The Infected are former humans who are the victims of the NEMEXIS virus, which has mutated them into zombie-like beings of their former selves.
They can no longer think or reason like normal human beings, causing them to become highly aggressive and homicidal.
The first Infected were born as a result of experimentation with a new stamina drug. An "accident" lead to several test subjects developing abnormal symptoms, augmenting their speed and stamina, but also causing them to lose their rational thought.
These mindless creatures began to attack the people working within LAB 3 and, coupled with their enhanced durability, quickly overwhelmed them.
Anyone who came in direct contact with the Infected (who had become carriers of the experimental drug) soon joined their ranks. Attempts to contain the outbreak failed, and the Infection quickly spread within LAB 3 and beyond.
The number of ways you can become Infected are varying. While it is assumed that the Infection is contracted through typical injuries, such as bites or scratches, no official method of contracting it has been confirmed.
Secondly, there doesn't seem to be a set amount of time from the initial point of Infection, to when the person becomes an Infected.
Lastly, there doesn't seem to be anyone who is entirely immune to the Infection; as even the Player is susceptible.
Then there is the matter of carriers, or people who have contracted the virus, but have yet to show any symptoms or changes.
Method of Transformation
Contraction through Bites
The Infected are rarely known to bite their victims in-game, despite doing so in the Quarantine Mode Trailer. The results are even more ambiguous as Viper, who was bitten by the Infected in the trailer, is killed before any notable changes take place.
Cabin Fever hints that the Infection can travel in liquids (or even the air) through limited means. The main character of Cabin Fever seems to have contracted the infection through the air.
The Striker further hints that protective gear (such as gas-masks) also offer little protection against the Infection.
The original test subjects, along with Mutagen-wielders, have shown that the most effective method of Infection is through direct injection; though with the Mutagens, the effect is delayed until one comes into contact with another Infected.
Duration of Transformation
During the events of Cabin Fever, the main character eventually becomes infected towards the end of the game.
Whereas in Quarantine, players "turn" in an instant. This also applies to those who use mutagens, where the effect is also instantaneous.
Degree of Transformation
The type of Infected that someone becomes is reliant on some unknown determinant. There is nothing to support why one person might become a normal Infected, while another becomes a Special Infected.
There is, however, a common trait among each individual type of Special Infected that they all share. For example, each Crusher is assumed to have been an individual of authority (such as the Crusher Captain) before they became Infected. All Chargers happen to wear a vest with dynamite attached to it.
With the use of Mutagens, players are able to become an Infected type of their choosing; Strikers or Crushers. This isn't to say that all Strikers and Crushers were caused by mutagens; but rather, mutagens were derived from their strain of Infection.
Because the virus originally stemmed from a drug, it may be considered as more of a biological contaminant (or even a pathogen) than a disease which brings the dead back to life.
While they have been officially referred to as "the walking dead" or even "zombies", the Infected may simply be living individuals.
- Have very noticeable changes in appearance and behavior.
- Have more endurance and stamina than a normal human; and can move very quickly.
- Have much more strength than any normal human.
- Suffer a major loss of cognitive skills; though their reasoning is gone, they still retain some of their intelligence.
- Suffer a major loss of vocal ability.
- Suffer a major lack of balance; most Infected are hunched, and some can easily be knocked-back.
- Have an increase in hearing ability.
- Have glowing eyes.
- Use their claws to attack; and can directly Infect other people.
- Have a general resistance to all damage, thanks to their skin.
- Have an immunity to:
- Are extremely resistant to:
- bullets in general; protection once ranged from near-immunity (0-4 damage max), to the current maximum (6-15 damage per bullet) after a series of updates.
- Are (slightly) more vulnerable to:
- melee attacks (though use of melee is discouraged)
- explosives and fire
(Main article: Host Infected)
Host Infected are a special type of Infected. Through the use of mutagens, these Infected are the original sources of the Infection. Because of their unique genetic make-up, and the fact that the Infection has had more time to completely bond with the Host, Host Infected have far more potential than the Viral Infected.
(Main article: Viral Infected)
Viral Infected consist of people who have contracted the virus through someone (or something) else. Direct contact (bites or scratches), and even prolonged exposure to the virus (Cabin Fever) are ways to become Viral Infected.
