Intervention A: patient has received a kidney transplantation full SARS-CoV-2 vaccination with mRNA vaccine (two doses) at least 4 weeks before screening > 18 years of age no SARS-CoV-2 spike protein antibodies at least 4 weeks after the second dose of an mRNA vaccine Substudy A: no SARS-CoV-2 spike protein antibodies four weeks after the third dose Maintenance immunosuppression with mycophenolate or azathioprine Intervention B: Participant has received a kidney transplantation. Participant has received at least two doses of a SARS-CoV-2 vaccine. > 18 years of age. No neutralizing SARS-CoV-2 antibodies at least 4 weeks after the last dose of any SARS-CoV-2 vaccine.

Intervention A: patient has received a kidney transplantation full SARS-CoV-2 vaccination with mRNA vaccine (two doses) at least 4 weeks before screening > 18 years of age no SARS-CoV-2 spike protein antibodies at least 4 weeks after the second dose of an mRNA vaccine Substudy A: no SARS-CoV-2 spike protein antibodies four weeks after the third dose Maintenance immunosuppression with mycophenolate or azathioprine Intervention B: Participant has received a kidney transplantation. Participant has received at least two doses of a SARS-CoV-2 vaccine. > 18 years of age. No neutralizing SARS-CoV-2 antibodies at least 4 weeks after the last dose of any SARS-CoV-2 vaccine.

patient has received a kidney transplantation full SARS-CoV-2 vaccination with mRNA vaccine (two doses) at least 4 weeks before screening > 18 years of age no SARS-CoV-2 spike protein antibodies at least 4 weeks after the second dose of an mRNA vaccine

patient has received a kidney transplantation full SARS-CoV-2 vaccination with mRNA vaccine (two doses) at least 4 weeks before screening > 18 years of age no SARS-CoV-2 spike protein antibodies at least 4 weeks after the second dose of an mRNA vaccine

patient has received a kidney transplantation full SARS-CoV-2 vaccination with mRNA vaccine (two doses) at least 4 weeks before screening > 18 years of age no SARS-CoV-2 spike protein antibodies at least 4 weeks after the second dose of an mRNA vaccine Substudy A: no SARS-CoV-2 spike protein antibodies four weeks after the third dose Maintenance immunosuppression with mycophenolate or azathioprine

patient has received a kidney transplantation full SARS-CoV-2 vaccination with mRNA vaccine (two doses) at least 4 weeks before screening > 18 years of age no SARS-CoV-2 spike protein antibodies at least 4 weeks after the second dose of an mRNA vaccine Substudy A: no SARS-CoV-2 spike protein antibodies four weeks after the third dose Maintenance immunosuppression with mycophenolate or azathioprine

patient has received a kidney transplantation full SARS-CoV-2 vaccination with mRNA vaccine (two doses) at least 4 weeks before screening > 18 years of age no SARS-CoV-2 spike protein antibodies at least 4 weeks after the second dose of an mRNA vaccine

patient has received a kidney transplantation full SARS-CoV-2 vaccination with mRNA vaccine (two doses) at least 4 weeks before screening > 18 years of age no SARS-CoV-2 spike protein antibodies at least 4 weeks after the second dose of an mRNA vaccine