Pilot
It was just six or seven months ago when people started getting sick. Well, at least that's what they called it. They were just "sick." It didn't take long for this "sickness" to spread. Everywhere.
No one could pinpoint where it started, but it was obvious how it spread- biting. If you were bitten by one of the infected, you would become sick and die within the week.
And then you would wake up again.
"Zombies, man! Real like zombies!" Dean laughed, hitting the steering wheel as he drove along the empty road, Sam beside him, as always.
"We don't know that for sure, yet," Sam didn't even look up from the newspapers he was reading as he talked to his overly-excited brother. It was about the most recent vic. A 30 year old nurse had been bitten by one of these "zombies" during his shift. He became increasingly sick, andafter 3 days of lying in bed, he died. The next morning, before anyone even knew he had passed, he woke up and attacked his wife.
At first they (or Dean at least) had almost been excited for this case. There were real, in-the-flesh, zombies! But soon it became apparent that this epidemic was nothing like they had ever seen before, and even the entire hunting community was powerless to stop it.
As it spread, it sent the world into panic. Chaos. Doctors and Hunters alike could not figure out how to stop it, or even how it started. The only thing they learned was how to kill them: by destroying the brain.
"So you're telling me that the only way to kill it is a head-shot?" Dean questioned his brother, who had just got off the phone with Bobby.
"I guess. Or you could bash its head in." Sam shrugged. "It's all about the brain. Apparently Rufus ran into some down in Florida. He shot it in the heart, used silver, salt, the works. Nothing killed it until he shot it right in the head."
In just a few months, the world was suddenly a scene from "28 Days Later." The government was gone, and most people were either dead or in hiding. The world was a totally different place... but the Winchesters had survived.
And they weren't the only ones.
