January 2017 an asteroid is detected on a collision course with Earth. Thankfully, the brains at NASA and various other international space agencies collaborated on plan to destroy the object by launching a craft with a nuclear payload aboard. Though it was a close call, the mission was deemed a success: upon detonation, the NEO broke up into smaller fragments that would disintegrate in the atmosphere, causing minimal impact on the Earth. On the ground, people celebrated under a glittering meteor shower. While most of the debris burned up, a few chunks remained intact. One bolide even managed to flatten a small town in Wyoming.

march 2017 A mysterious pandemic breaks out in several major cities, burning through "first world" nations first, then going global. the disease affects all age groups, causing fever, rash and intense pain, among other symptoms, for several days before killing the infected. while it wasn't fatal to everyone who made contact with it, replicating the natural resistance certain individuals possessed seemed close to impossible. Populations were decimated worldwide, with rioters and dissidents taking advantage of the chaos. governments were crippled, borders were closed and nations entered a state of emergency as they struggled to deal with the crisis.

june 2017 Just when we thought we were at our lowest, the Monsters began to appear. after months of study, the virus was revealed to be a parasitic spore that had hitched a ride on the asteroid. scientists worked around the clock to develop a vaccine; however, the attempt at inoculating humans against the disease only made it more aggressive. the newly mutated strand turned the infected into mindless 'undead' hosts, their brains and bodies hijacked by the parasites, attacking the living. the collapse of society seemed to happen almost overnight, weakened cities overrun, some areas bombed in futile attempts at stopping the infection.

present day months after the cataclysmic events that shook the world apart, survivors continue to endure with limited supplies against the natural elements, and the near constant threat of predatory zombies. not to mention the danger of other unpredictable, self-serving humans. while no place seems truly safe these days, rumors persist of stable pocket settlements scattered throughout the countryside, and even as far as the west coast. though it almost sounds too good to be true, banding together and finding sanctuary may be the only way for humanity to avoid extinction.
the infected are the disastrous result of human tampering, leading to a second deadly wave of the alien virus. those who had survived the first pandemic fell became vulnerable to a new strain that not only killed the host, but took over their body shortly after. the infected feel no fear or pain, only hunger for raw flesh, driven to propagate the parasite species by spreading to new victims via bite. even those recently dead through other causes may be carriers of the virus, and can be 'resurrected' by the parasite. so far, only humans have proven suitable hosts; most other animals tend to instinctively avoid the new apex predator. they may not be stopped by anything short of instant brain death or dismemberment. whether anyone retains natural immunity to the infection is unknown. the results of initial studies conducted by scientists on the infected did not reach the mass public before the collapse of the government. however, several stages of development have been identified as such:

STAGE ONE: RUNNERS develop within 2-3 days of infection. at the beginning of this stage, the host is still technically alive, but they rapidly lose all cognizance and sense of self after a week. the virus attacks the brain and nervous system, affecting eyesight, motor function, and mood, increasing hostility towards others. because they are lacking in coordination and move sluggishly, runners are easy to evade. however, when provoked, their aggression is relentless, attacking their target in an attempt to infect with a bite or tear them apart.
STAGE TWO: STALKERS usually develop 3 weeks after the first stage, and 4-6 weeks from infection. they are no longer considered "alive", and the host body has been entirely hijacked by the virus and has begun to undergo physical transformation. stalkers have increased speed, agility, and strength compared to the previous stage; their nicknamed is derived from their ability to track victims in dark environments through psuedo-echolocation, and a heightened sense of smell.
STAGE THREE: CLICKERS can develop anywhere between 2 to 6 months after stage 2 (or 3 to 7 months from infection). their physical mutations have developed to the point of complete physical blindness, but their other senses have been enhanced tenfold to compensate. they are much stronger and durable than the average human, and primarily track through echolocation, emitting screeching/clicking noises (hence the nickname). they are highly aggressive, and their heads are better protected than in earlier stages, requiring smarter tactics. thankfully, they are fairly uncommon.
STAGE FOUR: UNKNOWN have yet to be seen by anyone on record, but many believe stage 3 is not the final form of these horrific monsters.