Apparently because of poor box-office results, this film was the last to be released by Film Ventures International (FVI). Edward L. Montoro, president of FVI, disappeared shortly afterward, taking $1,000,000 from the company's coffers with him. Nothing has been heard from him since.
Writer John C. Kruize stated in an interview that the monsters were never "intended to be pasty-faced, shambling zombies."
A sequel was written in the early 2000s but was never filmed. Bo Hopkins was attached to the project and was set to reprise his role as Sheriff Will Stewart. A part was also specially written for Ken Foree.
President of Film Ventures International Edward L. Montoro was responsible for most of the changes in the script after the rewrite process. Writer John C. Kruize admits some of the changes were good or acceptable (changing the germ warfare premises to toxic waste poisoning) but most weren't. During this process the title was changed to "Night Shadows", which the writers thought was weak.
According to writer John C. Kruize the title was changed to "Mutant" prior to release in an attempt to mimic the success of Alien (1979).