A huge meteor strikes the earth out of the blue, causing global devastation as it sends clouds of dust high into the atmosphere and tremors that lead to widespread Tsunamis. In the aftermath of the impact, an even greater threat to humanity emerges as a virus carried upon the meteor tears through the survivors in the area around its impact.
The virus (later named Helminthian Virus after the latin term Helminth for parasitic worms) attacks human brain tissue, burrowing random tunnels through the brain. In some people the damage is so extensive that they die within days, in others it leaves them helpless and immobile, but for many it destroys areas of the brain that provide control and reason. The result is a mass of people who act like wild animals, motivated only by base instincts and fragments of who they used to be.
For some their memory is lost, for others they retain skillsets and identities with their former self, but are now totally different people, in some cases murderous and cannibalistic, in other cases unable to use speech or recognise themselves as human.
The virus creates a disjointed world of lone survivors, loose packs of people with similar damage, zombie like masses and a few who have immunity to the virus that leaves them stranded in a post-apocalyptic world trying to find a solution.