Hey there, I've been writing an essay I need to turn in for one of my general eds and I needed to set it up so that every human is wiped out except some strange, tinfoil-hat family somewhere in some underground bunker and I decided to use some biological weapon in my story. Unfortunately, I don't have much knowledge in biology and I'd like to know how plausible, or if it's even possible, this would be: A man-made virus that's very infectious (it'd infect people the same way the common cold spreads), has a 100% mortality rate (I don't know if this is possible), and stays in incubation for a long period of time. The idea is that some crazy guy spreads it in some place, and it starts rapidly spreading - but since it doesn't display any symptoms for quite a while, let's say a year or two, it remains unnoticed until it becomes active, at which point every human is infected. Is this even remotely possible? I doubt my professor would care about the details, but if it's obviously impossible because of some reason, I'd like to consider some other method for my story.