The genetic variants we are born with can increase or decrease our risk of falling seriously ill with Covid-19. The major genetic risk variant for severe Covid-19, one we inherited from Neandertals, is surprisingly common. This raises the question whether it may actually be of advantage to carry this variant. A study by Hugo Zeberg, a researcher at the Max Planck Institute for Evolutionary Anthropology (MPI-EVA) in Leipzig, Germany, and Karolinska Institutet in Sweden, now shows that the same gene variant that increases the risk of falling seriously ill with Covid-19 protects from another serious disease – it reduces a person’s risk of contracting HIV by 27 percent.