Aged <18 years or >80 years Multi-organ transplant recipients (e.g. kidney-pancreas) Patients who are currently pregnant Patient has an underlying condition predisposing to increased gut permeability (including, but not limited to: active or recent within 6 weeks gastrointestinal infection, inflammatory bowel disease, short-gut syndrome, or coeliac disease) Have not received 2 doses of a COVID-19 vaccine regimen (either adenoviral vector or mRNA-based) Have received 2 doses of a COVID-19 vaccine regimen (either adenoviral vector or mRNA-based) and have mounted an adequate immune response (anti-spike protein antibodies above detection threshold)

Aged <18 years or >80 years Multi-organ transplant recipients (e.g. kidney-pancreas) Patients who are currently pregnant Patient has an underlying condition predisposing to increased gut permeability (including, but not limited to: active or recent within 6 weeks gastrointestinal infection, inflammatory bowel disease, short-gut syndrome, or coeliac disease) Have not received 2 doses of a COVID-19 vaccine regimen (either adenoviral vector or mRNA-based) Have received 2 doses of a COVID-19 vaccine regimen (either adenoviral vector or mRNA-based) and have mounted an adequate immune response (anti-spike protein antibodies above detection threshold)