Guus F. Rimmelzwaan works at the intersection of human and veterinary medicine. He is an internationally eminent immunologist specialising in virus research, especially on influenza viruses that can occur in both humans and animals and potentially be transmitted from animals to humans and vice versa. He has worked intensively on bird flu as well as investigating, for example, the role of cats as possible vectors in the transmission of influenza viruses to humans. Rimmelzwaan has gained a special reputation for his research into t-cells in the immune system, demonstrating the importance of this group of white blood cells for more comprehensive protection against influenza viruses. One finding that has proven particularly relevant to both immunisation strategies and the development of new vaccines is that a vaccination against as many different influenza strains as possible is especially advantageous because the viruses can mutate so easily. As an Alexander von Humboldt Professor at the University of Veterinary Medicine Hannover, Foundation (TiHo), Guus F. Rimmelzwaan is invited to help put immunology and health research on a stronger international footing. At the same time, the Humboldt Professorship harmonises excellently with the one health strategy pursued at TiHo to consider human and animal health jointly at ecosystem level.