In Annie Vivanti’s Naja Tripudians (1920), London has been struck by a moral contamination that, spreading out from the center, has reached the sleepy rural village of Wild-Forest, where it will infect and eventually consume Leslie and Myosotis Harding. Though their father is a contagious disease specialist, he proves entirely incapable of protecting them from this contagion—and not only because it is home-grown. Perhaps more significantly his failure has to do his reliance on strategies of isolation and confinement, which not only prove ineffective in shielding his daughters from danger but also render them paradoxically more susceptible to the contagion. Although the novel was written during the Influenza Pandemic of 1918, critics have given little attention to the figures of immunity and contagion that structure the novel. By attending to these discourses, I argue that this novel can be read as anticipating in important respects Esposito's reflections on immunity. Though many have seen Naja Tripudians as a morality tale, I argue that the novel is better understood as a kind of 'anti-morality' tale, warning against the immoral things that result from resisting immoral things. The immunitary logic of the novel seems to suggest, in the end, that the preservation of moral virtue requires that we expose ourselves to the source of contamination, perhaps that we even behave a little badly ourselves.