So this appears to bear no relation whatsoever to the book aside from having zombies in it and the same title. Why would they bother calling it this?
As a movie, WWZ shouldn't have a big star who's the protagonist. It's a series of vignettes describing different human responses to what appears to be the end of human civilization. Eventually, a strategy is developed that slowly but surely pushes back the tide and after years of work the Zack problem is gradually eliminated. There's no big climactic moment where they figure out how to defeat the zombies and Brad Pitt does somethign heroic and epic music plays in the background and humanity survives, and you just know that's what's going to have to happen here.
This is whack!