The lethal virus in "Doomsday" differs from contemporary films like "28 Days Later" and "28 Weeks Later" by being an authentic plague that actually devastates the population, instead of infecting people so they become aggressive cannibals or zombies. Marshall intended the virus as the backdrop to the story, having survivors scavenge for themselves and set up a primitive society. The director drew from tribal history around the world to design the society. Though the survivors are depicted as brutal, Marshall sought to have "shades of gray" by characterising some people in England as selfishly manipulative.