Randomized-controlled trial comparing homologous (mRNA vaccine) vs. heterologous (vector vaccine) for third SARS-CoV-2 vaccine dose in kidney transplant recipients not responding to initial prime-boost vaccination with an mRNA vaccine.

Inclusion Criteria:

• 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

Exclusion Criteria:

• acute illness with fever
• Prior documented infection with SARS-CoV-2
• triple anticoagulation therapy
• Subject is currently enrolled in or has not yet completed at least 30 days since ending other investigational device or drug trial(s), or subject is receiving other investigational agent(s)
• Subject has known sensitivity or intolerance to any of the products to be administered for the purpose of this study
• Subject has any kind of disorder that compromises the ability of the subject to give written informed consent and/or to comply with the study procedures
• Subject is pregnant or breast feeding