Danny Boyle has not discounted the possibility of a third installment. The working title is 28 Months Later, and would move the story on even further. But writer Alex Garland is a little more cynical: "I'll be honest. When we made 28 Days Later... (2002), the rights were frozen between people who no longer talk to one another. And so, the film will never happen unless those people start talking to each other once again. There is no script as far as I'm aware."

When Danny Boyle, Alex Garland and Andrew Macdonald first began to consider a sequel to 28 Days Later... (2002), their initial idea was to do 29 Days Later, possibly using the characters of Jim (Cillian Murphy), Selena (Naomie Harris) and Hannah (Megan Burns) from the first film. This idea was dropped in favor of doing a film set within the time-frame of 28 Days Later..., focusing on an SAS team sent into London to retrieve either the Prime Minister or the Queen. Finally, it was suggested to set the film some time after the events of the initial film, and to deal with the impact Rage has had on society in general.

It is stated on the DVD extras that all the actors who are playing infected people come from a "movement background": they have a history in dance, gymnastics, circus or mime. They also followed workshops to learn more about the infection and what they were supposed to do.

All of the night scenes involving Andy, Tammy, Scarlet, Doyle and Sam's journey across London to escape the bombs were shot day-for-night using a new technique created specifically for the film by director of photography Enrique Chediak. The scenes were shot day-for-night for three reasons. Firstly, because the filmmakers weren't allowed to use Mackintosh Muggleton (Andy) at night time. Secondly, because there is supposed to be a total shut down of all power in London, hence every building must appear light-less. However, if one were to actually shoot at night time in London, this would be impossible to capture photo-realistically and would hence involve complex post-production work removing all of the lights. By shooting during the day time however, there are few lights on in most buildings anyway, and as such, when the day-for-night treatment is applied to the film stock, everything in the image darkens equally, thus giving the impression that all of the buildings are in total darkness. Thirdly, director Juan Carlos Fresnadillo has always been a big fan of the 'ghostly' quality day-for-night shooting has, and he felt it would create the perfect sense of unease for the film.

Robert Carlyle had turned down the Christopher Eccleston part in 28 Days Later... (2002).

The boy who arrives at the cottage at the beginning of the film claims to be from Sandford. Sandford is the name of the 'fake' village that was used by British police to practice emergency preparedness drills. It's also the fictitious locale for the action comedy Hot Fuzz (2007).

Danny Boyle couldn't direct the sequel because of his commitments to Sunshine (2007). Cillian Murphy and Naomie Harris couldn't come back for the sequel either because of other commitments.

The farm that Don and Alice hide out in the start of the film is the same farm that appears in Children of Men (2006).

The Millennium Stadium in Cardiff doubled for the interior of Wembley Stadium because, at the time of filming, the interior of the newly built Wembley was still under construction. Visual effects were used to turn the seats red and make the grass appear untended.

According to director Juan Carlos Fresnadillo, composer John Murphy had only two weeks to compose the entire score for the movie.

The scenes where Andy is separated from Tammy, and subsequently escapes from District One with other survivors bears similarities with a flashback story from Mark (from 28 days later). Andy gets separated from Tammy just as Mark got separated from his sister. Andy escapes quarantine by climbing people and onto an air duct similar to how Mark climbed onto a kiosk. And Andy glimpses at the now infected Don stalking Andy from a distance similar to how Mark described watching his then newly infected father.

It was Alex Garland's idea to use the time line in the beginning of the film.

Most of the filming of the US Army Camp took place during the weekend of 21st/22nd October 2006 in the courtyard outside the Citypoint Building, Ropemaker Street, London EC2. A large number of tents with US flags, cast in military dress and vehicles were in place. Additionally access to the sub-floor car park area appears to have been given to shoot an underground scene.

The final film or TV role of Garfield Morgan.

The character of Doyle is a reference to the director of "28 Days Later," Danny Boyle. The name "Doyle" consists of the d from "Danny," and the "oyle" from Boyle, making Doyle.

Several actors in this movie would eventually appear in Marvel Comics-based Movies. Rose Byrne (Chief Medical Officer Major Scarlett) played CIA operative Moira Mactaggert in X-Men: First Class (2011) and X-Men: Apocalypse (2016) while Jeremy Renner (Delta Sniper Sgt. Doyle) played Hawkeye in Thor (2011), Avengers (2012), Avengers: Age of Ultron (2015), and Captain America: Civil War (2016). Idris Elba (General Stone) played Heimdall in Thor (2011), Thor: Dark World (2014), and Thor: Ragnarok (2017) while Amanda Walker (Sally) played the Antique Shop Owner in Captain America: The First Avenger (2011).

The iconic last shot was a last minute addition to the movie. The shooting script ends with the shot of the parked helicopter, and this was supposed to be how the film ended. However, two days before the locked off edit was supposed to be handed in to Fox Searchlight for distribution, writer/director Juan Carlos Fresnadillo, writer/producer Enrique López Lavigne and co-producer Bernard Bellew flew to Paris to shoot the scene with which the film now ends. This scene was conceived at the last minute by Fresnadillo and López Lavigne, and was shot completely guerrilla style, with only the three crewmen, twelve local actors hired on the day of the shoot, and one DV camera. Sound for the scene was rapidly mixed back in London, and the shot was hastily added to the end of the film.

In the shooting script, it is Scarlet (Rose Byrne) who is burnt to death whilst trying to get the car started and Doyle (Jeremy Renner) who is beaten to death by Don (Robert Carlyle) in the subway. Writer/director Juan Carlos Fresnadillo and writer/producer Enrique López Lavigne changed this at the last minute because they felt that killing Doyle first and leaving the children with Scarlet would create more tension for the audience, as leaving the children with Scarlet as opposed to Doyle makes them seem more vulnerable.

Danny Boyle directed some of the second unit filming, and also directed one first unit sequence; the scene in the barn near the start of the film where Sally (Amanda Walker) and Geoff (Garfield Morgan) are killed.

(Also spoiler for 28 Days Later... (2002)): Series Trademark - Eye Gouge killing: When Don attacks his wife after becoming infected, he attacks her and presses her eyes in with his thumbs. In the film's predecessor 28 Days Later... (2002) Jim attacks and kills a guard in the mansion using the exact same technique.