Letters from Balmis to Gutiérrez: fracture of the friendship between two vaccine expeditionary personages.

The Royal Philanthropic Vaccine Expedition (1803-1813) becomes relevant in these pandemic times due to the breadth of its geographical dimension and its nature of a health expedition inspired by a pioneering public health objective of its time: to spread the newly discovered vaccine against smallpox. Undertaken by a small number of participants, the expedition was directed by Francisco Xavier Balmis, who was accompanied, among others, by Antonio Gutiérrez Robredo, his favorite disciple. This research, carried out using primary sources, explores the relationship between both, which went from mutual trust to enmity due to a trivial conflict. The study of previous correspondence and late resolution of the lawsuit filed by Balmis against Gutiérrez allows us to delve into their biographical profiles. As a direct consequence of that litigation, Gutiérrez never went back to Spain, although he became a professor in Mexico; in contrast, Balmis enjoyed honors and recognition in Madrid.