In some stories, victims of zombies may become zombies themselves if they are bitten by zombies or if a zombie-creating virus travels by air, sexually, or by water; in others, everyone who dies, whatever the cause, becomes one of the undead. In some cases, parasitic organisms can cause zombification by killing their hosts and reanimating their corpses, though some argue that this is not a true zombie. In the latter scenario zombies also prey on the living and their bite causes an infection that kills. In either scenario, this causes the outbreak to become an exponentially growing crisis: the spreading “zombie plague” swamps law enforcement organizations, the military as well as health care services leading to the panicked collapse of civil society until only isolated pockets of survivors remain. Basic services such as piped water supplies and electrical power shut down, mainstream mass media cease broadcasting and the national government of affected countries collapses or goes into hiding. The survivors usually begin scavenging for food, weapons and other supplies in a world reduced to a mostly pre-industrial hostile wilderness. There is usually a ‘safe zone’ where the non-infected can seek refuge and begin a new era.
An early inspirational work of the genre was Richard Matheson‘s novel I Am Legend (1954), which featured a lone survivor named Robert Neville waging a war against a human population transformed into vampires. The novel has been adapted into several screenplays, including The Last Man on Earth (1964), starring Vincent Price, and The Omega Man (1971), starring Charlton Heston. A 2007 film version also titled I Am Legend starred Will Smith, in a more contemporary setting. George A. Romero began the idea with his apocalyptic feature Night of the Living Dead (1968) from Matheson, but substituted vampires with shuffling ghouls, identified after its release as zombies.
The literary subtext of a zombie apocalypse is usually that civilization is inherently fragile in the face of truly unprecedented threats and that most individuals cannot be relied upon to support the greater good if the personal cost becomes too high. The narrative of a zombie apocalypse carries strong connections to the turbulent social landscape of the United States in the 1960s when the originator of this genre, the film Night of the Living Dead, was first created. Many also feel that zombies allow people to deal with their own anxiety about the end of the world. Kim Paffenroth notes that “more than any other monster, zombies are fully and literally apocalyptic … they signal the end of the world as we have known it.”