Viral Infected are more numerous than Host Infected, though they are weaker.
Despite their similarities, there are major differences between a Host and Viral Infected. Further mutations can be classified under these two categories.
- Have pallid, grey skin
- Have more power, health, and sprint stamina
- Have more "authority"
- Have better vision (with no damage to the eyes)
- Have normal camouflage (from a lack of injuries)
- Have fleshy, red skin
- Have a clouded, "bloody" vision
- Have a bloodier camouflage due to being covered in blisters and sores.
The first major mutation resulted in four different types of Special Infected; the Mauler, the Charger, the Striker, and the Crusher.
- Maulers are the weakest of the Infected, with no notable skills or abilities. However, to make up for their lack of power, they are the most common enemy NPC in the game. Their mutation has caused them to regain some of their human intelligence to put up blunt objects.
- Chargers are the most aggressive of the Infected. They will not hesitate to charge, and will detonate once they come within range of you.
- Strikers are the fastest of the Infected. They hit fast and hard, and their slim frame makes them difficult to target. Strikers drop explosive growths upon death.
- Crushers are the strongest of the Infected. They have the highest durability, attack range, and damage, but are very slow and large to compensate. Crushers release a toxic aura upon death.
- Assault Maulers
- Crusher Captain
A second major mutation resulted in even worse transformations among the Infected.
- Splicers have the farthest attack range of the Infected, and immobilize their prey with a paralyzing neurotoxin through each successive hit. Like the Crusher, they also release a toxic aura upon death; though a Splicer's is much larger, in comparison.
- The Infected have yet to be encountered in broad daylight. During gameplay, and in every trailer or cutscene, the Infected are have only been fought indoors, in the late evening, or night.
- They may resort to hiding underground while it is still bright out. An official statement also supports the theory that they are nocturnal, "But watch out! When the sun sets, the Infected roam..."
- Host Infected retain their base camo, but viral Infected have a "bloody camo", result of the injuries taken when infected.
- Some of the Infected leave a trail of bloody footprints wherever they go. This can be attributed to the fact that the blood vessels in the feet have expanded and burst, making the blood bleed out of the shoes onto the ground.
- In Overdose, there is some evidence of animal testing, meaning that humans may not have been the only test subjects. That may make it possible to have Infected types other than just humans later in the game.
- In the official Quarantine Mode Trailer, Viper gets eaten by the Infected. This may mean the Infected can eat after all. Not much known, however, if the Infected can eat anything else.
- Other than with their claws or other melee weapons, there is currently no other way for the Infected to attack and Infect. The Infected do not have long-range methods of attacking.
- You can find a Quarantine poster in Kill Creek at the Bravo respawn site, right before the train tunnel.
- The Infected seem to follow a given hierarchy, such as sending the strongest Infected only when necessary.
- A prototypical vaccine was developed within the confines of Sector 25. However, terrorists who hoped to sell the "vaccine" on the Black Market attacked the site. The "vaccine's" current fate is unknown.
- The Infected cannot pounce outside of any cinematics; they must be standing "straight" before they can leap.
- When a player is is lagging, loading, or D/C'ing from a game, their Infected form still wields whatever weapon is being currently held.
- As of the 3/3/10 patch, the Infected in Quarantine Regen have lower HP, but gained the ability to regenerate their HP. They can do this by simply standing still for 3 seconds. An Infected regains 10% of its health every second. Due to a recent patch, the Infected have lost their ability to regenerate. The newest patch allows them to regain 10% health again.
- The Quarantine Regen Crusher regains 20% health instead.
- It is possible for some people to lag out and spawn with infected hands, but the rest of their body is human.
- If the human is lagging with a weapon, when he/she is infected the infected soldier will be an infected with a weapon in their hand.
- Some Infected can "Play Dead", such as in the Combat Arms: Zombies trailer and in Dead Water.
- The NEMEXIS mercenaries encountered in NEMEXIS HQ and Labs can be seen to have glowing red eyes when viewed up close, revealing that they are on a 'refined' version of the Infected drug.