[The vaccine metaphor. From inoculation to vaccination].

The episodes of cowpox inoculation (1798) and rabies preventive treatment (1885) are celebrated as the landmark of modern medicine. Paradoxically, these two advances have been accomplished without any theoretical breakthrough in the understanding of immunity. Going further, they were made possible by a long past of empirical procedures among which smallpox inoculation played an outstanding role. The paper explores the paradox of 'Immunization without Immunology' and Pasteur's reconstruction of the past, through his successful use of a metaphor. 'Vaccine', originally linked to the jennerian method, was meant by Pasteur to designate a general program of virus attenuation. The paper investigates the scientific factors accounting for why viruses played such a leading role in immunization. The longlasting immunity, the easy transmission from man to man characteristic of smallpox allowing in vivo experimentation, may explain how crude procedures of early immunizers shaped scientific ideologies and strategies of public health and family initiated modern 'vaccinology'.