The film was shot almost entirely in sequence; only pickups and a few reshoots were shot out of sequence.
The scene where Jim and Selena celebrate with Frank and Hannah was shot on September 11, 2001. Danny Boyle said it felt extremely strange to shoot a celebratory scene on that particular day.
For the scenes on the motorway, the production got permission to shoot on the M1 on a Sunday morning between 7.00am and 9.00am. The police gradually slowed traffic in both directions. Using 10 cameras, the filmmakers managed to capture a total of one minute of usable footage.
Athletes were cast as the Infected because of how important physicality is to them. Danny Boyle felt that since athletes can do things other people can't, they would be interesting when translated into the movements of the Infected.
Alex Garland and Danny Boyle did a great deal of research into social unrest, drawing ideas from things that had happened in Rwanda and Sierra Leone (such as the piling of bodies inside churches), but drew the line at using any actual footage from such incidents in the opening montage. All footage featuring dead bodies/desecration of bodies was faked.
The hospital in the film is a real day hospital, open only during the week. The trust managers of the hospital hire out the building to filmmakers for weekends, and the productions pay the hospital directly, meaning the money from filming goes directly to the hospital's trust fund.
Ewan McGregor was the original choice to play Jim, but he and director Danny Boyle had a falling-out at the time over The Beach (2000), in which McGregor was supposed to play the lead until he was replaced by Leonardo DiCaprio (they have since reconciled). After that didn't work out, the role was offered to Ryan Gosling, who had a scheduling conflict.
Horror novelist Stephen King bought out an entire showing of the film in New York City.
The crew filed all of the necessary papers to destroy the Canary Wharf petrol station, but the police were (unintentionally) not notified. When the explosives were detonated, police sent fire brigades (although one was already present). Danny Boyle resolved the matter after several hours. The explosion cost £250,000 total.
One of the first mainstream films to be shot entirely digitally as opposed to with film.
For the London scenes, police would close the roads at 4am, and filming would begin immediately. After 1 hour, the police would reopen the roads. The producers correctly predicted that asking drivers (including clubbers headed home) to either wait for up to an hour or find another route might make some of them angry. They got several extremely attractive young women (including Danny Boyle's daughter) to make the necessary requests, and the drivers responded quite amicably to them.
The news footage which begins the film was based on footage shot by the journalist Sorious Samura in Sierra Leone.
Alex Garland and Danny Boyle felt that the notion of the living dead wanting to eat peoples' brains was outdated. One of the original factors behind zombie movies was a fear of nuclear power and its possible effects on people. Garland and Boyle concluded that one of the biggest fears in modern society is fear of disease, especially a viral apocalypse, such as Ebola or Marburg. Garland and Boyle were specifically inspired by such incidents as anthrax and bio-terrorism scares in London and the spread of mad cow disease and foot-and-mouth disease in the UK.
The 'design' for the symptoms of Rage was based on Ebola, which is communicable in all primates (including humans), and is transmitted through the blood. Ebola is a hemorrhagic fever which leads to a rash, red eyes and both internal and external bleeding. Indeed, in 28 Days Later: The Aftermath (a graphic novel set between 28 Days Later and 28 Weeks Later (2007), it is explained that the Ebola virus was being used by the scientists as a carrier for the inhibitor which mutated into Rage.
The scene when Jim finds the money on the steps and picks it up, was based on a photograph Danny Boyle had seen of Cambodia after Pol Pot had been driven out.
The extras who played the dead bodies in the church were college students who volunteered to appear in the film.
The shot where Jim sees the dead mother holding onto her dead baby is based on a photograph Danny Boyle saw of a mass of Kurd bodies after they had been gassed.
The shot of the notice board at Piccadilly Circus, with the missing persons fliers, caused some controversy when the film was first released. Some said it was insensitive to what happened in New York after the 9/11 attacks. The film was shot prior to 9/11/01, although it was released afterward. Danny Boyle said he based the shot on a photograph he saw from an earthquake in China. He also said that if he'd made the movie after the 9/11 attacks, he wouldn't have shot that scene.
All of the mansion scenes that involved upstairs rooms were filmed downstairs because the mansion's owner lives upstairs. When Jim jumps through the window in the roof, he is actually jumping through a hole in the corridor upstairs down to the ground floor.
