In every zombie movie the biggest threat to your survival is going to be your fellow survivors. Why?
Because survivors are dumb, and writers can be very very lazy. (I know I am)
Did you see the remake of “Dawn of the Dead” Good, crap! “Well, we’re all safe and secure, with plenty of food in this big mall. Sure we could wait this whole thing out and survive… oooooooorrrr we could string a succession of poor decisions together and other improbably crap until we are all dead! Sound like a plan?”
By the end of that movie I was praying they would all die. And not just because I’m a horrible person.
My point is that survivors are dumb.