a) Male and female patients will be eligible for participation in this study if they: 1. Are ≥18 years on the day of screening 2. Being immunocompromised (either primary or secondary immunodeficiency or been treated with immunosuppressive therapy within the last 12 months Immunosuppressive therapies include glucocorticoids, cytostatics, antibodies, drugs acting on immunophilins and other treatments like interferons and TNF binding proteins and exclude patients under B cell depleting therapy (like Rituximab, Ocrelicumab, Ofatumumab, Epratuzumab or Obinutuzumab) 3. Received two doses of SARS-CoV-2 (Biontech/Pfizer, Moderna) vaccine according to recommendations in the label and/or national guidelines. 4. Did develop < 1500 U/ml of SARS-CoV-2 antibodies 4 weeks after second mRNA vaccination (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, or external routine evaluation of humoral response) 5. A maximum of 12 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 b) Male and female healthy controls will be eligible for participation in this study if they: 1. Are ≥18 years on the day of screening 2. Received two doses of SARS-CoV-2 (Biontech/Pfizer, Moderna) vaccine according to recommendations in the label and/or national guidelines. 3. Did develop < 1500 U/ml of SARS-CoV-2 antibodies 4 weeks after second mRNA vaccination 4. A maximum of 12 months after second vaccination 5. Have an understanding of the study, agree to its provisions, and give written informed consent before study entry 6. 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

a) Male and female patients will be eligible for participation in this study if they: 1. Are ≥18 years on the day of screening 2. Being immunocompromised (either primary or secondary immunodeficiency or been treated with immunosuppressive therapy within the last 12 months Immunosuppressive therapies include glucocorticoids, cytostatics, antibodies, drugs acting on immunophilins and other treatments like interferons and TNF binding proteins and exclude patients under B cell depleting therapy (like Rituximab, Ocrelicumab, Ofatumumab, Epratuzumab or Obinutuzumab) 3. Received two doses of SARS-CoV-2 (Biontech/Pfizer, Moderna) vaccine according to recommendations in the label and/or national guidelines. 4. Did develop < 1500 U/ml of SARS-CoV-2 antibodies 4 weeks after second mRNA vaccination (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, or external routine evaluation of humoral response) 5. A maximum of 12 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 b) Male and female healthy controls will be eligible for participation in this study if they: 1. Are ≥18 years on the day of screening 2. Received two doses of SARS-CoV-2 (Biontech/Pfizer, Moderna) vaccine according to recommendations in the label and/or national guidelines. 3. Did develop < 1500 U/ml of SARS-CoV-2 antibodies 4 weeks after second mRNA vaccination 4. A maximum of 12 months after second vaccination 5. Have an understanding of the study, agree to its provisions, and give written informed consent before study entry 6. 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

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 been treated with immunosuppressive therapy within the last 12 months. 3. Received two doses of mRNA SARS-CoV-2 (Biontech/Pfizer or Moderna) vaccine according to recommendations in the label and/or national guidelines. 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, or routine evaluation of humoral response) 5. A maximum of 12 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

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 been treated with immunosuppressive therapy within the last 12 months. 3. Received two doses of mRNA SARS-CoV-2 (Biontech/Pfizer or Moderna) vaccine according to recommendations in the label and/or national guidelines. 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, or routine evaluation of humoral response) 5. A maximum of 12 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