Without change, something sleeps inside us, and seldom awakens. The sleeper must awaken. -Frank Herbert
Due to parachute failure, the Grace & Fury crashed on re-entry. It contained samples of toxoplasma erythraeum, which was later misnamed the exovirus. Containment proceedures failed. Close to 95% of the human population died within six months.
The United States government rapidly collapsed; Washington DC and Baltimore became police states, headed by a vice president intent on regaining control. New York City was placed under quarantine.
Almost a year after the outbreak, the Inturite Corporation released a cure. It wasn't cheap.
New York remained under quarantine for seven months; leaving required papers. Papers that were, like the cure, difficult to come by. During this time, the vice president shipped rations to the city. A handful of people, desperate to escape the city, lashed out at the soldiers that contained them.
The retaliation was brutal -- the next ration drops contained poisoned supplies. A week later, soldiers drove through the city, gunning down the survivors.
Civil war ensued, and a totalitarian regime followed, spearheaded by Caitlin Todd, of the Inturite Corporation. Zion emerged -- a tightly controlled city with a population that rivaled New York City at its peak.
Due to alleged mutations in the exovirus, the treatment was reengineered and released as Solcine. When it became evident that Solcine had addictive proporties, the Inturite Corporation further increased the price . . . as a deterrant to abuse, Todd claimed.
When new diseases occur (and they do, at a rate that keeps the population outside of Zion suppressed), the Inturite Corporation often provides treatment within a few months.