That's the problem with this movie. This movie looks like it will have nothing to do with the book. Why bother calling it World War Z if they doing follow the book at all except for the token gesture of giving one of the character the same?
Copy right laws.
It's close enough to the book that Paramount would get their asses sued if they didn't acknowledge the writer by naming the film after his book and paying him a shit load of money for the rights.
Trust me if they could have retitled the film, "Zombie Wars" - not paid the writer of the book a nickel and still gotten Brad Pitt to star in the film they would have in a heartbeat.