Living in social groups leads to a high risk of disease spread. Insect societies counteracted this threat by evolving sophisticated collective anti-parasite defences, combining the immune systems of all group members and their collective social hygienic behaviours. I recently described a direct link between these social and individual defences, by showing that social contact to an infected individual results in a protective Social Vaccination in its nestmate ants: the latter survived an infection with the same pathogen significantly better than control ants that had lived with other healthy ants only. Aim of this project is to elucidate the molecular and physiological mechanisms of this Social Vaccination in individual ants, and its effect on the organisation of collective defences and disease dynamics at the colony level. Preliminary results have shown different protein upregulation in healthy, infected and vaccinated ants, and a detailed analysis of gene and protein expression patterns will define those proteins and their function in anti-parasite defence (postdoc). Observations of the social interactions between infected ants and their group members, and measures of the physiological immune responses of the individuals at different stages of the infection and after the vaccination will further reveal when and how Social Vaccination occurs, how long it endures, and how specific and plastic it is (PhD 1). At the colony level, the social role of vaccinated individuals and the fate of infected ants when loosing their vaccination potential will be determined, as well as the effects of Social Vaccination on disease spread in the colony and the regulation of collective defences between group members (PhD 2). This unique combination studying both the social and individual aspect of immune defences makes this project valuable for the fields of Social Evolution and Ecological Immunology, and further impacts on Epidemiology, Evolutionary Medicine and Biocontrol.