Rage (fictional virus)
Rage is a fictional virus appearing in the 2002 film 28 Days Later directed by Danny Boyle, and in the 2007 film 28 Weeks Later directed by Juan Carlos Fresnadillo. It also appears in the graphic novel 28 Days Later: The Aftermath.

# Characteristics
In the graphic novel 28 Days Later: The Aftermath, Rage begins as a genetically engineered strain of the Ebola virus designed to carry an unspecified treatment to inhibit violent impulses. However, instead of inhibiting violent impulses it has the opposite effect, causing the infected to engage in extreme violent behavior. This is likely because the original virus mutated into this form through a very quick form of evolution so the virus can remain constantly active. The virus is released into the population of the United Kingdom accidentally, shown as the beginning of 28 Days Later, when animal rights activists break into the lab where the infected chimpanzees are housed. It rapidly spreads to the general population.
Rage is used within the storyline of 28 Days Later and the related media as a scientific alternative to the zombie epidemics of various other film and media. The primary difference of Rage being that it does not kill or reanimate those infected, nor do the infected try to eat the uninfected (they bite to attack, not to eat, and the vomiting is a reflex action). Used as a plot device the effect is very similar - creating an army of mindless killers who will stop at nothing to kill any survivors of the epidemic. Unlike most zombies in popular culture the infected characters do not suffer any loss of motor control and can still move very quickly and climb obstacles. They can also be killed by any normal means or operate systems of access, as seen in 28 Weeks Later.
The virus is sometimes shown as being passed by the carrier vomiting blood in the face of the victim, causing the virus in their blood to enter the victim. The infected bite as they attack, spreading the virus, and any contact with a carrier's bodily fluids will also infect - Don in 28 Weeks Later is infected during a kiss from his wife. The virus seems to affect within 10-20 seconds after entering the blood although this varies. The virus is shown as 100% communicable and in the currently released films and graphic novel there is no known cure.  In supplemental materials on the 28 Days Later DVD, director Danny Boyle mentions using a complete blood transfusion in one of the alternate endings as a potential cure, but the idea was rejected by himself and movie crew due to not being credible.
Danny Boyle has stated that primates are the only animals that can carry the virus (a fact that is further touched upon in the second film in the series).

# Symptoms
The infected characters experience spasms in the extremities, and their irises and sclera become blood red. They also vomit copious amounts of infected blood and scream incoherently when they attack.
The Rage virus does not directly cause the death of its host, but because the Infected are solely focused on infecting or killing the non-Infected, they do not eat and eventually die of starvation. Since the Infected act with no regard for self-preservation, they will not act to evade mortal danger, such as fire or bullets.
The Infected will disregard each other and only attack those who do not show symptoms of infection. This is similar to the classic Romero-style zombies, who attack only the living. As a plot device, this allows for huge hordes of the Infected to hunt down a few lone survivors, and allows the virus to spread at an exponential rate through any group of people. According to 28 Days Later: The Aftermath, the Infected have a heightened sense of smell that can detect the odors associated with emotions. The Infected smell varied emotion in non-Infected, but they only smell intense rage in each other. This seems to be a matter of the infected recognising the symptoms of the virus rather than the presence of the virus itself, since Don Harris attacks his wife Alice when he becomes infected, despite the fact that she is a carrier of the virus (see below).
Though not widely covered in the films, it is obvious that some Infected retain a measure of intelligence.  There are only four cases within the films that prove this: the infected boy in the diner who shouts, "I hate you!" at Jim (however this may simply be the soundtrack for the scene being louder than others, as a number of other Infected attacks have similar cries in the background), and infected soldier Mailer who acts like he is injured and needs help in order to lure Jim close enough to attack. Also, when Jim frees Mailer, Mailer ran into the mansion in attempt to kill the soldiers instead of trying to kill Jim, though this could have just been Mailer going to find Jim but instead finding the soldiers. Also, when the group fled from the Infected in a cab in the underground road tunnel, the Infected stopped giving chase, knowing that they weren't fast enough to catch up.

## Don
Don, the main infected character of the second film, appears to retain the most intelligence. Examples of this include Don having a flashback of happy memories with his family, Don's ability to use objects as melee weapons, and attacking Tammy, Andy, and Scarlett from the darkness. Also, unlike other Infected, Don showed a sense of self-preservation. He followed the group around, but never attacked, knowing that he would be shot by Doyle. He also hid when District 1 was firebombed, as well as hiding from the chemical gas attack on the city, avoiding death twice.
One other example, though very brief, is how Don moves within the darkness of the subway; he is vaguely detected by the night vision scope on Scarlett's rifle, seen walking cautiously while Scarlett calls out for Tammy and Andy. This contrasts with how those infected with Rage move with frequent bursts of speed accompanied by vocalisations.

# Immunity/Carriers
28 Weeks Later explores the discovery that there are certain people that will not display any symptoms of the virus with the only symptom they manifest being partially red sclera. The film also suggests that a sign of immunity is heterochromia. These people are classified as "asymptomatic carrier". The person will not become uncontrollably violent like other Infected, and retain their normal personality. The person is not immune to the virus, however, just the symptoms, and the person can spread the virus as easily as any other Infected (such as saliva contact) in a manner similar to the real-life case of Typhoid Mary.