Declaration of competing interest The authors of this manuscript have conflicts of interest to disclose as described by the American Journal of Transplantation. M. Sester has received grant support from Astellas, Biotest, and Takeda to the organization Saarland University and honoraria for lectures from Biotest and Novartis and for advisory boards from Moderna, Biotest, MSD, and Takeda outside of the submitted work. B.C. Gärtner has received honoraria for lectures from BioNTech, Sanofi, CSL Seqirus, and GSK outside of the submitted work, and travel support for a conference from Pierre Fabre.