The securitization of health concerns within the European Union has hitherto received scant attention compared to other sectors. Drawing on the conceptual toolbox of actor-network theory, this article examines how a 'health security assemblage' rooted in EU governance has emerged, expanded, and stabilized. At the heart of this assemblage lies a particular knowledge regime, known as epidemic intelligence (EI): a vigilance-oriented approach of early detection and containment drawing on web-scanning tools and other informal sources. Despite its differences compared to entrenched traditions in public health, EI has, in only a decade's time, gained central importance at the EU level. EI is simultaneously constituted by, and performative of, a particular understanding of health security problems. By 'following the actor', this article seeks to account for how EI has made the hunt for potential health threats so central that detection and containment, rather than prevention, have become the preferred policy options. This article draws out some of the implications of this shift.