Since the dawn of the beginning of the start of time itself, zombies have been provided important symbols for our novels, movies, and video games.
All right, maybe we overshot a little bit.
But, we can safely say, without exaggeration, that every good zombie story has the zombies amount to more than flesh-devouring horrors sent from beyond the grave to plague humankind. Those undead buggers provide an important symbolic core to the tale, and World War Z is no exception.
What do the zombies represent in the novel? There's no simple answer, but if we had to sum it up succinctly, then we'd probably say they symbolize disaster at its most extreme.
Take a minute and really check out the language and imagery employed to describe the zombies. You'll notice a lot of different comparisons at work:
The point is that they exhibit all of these qualities together, meaning that they symbolically reference all these things at the same time. The zombies are war, natural disasters, plague, destruction, and—not least—human evil all embodied in an undead body. Or as Max Brooks put it:
The lack of rational thought has always scared me when it came to zombies, the idea that there is no middle ground, no room for negotiation. That has always terrified me. Of course that applies to terrorists, but it can also apply to a hurricane, or flu pandemic, or the potential earthquake that I grew up with living in L.A. Any kind of mindless extremism scares me, and we're living in some [pretty] extreme times. (Source.)
So, the zombies are all these things and also the fear of all these things rolled into one. When the characters of World War Z battle against the groaning ghoulies, they also battle symbolically against these extreme aspects of our existence as well.
While the ghoulies often signify really big disasters in the novel, they can also symbolize smaller disasters or challenges.
We have an example for you. Colonel Christina Eliopolis is a woman pilot in the man -centered society of the U.S military. In one scene she mentions, "My crew, the 'guys,' used to give me a lot of grief, you know, girls always having to go. I know they weren't really putting the hate on, but I still tried to hold it as long as I could" (6.5.25). It's a small thing, but her reaction to the joke shows how seriously she takes the matter personally.
After her plane crashes, she has to survive in the wilderness, against the zombies, alone. Here, the zombies still exist as a symbol of horror, but the horror becomes more personal challenge than global calamity. Eliopolis must overcome her own fears and insecurities as a woman, and the zombies are the obstacles in her path.
So, just to sum things up: zombies represent everything bad that we have to overcome—individually, nationally, and globally. How's that for a symbol?