The United States government lied - again.
They convinced desperate citizens, looking to escape the next monstrous wave of the never ending epidemic into signing up as part of a nation wide experiment that, if successful, would make their immune systems invincible to further viruses.
Of the half a million Americans believed to have taken the vaccine, only thousands survived.
But of those that have survived they were, in fact, reborn.
With a thirst for vengeance and blood.