The film differs from the novel (and the previous film) in several ways. In the novel, humanity is destroyed by a bacterial plague spread by bats and mosquitoes, which turns the population into vampire-like creatures, whereas in this film version, biological warfare is the cause of the plague that kills most of the population and turns most of the rest into nocturnal albino mutants. Screenwriter Joyce Corrington holds a doctorate in chemistry and felt that this was more suitable for an adaptation.