Kalavirus

Kalavirus, also referred to in the scientific community as M5-10, is a plague that kills ninety-eight percent of the world population. Although not released directly by the Army of the 12 Monkeys, their guiding hand and influence in its creation and release is undeniable. The Kalavirus poses significance to the Army of the 12 Monkeys because its release is the catalyst for the creation of Project Splinter, which plays a significant role in helping them achieve their ultimate goal of destroying time.

894
Olivia Kirschner's upper half is violently splintered back to the Himalayas in 894. Her remains would become the Annapurna Remains, resting there for over a thousand years before being discovered in the mid 1980s.

1987
Leland Goines purchases the remains after learning from Cole that it contains a virus. In the years following, Markridge begins to engineer the virus from the corpse.

2015
The virus is engineered by Oliver Peters. Soon, the Central Intelligence Agency contracts Markridge to weaponize the virus in the hopes of using it to kill Adam Wexler, who is hiding in Chechnya. The virus is transported in an attaché case containing money in the hands of a courier supposedly trusted by Wexler. Before Wexler and his associates can escape the compound and spread the virus, the CIA bombs the compound under the advice of Cassie. In an alternate timeline where Cassie is killed prior to the operation, the virus is released onto the world a year early.

Later, Oliver Peters is kidnapped by the Army of the 12 Monkeys, who force him to reconstitute the virus for them by threatening to kill his husband. Peters told Cassie that this variant of the virus was even more virulent than the original M5-10.

After Jennifer Goines becomes the CEO of Markridge, she is influenced by Olivia and the 12 Monkeys. Under their guidance, Jennifer soon decides to travel to twelve cities across the world with the virus in tow.

2016
On the day of the Chinese New Year, Jennifer unleashes the virus. From 2044, Cassie and Jones discover that this is the moment that would destroy the world. Cassie travels back in time to kill Jennifer. After a confrontation with Cole, they soon convince Jennifer to allow them to burn her entire supply of the virus. This changes the timeline and delays the release of the virus.

Post-Release of the Virus (2017 and 2018)
Prior to altering the timeline, the plague reached its climax in 2017. Quarantine zones are established throughout the United States, including the West VII Quarantine Zone. Chaos breaks out. After altering the timeline, the virus is delayed until 2018, saving millions of lives and providing Jones and her team with hope. In both variations of the timeline, Cassie works with the CDC to try and find a cure. She ultimately leaves a recording for Cole before dying.

2043
By 2043, 98% of the population has been wiped out. Civilization has collapsed and many groups of scavengers have been established to fend for themselves.

Symptoms/Pathology
The virus is highly contagious, spreading via airborne contagion and by direct contact with the infected. Symptoms included cough, fever, chills and aches, headache, fatigue, nausea, breathing difficulties, respiratory arrest, internal bleeding, and organ failure. The fatality rate among the infected was over 95%. As of 2017, there was no known cure or vaccine, although Jonathan Foster did apparently manage to cure some later mutations of the virus in 2043.

Strains
The Kalavirus mutated constantly into new strains. As of 2043, four strains had been identified:
 * The first strain (2016) killed seven billion people; fewer than two percent of the population (148 million people) were immune.
 * The second strain (2033) killed more than half of the survivors of the first strain; fewer than 59 million people survived.
 * The third strain (2037) killed a quarter of those who survived the second strain; fewer than 44 million survived.
 * The fourth strain (2040) killed thirty-five percent of those who survived the third strain; fewer than 28 million survived.

In 2016, Cassie, Ramse, and Cole stop Jennifer from releasing the virus. They then burn all of the vials in her plane. This alters the timeline and delays the initial release of the virus until 2018. It is unclear how the virus mutated following this change to the timeline.