During the COVID-19 pandemic, the clinical spectrum observed among people infected with SARS-CoV-2 ranged from asymptomatic carriage to death. Researchers at the Institut Pasteur, the CNRS and the Collège de France, in collaboration with researchers around the world , have investigated the extent and drivers of differences in immune responses to SARS-CoV-2 across populations from Central Africa, Western Europe and East Asia. They show that latent cytomegalovirus infection and human genetic factors, driven by natural selection, contribute to population differences in immune response to SARS-CoV-2 and the severity of COVID-19. Understanding the factors underlying such population disparities could help to improve patient management in future epidemics. These results were published on August 9, 2023 in Nature.