After nine years, a potential The Maze Runner 4 can answer a long-running franchise mystery that I, and millions of other fans, have been desperately waiting for an answer to. The second installment of James Dashner’s book-to-movie The Maze Runner series, The Scorch Trials (2015), introduces the Flare virus, a man-made, brain-eating disease created by the Post-Flare Coalition (PFC) for population control – which evidently backfired. However, the film leaves other details about the Flare up to interpretation, creating several unresolved plot points.

https://screenrant.com/maze-runner-4-answer-question-flare-virus-origin/