Exclusion criteria: Subjects will be excluded from participation in this study if they: 1. Have shown humoral response to the SARS-CoV-2 vaccination 2. Had grade 3 adverse effects from the mRNA vaccination reported 3. Pregnancy and breast feeding 4. Signs of SARS-CoV-2 infection (including previous positive PCR testing) 5. Any other contraindication to any of the study compounds 6. Urgent need for next rituximab application

Exclusion criteria: Subjects will be excluded from participation in this study if they: 1. Have shown humoral response to the SARS-CoV-2 vaccination 2. Had grade 3 adverse effects from the mRNA vaccination reported 3. Pregnancy and breast feeding 4. Signs of SARS-CoV-2 infection (including previous positive PCR testing) 5. Any other contraindication to any of the study compounds 6. Urgent need for next rituximab application