Anti-Chalcedonian Christians like John of Tella, Severus of Antioch, Philoxenos of Mabbug, and John Rufus were concerned about orthodox Christians mingling with heretics. This essay argues that John of Tella combined narratives of heresy with those of bodily purity and pollution, such as those related to menstruation, to frame heretics as dangerous to orthodox Christians not only in their beliefs that could lure an unsuspecting Christian to accept heretical views, but in their very bodies whose proximity brought the threat of contamination. John integrated expectations of bodily purity and doctrinal orthodoxy in ways that suggested that heresy could physically contaminate, while Severus tried to calm his congregants’ fears about the same. The spread of COVID- 19 and the global responses to it have heightened our awareness of the dynamics of fear and anxiety that can be produced by threats of physical contamination. The global pandemic in 2020 thus helps to clarify the power that the rhetoric of these sixth-century anti-Chalcedonian texts had to confront the spread of what John of Tella implied was the dangerous physical pollution of Christian heresy.