The tower block where Hannah and her father lived is Belfron Tower which has been converted into luxury flats
The symbol used for this film is the international symbol for blood-borne biohazard.
The decision to film on DV (using Canon XL1 cameras) was both an aesthetic and a logistic choice. Aesthetically, Danny Boyle felt that the harshness of the DV imagery suited the post-apocalyptic urban landscape and the grittiness of the film in general. In the production notes, Boyle says "the general idea was to try and shoot as though we were survivors too." Logistically, producer Andrew Macdonald claims that shooting with standard cameras, especially some exterior scenes, would've been impossible. As MacDonald points out in the production notes, "The police and the local authorities were quite happy to assist us because we could set up scenes so quickly. We could literally be ready to shoot with a six-camera set-up within minutes - something we would not realistically have been able to do if shooting under the restrictions of 35mm which takes a good deal more time to set up a single shot."
The scene where Jim, Selena and Mark shelter from the explosion by hiding between the windows was based upon a photo Danny Boyle had seen of a bomb blast in Northern Ireland.
Stephen King is a huge fan of the movie and paraphrases one of Selena's lines in his novel, "Doctor Sleep", "He needs us more than we need him".
The tunnel scene was filmed in a new tunnel extension which the filmmakers had special permission to use.
The film includes heavy product placement for Britain's National Lottery, which funds the British Film Council.
The Bible verse on Jim's postcard is from the Book of Nahum. Nahum was a prophet who predicted the destruction of the great city of Nineveh, the capital of the Assyrian empire. It was to be utterly destroyed as a punishment for its inhabitants' sins.
Included among the "1,001 Movies You Must See Before You Die" edited by Steven Schneider.
Although unconfirmed, the title may refer to the fact that peak immunity from a virus is widely considered to occur 28 days after an infection is contracted.
Cillian Murphy was suggested to Danny Boyle for the role of Jim by Paloma Baeza, who had acted opposite him in Sunburn (1999) and The Way We Live Now (2001), playing his love interest in both productions. She would appear as his sister in Danny Boyle's Sunshine (2007).
Danny Boyle intentionally sought out unknown and obscure actors for the majority of the leading roles, as he wanted the film to be discovered and not rely solely on star power. Cillian Murphy, Naomie Harris, Noah Huntley, and Megan Burns were virtually unknown prior to the film production, with Murphy and Huntley having only had minor roles in films, Harris only having done British television, and Burns having only had one previous acting credit. The only famous actors of note that were cast were Brendan Gleason and Christopher Eccleston.
Jim, Selena, Mark, Frank, and Hannah's surnames are never revealed during the film or in the end credits. Likewise, Jim's parents names are never revealed.
The angelic song that plays in the background, particularly during the car trip, is Gabriel Fauré's "In Paradisum".
The single malt whisky that Frank is discussing with Jim in the supermarket is from the Lagavulin distillery. The whisky is part of the Classic Malts series and is known to be one of the smokiest and peatiest scotch whisky around. Frank appears to be a connoisseur considering his comments on the whisky when he says "peaty aftertaste" and "takes out the fire but leaves in the warmth".
If you actually traveled 27 miles northeast of Manchester, you would end up in Huddersfield, West Yorkshire.
The film's famous climactic score 'In the House - In a Heartbeat' by John Murphy was used in the sequel 28 Weeks Later (2007) and later in various films and trailers, for example for the films, I Know Who Killed Me (2007), Kick-Ass (2010) (for which Murphy also wrote the score), the trailer of the video game Metro 2033 (2010) and a Louis Vuitton commercial in 2012.
A scene that was shot and later abandoned involved a taxicab full of people singing The White Stripes' "Hotel Yorba".
Megan Burns retired from acting after appearing in this film, not wishing to pursue a full-time career as an actress, and instead focused on her passion for music and singing. She would not do another film for 16 years until she was cast in In2ruders (2018)
Megan Burns only had one previous film credit prior to this film, in Liam (2001) as Teresa. Danny Boyle selected her for the role of Hannah based on the strength of her performance in that film. She was his first and only choice.
Cillian Murphy would go on to star in the sci-fi thriller, Sunshine (2007), along side Rose Byrne who had starred in 28 Weeks Later (2007), the sequel to this movie.