stage, Terminal damage
  • 72 hours
    • Death, Zombified

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.

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 new characters to gather their processions without the Knox Infection overtaking their characters.
  • "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. The infection does not exist outside the body. Like some of the myths above, this may be due to regular infections on broken glass scratch/laceration wounds.


  • Infection lore is heavily based on George A. Romero zombies, with some very minor alterations.