The sequel movies, 28 Years Later, didn’t exactly set the world on fire. They were created and launched to a fnafare, and critics were positive, but audiences seemed less sure. By the time 28 Years Later: The Bone Temple had completed its cinematic run, it was clear that coming so soon after the first 28 Years Later, with its mixed reception, meant that even the critical buzz the movie recieved couldn’t translate to box office.
So it has been assumed that, given a near $20 million loss across both movies, the studio would not be proceeding with the planned third movie. The studio had made positive noises during the build up to opening, but since then, the studio has gone very quiet, with many assuming that silence meant that they were no longer proceeding.

Until actor Alfie Williams, who played Spike in the first two sequel movies, made an Instagram post where he appeared to be practicing archery, ready for filming, with the caption:
“It’s Great to be Back”.
The post was immediately seized upon online as proof that production on the third movie is gearing up.
Danny Boyle and Alex Garland have already written the third movie, and secured Cillian Murphy to return in a more major capacity for the finale. Sony may be gambling that his return, and the closure of the franchise, could generate enough buzz to make it worthwhile.