As originally announced in March 2007, Danny Boyle has had thoughts and plans for a third film in the 28 Days Later series, which will be given the title 28 Months Later. Boyle stated that he had thought to set the movie in Russia. In June 2007, it was announced that if DVD sales of 28 Weeks Later did well, Fox Atomic would consider producing the third film.

In July 2007, while promoting Sunshine, Boyle revealed that he has a story formulating for the next film. "There is an idea for the next one, something which would move [the story] on. I've got to think about it, whether it's right or not." Boyle also revealed that he would return as the director. Alex Garland (the screenwriter of the first film), on the other hand, said in October 2010: "When we made 28 Days Later, the rights were frozen between a group of people who are no longer talking to each other. And so, the film is never going to happen unless those people start talking to each other again. There is no script as far as I'm aware."

However, Boyle stated on April 13, 2013: "It's 40/60 whether [a sequel] happens or not. But we did have an idea of where to set it and what it might be about;" and Alex Garland likewise said in January 2015: "We've just started talking about it seriously. We've got an idea. Danny and Andrew and I have been having quite serious conversations about it so it is a possibility. It's complicated. There's a whole bunch of reasons why it's complicated, which are boring so I won't go into, but there's a possibility."

In January 2019, Boyle confirmed that he had recently met with Garland to begin pre-production on 28 Months Later.

In January 2024, it was announced that a third film titled 28 Years Later, was officially in development; with plans for the project to be the first of a new trilogy of sequels. Danny Boyle will direct the first installation, with a script written by Alex Garland; while the latter will write the scripts each of the planned movies in the three releases. Boyle, Garland, Andrew Macdonald, and Peter Rice will serve as producers. Andrew Macdonald, and Peter Rice will serve as producers. In February of the same year, Murphy discussed his potential involvement with the project. In March 2024, Garland confirmed that he is writing a trilogy of sequel films. The following month, the writer stated that Kes was a major influence on his work for 28 Years Later.