Inclusion criteria: Male and female subjects will be eligible for participation in this study if they: 1. Are ≥18 years on the day of screening 2. Have a chronic condition and have been treated with a B-cell depleting therapy (rituximab) within the last 12 months 3. Received mRNA SARS-CoV-2 (Biontech/Pfizer or Moderna) vaccine 4. Did not develop humoral immunity 4 weeks after second mRNA vaccination to SARS-CoV-2 (analyzed during the study “Characterization of immune responsiveness after mRNA SARS-CoV-2 Vaccination in patients with immunodeficiency or immunosuppressive therapy”, EK-Nr. 1073/2021, EudraCT Nr. 2021-000291-11) 5. A maximum of 6 months after second vaccination 6. Have an understanding of the study, agree to its provisions, and give written informed consent before study entry 7. If female and capable of bearing children – have a negative urine pregnancy test result at study entry and agree to employ adequate birth control measures for the duration of the study

Inclusion criteria: Male and female subjects will be eligible for participation in this study if they: 1. Are ≥18 years on the day of screening 2. Have a chronic condition and have been treated with a B-cell depleting therapy (rituximab) within the last 12 months 3. Received mRNA SARS-CoV-2 (Biontech/Pfizer or Moderna) vaccine 4. Did not develop humoral immunity 4 weeks after second mRNA vaccination to SARS-CoV-2 (analyzed during the study “Characterization of immune responsiveness after mRNA SARS-CoV-2 Vaccination in patients with immunodeficiency or immunosuppressive therapy”, EK-Nr. 1073/2021, EudraCT Nr. 2021-000291-11) 5. A maximum of 6 months after second vaccination 6. Have an understanding of the study, agree to its provisions, and give written informed consent before study entry 7. If female and capable of bearing children – have a negative urine pregnancy test result at study entry and agree to employ adequate birth control measures for the duration of the study

Inclusion criteria: Male and female subjects will be eligible for participation in this study if they: 1. Are ≥18 years on the day of screening 2. Have a rheumatic condition and have been treated with a B-cell depleting therapy (rituximab) within the last 12 months 3. Received mRNA SARS-CoV-2 (Biontech/Pfizer or Moderna) vaccine 4. Did not develop humoral immunity 4 weeks after second mRNA vaccination to SARS-CoV-2 (analyzed during the study “Characterization of immune responsiveness after mRNA SARS-CoV-2 Vaccination in patients with immunodeficiency or immunosuppressive therapy”, EK-Nr. 1073/2021, EudraCT Nr. 2021-000291-11) 5. A maximum of 6 months after second vaccination 6. Have an understanding of the study, agree to its provisions, and give written informed consent before study entry 7. If female and capable of bearing children – have a negative urine pregnancy test result at study entry and agree to employ adequate birth control measures for the duration of the study

Inclusion criteria: Male and female subjects will be eligible for participation in this study if they: 1. Are ≥18 years on the day of screening 2. Have a rheumatic condition and have been treated with a B-cell depleting therapy (rituximab) within the last 12 months 3. Received mRNA SARS-CoV-2 (Biontech/Pfizer or Moderna) vaccine 4. Did not develop humoral immunity 4 weeks after second mRNA vaccination to SARS-CoV-2 (analyzed during the study “Characterization of immune responsiveness after mRNA SARS-CoV-2 Vaccination in patients with immunodeficiency or immunosuppressive therapy”, EK-Nr. 1073/2021, EudraCT Nr. 2021-000291-11) 5. A maximum of 6 months after second vaccination 6. Have an understanding of the study, agree to its provisions, and give written informed consent before study entry 7. If female and capable of bearing children – have a negative urine pregnancy test result at study entry and agree to employ adequate birth control measures for the duration of the study