The degree to which a virus spreads depends on its infectivity. While the coronavirus SARS-CoV-2 has led to severe pandemic, a related virus, SARS-CoV, led to a much smaller outbreak in 2003, possibly because the infection was limited to the lower respiratory system. SARS-CoV-2, in contrast, infects the upper portions of the respiratory tract, including the nasal mucous membrane and, in consequence, spreads rapidly through active viral shedding. Researchers at TUM, the German Center for Neurodegenerative Diseases (DZNE), the University Clinic Universitätsmedizin Göttingen and the University of Helsinki have investigated the nature of SARS-CoV-2 infectivity.