This chapter conceptualizes vaccine pharmacovigilance as the institutional site where the ambivalence of vaccines—as pharmakon, both remedy and potential harm—is continuously negotiated. Drawing on feminist STS and broader scholarship on knowledge production and infrastructures, it argues that vaccine “safety” is not simply detected but made through classificatory and regulatory practices that transform embodied experiences into evidence. Building on Jain’s notion of the ‘WetNet’ and Lesmo’s reworking of it for pharmacovigilance, I describe vaccinovigilance as a circulation system characterized by two coupled movements: liquefaction, as reports travel upward and lose social and affective texture to become analyzable signals, and sedimentation, as global standards move downward and harden into local practice, often excluding what they cannot capture. Two empirical cases—the 2014 HPV controversy in El Carmen de Bolívar (Colombia) and menstrual disturbances reported after COVID-19 vaccination in Europe—show how epistemic hierarchies and intersectional marginalities shape what becomes visible, credible, and actionable. The chapter concludes by proposing more inclusive forms of vigilance that do not eliminate uncertainty but cultivate the capacity to attend to it as a condition of care, accountability, and trust.