Peter Capaldi plays a doctor with the World Health Organization and is credited as "W.H.O. Doctor." The film makers had inside knowledge that Capaldi would soon be portraying the title role in Doctor Who (2005). The BBC publicly announced the casting two months after the film was released.
The original screenplay by J. Michael Straczynski was very different. The film was going to be a mockumentary told in a series of interviews and flashbacks about the zombie outbreak, ten years after it happened. The film was going to explore the psychological after-effects and societal changes that had occurred (cremation became the new norm, while burial became taboo). Director Marc Foster thought that Straczynski's story was too intellectual, though, and in a highly publicized move, got David Carnahan to rewrite it.
Before attempting to enter B-Wing, Lane and Segen are given the option of an ax or a baseball bat and are told "there are merits to each." This is an in-joke reference to a section of Max Brooks' "Zombie Survival Guide" (the book that preceded "World War Z") which discussed the best weapons to use when fighting zombies. The book considers both options superior to the gun, which Segen also takes as a backup.
J. Michael Straczynski's early draft of the script stayed closer to the source material. That version followed Gerry Lane, a UN worker tasked with investigating the failures that led to the outbreak so that they can be avoided in the future. The bulk of the narrative consisted of interviews with prominent figures and flashbacks to their role in the initial outbreak, largely taken from the book. This was framed by Gerry's journey around the globe to meet these individuals, showing the current condition of the human race, and flashbacks to the Lane family's struggle to survive in the wilderness in the early days of the war.
A total of 85 prop machine guns, rifles and pistols to be used for scenes filmed in Hungary, were confiscated by counter-terrorism customs officers in Budapest, Hungary after being flown in from London. Hungarian authorities said the guns could be activated by removing the screws filling the end of the barrels. Hungarian law requires weapons to be deactivated only if the process is irreversible. The movie's weapons supervisor, 'Bela Gajdos', commented that a permit for the weapons had been issued by Hungarian police. Reports claimed that main actor Brad Pitt was "furious" at the seizure but producers said it had not delayed filming.
In the beginning of the trailer released in March 2013, while Gerry's family is having breakfast the radio in the background mentions a flight which landed without permission before martial law is declared in Russia. This is likely the infamous Flight 575 alluded to in the book. Before Flight 575, a few people were able to smuggle infected loved ones out of China, where the authorities were rounding up the afflicted to control the disease. Some unspecified zombie disaster befalls Flight 575, leading to greatly increased scrutiny and restrictions. (In J. Michael Straczynski's script, the pilots lose contact with the cabin, but don't know that it's because the plane is overrun with zombies. They make an emergency landing in the US, and an unsuspecting SWAT team is overwhelmed as soon as they open the cabin door.)
In a high-six-figure deal, Paramount Pictures acquired screen rights to the Max Brooks novel "World War Z: An Oral History of the Zombie War." Brooks' follow-up to the satirical "The Zombie Survival Guide" sparked a bidding battle, with Warner Brothers & Leonardo DiCaprio's Appian Way on the other side of the table from Paramount & Brad Pitt's Plan B.
Paramount executive Marc Evans and Adam Goodman, the president of production did not like the original cut (which has the Russian ending) as both men felt that it was incoherent and abrupt. They brought in Damon Lindelof to view the cut and he suggested to them either to add new scenes to improve the coherence or do a complete third-act rewrite and risk additional resource plus re-shoots. Lindelof recalled: "So when I gave them those two roads and they sounded more interested in Road B I was like, 'To be honest with you, good luck selling that to Paramount."
A budget calculation oversight while filming in Malta partially contributed to the film being over budget. The wrap-up team found a stack of purchase orders for extras that was casually tossed aside in a drawer which was unaccounted for.
Filming took place in several areas of the UK including Cornwall, where the UN control room scene was filmed alongside scenes on the Ministry of Defence (MOD) Primary Casualty Receiving Facility (PCRF), RFA Argus (AS on the flight-deck). Filming also took place in Glasgow with the streets made to look like those in Philadelphia, USA with many American cars, trucks, taxis and street signage shipped in from the USA. Filming took place in Malta, at Valletta, and elsewhere.
The original cinematographer was Robert Richardson. He left the film near the end of principal photography to begin working on Django Unchained (2012), so shooting was completed by Newton Thomas Sigel. Reshoots were shot by Ben Seresin. Richardson, who received sole credit in early promotional material, later had his name removed from the film, reportedly because it was converted to 3-D against his wishes, and Seresin was given sole credit instead.
In the movie, Daniella Kertesz portrays a Lieutenant in the Israeli Defense Forces (IDF). In real life, Kertesz disclosed during an interview with "The Times of Israel" that she never served any compulsory time in the IDF, though she did not provide any details on this.
Director/executive producer Marc Forster states that he prefers the extended, unrated cut of the film. For him it's not just about the additional blood and gore, it's about the overall intensity compared to the PG-13-rated version. Forster says that although he's proud of the theatrical version, he felt a bit "handcuffed" when he was trying to deliver the toned-down PG-13-rated version.
The trivia items below may give away important plot points.
Originally, the film had a different ending: the plane lands in Moscow rather than crashing in Wales. The passengers are rounded up, and the elderly and sick are executed. Gerry is drafted into the Russian army. An unknown period of time passes, and we see Gerry fighting the zombies. He realizes the zombies are weak in the cold. The film ended with him getting back to the USA and leading a D-Day like invasion against the undead on the Oregon coast. The ending that was used instead made the movie less brutal and ended it with a glimpse of hope.
Matthew Fox had a bigger role in the film. He was a supporting character who in the end would be set up as a (human) villain for World War Z 2 (2017). Due to the constant re-writes and editing, his role in the final cut was reduced down to only 5 lines of dialogue.
The rewrite was almost at 60 pages long and cost an additional $20 million more. In addition to the new opening and the rewritten third act, the following snippets were added by Drew Goddard and Damon Lindelof, with Christopher McQuarrie doing uncredited dialog sharpening:
At the family breakfast, the TV news report of the zombie sighting.
Rachel's asthma attack
Gerry's phone call to Karen from South Korea to Jerusalem