The screenplay is credited to M. Sussman and John Kingswell (neither has any other film credit of any kind). Several writers, including David Ayer and Paul Mones were rumored to be working on the script prior to its release; Mones was ultimately credited as a producer. Though the movie is credited as an adaptation of William C. Heine's novel "The Last Canadian", it shares virtually no similarities with the novel except the idea of a deadly virus. No character names, events, or even locations appear in both the book and the film.