Zombie Apocalypse

After an explosion in a research lab, the first responders were exposed to a prototype neurotoxin called A526. At first there were just skin irritations and a fever, then the skin began to pale and eventually turned grey. Then they collapsed unconscious. Minutes later they woke back up and began to infect the uninfected. Months after the incident the army fell, then the country, then the world. Obviously some people did survive, settlements etc. It's your story from now on.