Covid-19 affects some people much more severely than others. Some reasons for this such as old age are already known, but other as yet unknown factors also play a role. This summer, a large international study linked a group of genes on chromosome 3 to a higher risk of hospitalisation and respiratory failure upon infection with the Sars-CoV-2 virus. Researchers at the Karolinska Institutet in Sweden and the Max Planck Institute for Evolutionary Anthropology in Germany have now analysed the gene cluster.