The Revaccination Conundrum: Debates on Contagion and Immunity in Pre-Unitarian Italy

Despite the introduction of vaccination during the Napoleonic era (1800–1814), several smallpox epidemics broke out on the Italian peninsula in the first half of the nineteenth century. From 1815 onwards, Italian physicians began questioning the medical knowledge that Edward Jenner and Luigi Sacco had codified and rethinking the nature of smallpox contagion: in particular, they asked themselves whether the vaccinal immunity was to be considered universal and permanent, and whether the vaccinal lymph could lose its immunizing power due to excessive interhuman transmission and a consequent degeneration. By examining the evolution of such a scientific debate through an analysis of the involvement of famous medical practitioners and the institutions in which it took place (e.g., universities, academies, scientific congresses, etc.), this paper sheds light on the emergence of the concept of temporary immunity and the acknowledgment of the need for revaccination. Moreover, it highlights the fact that the lack of decisive medical-epidemiological evidence, which could have proven and explained the temporariness of the vaccinal protection, prompted physicians to elaborate various methods for achieving consensus on their theses, which audaciously combined medical, statistical, political, and rhetorical issues. Finally, it shows that the internal division of the Italian medical community between supporters and opponents of revaccination frequently depended on their regional origin and their role in pre-unitarian State health institutions, thus demonstrating the crucial entanglement between politics (i.e., the efficiency of each State’s vaccination policies, the resources invested in public health initiatives, etc.) and science in the development of medical knowledge.