ZN1 is the Center for Disease Control (CDC) designation for the undead-creating virus that is responsible for the global zombie apocalypse.
Very little is known - or at least widely known - about its origins.
The first case of infection known was in the year 2016, as mentioned by Murphy in Doctor of the Dead.
Symptoms of ZN1 include, but are not limited to:
- Damaged nervous system with limited cognitive activity.
- Violent tendencies towards non-infected individuals.
- Acute sensing, visual and auditory range, of non-infected individuals or repetitive sounds.
- Physical abillites are both enhanced and debilitated, victims having almost limitless endurance, although their muscles have been deteriorated.
- Increased resistance to traumatic physical injury except to the head/brain.
- Head and brain trauma are the only things that will kill a ZN1 victim.
ZN1 is transmitted through bite, leading to a rapid transition to a zombie, or after a non-zombie individual dies, leading most people to realize that everyone is infected.
The only known survivor of direct contact is an involuntary test subject from the Portsmouth Naval Prison's infection control laboratory.
Murphy was injected with an experimental vaccine, which - unlike previous versions tested on other inmates - did not turn him into a zombie. He was then bitten 8 times by infected and zombified individuals, again not contracting the virus.
It is believed that he holds the key to mankind's salvation in the form of antibodies his immune system formed as a result of his exposure to the vaccine. Operation Bite-mark was then established in order to deliver him to the CDC research facility at Mount Wilson Station in California - at all costs.
There was an experimental herbal vaccine being developed in a weed lab in Minneapolis, labeled Batch 47, which showed promise. However, when tested on a human, it proved lethal.
Blends created by Murphy are both ignored by those infected with ZN1 and are immune to the virus, although this cure does carry the side effect of Murphy being able to control your actions.
Zona was able to cure ZN1, but their immunity began to fail, after which they sought out Murphy and his daughter, Lucy, hoping to use their antibodies to cure themselves. They succeeded, although a contaminant in Murphy's blood caused them to contract a degenerative brain disease, and they are all likely dead.
In Season 4 of Z Nation, the virus appears to have mutated, creating a type of Z which cannot be slain through conventional means, and must be almost completely destroyed before it will stop.