Nearly one in three people exposed to SARS-CoV2 is infected, and as many as two in five with the Omicron variant. In the case of immunity — conferred by vaccination, infection or a combination of the two — this rate drops to one in ten. However, immunity disappears within a few months, confirms a team of researchers, after revisiting epidemiological data collected in Geneva. While protection following infection appears to be slightly greater than after vaccination — albeit at the risk of potentially severe symptoms — vaccination reduces the contagiousness of patients over a longer period. As the number of cases rises again, air filtration, ventilation and the wearing of masks in the vicinity of vulnerable people appear to be necessary measures.