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 Weeks Later..., focusing on a 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.
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."
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.
The boy who arrives at the cottage at the beginning of the film claims to be from Sandford. 'Sandford' is the name of a 'fake' village used by the British police to train recruits and practice emergency preparedness drills, the street plan of which is based on that of Dundee, Scotland. Sandford is also the fictitious locale for the action comedy Hot Fuzz (2007). This may be an in-joke to the fact that the team behind Hot Fuzz had previously made Shaun of the Dead (2004), a zombie comedy that poked fun at 28 Days Later (2002) by dismissing "rage infected monkeys" as the source of its own zombie plague. By mentioning Sandford, the makers of 28 Days/Weeks Later now seem to be returning the favor.
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).