The Infected of Danny Boyle's film 28 Days Later are one of the earliest examples of the running zombie variant that has become increasingly popular in 21st century cinema. Aside from running, however, what really sets these creatures apart from traditional zombies is that they are not undead. They are still alive in every sense of the word, but have been driven into a state of perpetual homicidal rage, losing all reason and driven only to kill or infect any uninfected persons they encounter.
In the film 28 Days Later and its sequel 28 Weeks Later, the entire population of Great Britain has succumbed to a manmade disease known as the Rage virus. This infection was developed by military scientists who were trying to create an inhibitor to pacify violent criminals, but their work yielded opposite results. They had experimented on chimps, and one night, an animal rights group broke into the laboratory where the chimps were being kept. The activists released the chimps, unaware that they were infected, and the rabid chimps attacked everyone in the room and passed on the virus.
The Rage virus is carried in its victims' blood and saliva; those infected become completely aggressive to those around them, losing all powers of communication and reason and are driven by a senseless, irrational hatred of everything. Their irises turn red and they will attack any uninfected persons on sight. They have so much adrenaline running through their systems, they seem to ignore pain and injury and can run at an athletic level continuously without getting tired. While they lose most of their cognitive skills and cannot use complex devices, Infected can wield certain objects to club their victims to death. Otherwise, they just use their hands and teeth. Rage carriers also seem to produce an excess amount of blood in their bodies, which they will occasionally vomit up. This is their main method of infecting others; any blood that enters any bodily orifice will pass on the virus. The infection is rapid and subjects will become enraged in 28 seconds.
Infected are not zombies, at least not in the traditional sense. They are still alive in every sense of the word and can be killed in any way a normal human could be. While they tend to ignore pain, they have no sense of self-preservation and will not acknowledge any hazard or obstacle standing between them and their prey. Even so, fighting the Infected is foolhardy as they always seem to attack in large numbers. Because all their instincts are overshadowed by pure rage, the Infected do not notice or care if they are hungry and will eventually starve to death.