This contribution investigates the structural causes behind the multiplication of medical and scientific expert opinions during the Covid– 19 pandemic in Italy. Drawing on Peirce’s concept of the interpretant and its connection with Eco’s notion of Encyclopaedia, the article examines two episodes, in which experts publicly supported contradictory positions regarding the effectiveness of both the Johnson & Johnson and the AstraZeneca vaccines. The episode is analysed through the lens of the theory of impersonal enunciation, focusing on the chaining of enunciative instances within the discourse of the experts, as well as on the encyclopaedic passages between scientific and media domains, which shaped the interpretive effects of the discussed interventions.