I am half way through "World War Z" and I can see why fans of the book were so upset about the movie. The book and the movie are thematically two different stories. The book is a series of different people's accounts of the worldwide zombie outbreak and war, as told to the interviewer/narrator. The movie (which I enjoyed despite my fear of zombies), is an action/adventure zombie movie, which features fast running zombies, armed forces fighting zombie hordes, a worldwide search for a cure, a plane crash, and a tense final scene set in a World Health Organization infectious diseases research laboratory.
I don't understand what Brad Pitt and his production company Plan B were thinking when they wrote, shot, and produced the 2013 movie, under the title "World War Z." The book's plot reminds me a more of Steven Soderbergh's 2011 multi-narrative "medical outbreak" movie "Contagion", which featured an all-star ensemble cast of Laurence Fishburne, Jude Law, Marion Cotillard, Gwyneth Paltrow, Kate Winslet, and Matt Damon, than the single-narrative "28 Days Later"-type ravenous infected/zombie movie that Pitt and co. created.