- Multi-organ transplant recipients (e.g. kidney-pancreas) - Aged <18 years or >70 years - Significant kidney dysfunction, estimated GFR =25 mL/min or spot urinary albumin:creatinine ratio =100 mg/µmol - Unable or unwilling to provide informed consent to participate in the trial - Have received 2 doses of a COVID-19 vaccine regimen (either adenoviral vector or mRNA-based) and have mounted an adequate immune response (anti-Receptor Binding Domain antibodies >100 U/mL) - Have had documented infection with COVID-19 - Known allergy to or intolerance of sirolimus or everolimus - Patients who are currently pregnant

- Multi-organ transplant recipients (e.g. kidney-pancreas) - Aged <18 years or >70 years - Significant kidney dysfunction, estimated GFR =25 mL/min or spot urinary albumin:creatinine ratio =100 mg/µmol - Unable or unwilling to provide informed consent to participate in the trial - Have received 2 doses of a COVID-19 vaccine regimen (either adenoviral vector or mRNA-based) and have mounted an adequate immune response (anti-Receptor Binding Domain antibodies >100 U/mL) - Have had documented infection with COVID-19 - Known allergy to or intolerance of sirolimus or everolimus - Patients who are currently pregnant