Inclusion Criteria:  Be aged 18 years or older Have given written informed consent  Be a member of one of the following vulnerable patients populations  Dialysis - including in centre haemodialysis, home haemodialysis and peritoneal dialysis Kidney transplant receiving at least one of the immunosuppressive medications listed below Vasculitis (according to Chapel Hill Consensus Conference 2012 definitions) receiving at least one of the immunosuppressive medications listed below Glomerulonephritis* receiving at least one of the immunosuppressive medications listed below Ciclosporin Tacrolimus Azathioprine Mycophenolate Mofetil or Mycophenolic Acid Belatacept Methotrexate Tocilizumab Abatacept Leflunomide Prednisolone (current dose) > 20mg daily for 8 weeks Anti-TNF (infliximab, adalimumab, etanercept) Belimumab Cyclophosphamide (within the last 6 months) Rituximab (in the last 12 months) Alemtuzumab (in the last 12 months)  Exclusion Criteria:  Inability to provide informed consent or to comply with trial procedures COVID-19 at time of enrolment - either positive SARS CoV-2 swab (PCR) or symptoms highly suggestive of COVID-19 infection Known chronic liver disease or hepatic dysfunction as evidenced by ALT or AST > 3x upper limit of the normal range Allergy to niclosamide or history of significant adverse reaction to niclosamide or related compounds, or to any of the excipients used Significant structural nasal disease in the opinion of the investigator Pregnant, trying to conceive, unwilling to use contraception or breastfeeding  Participation in another interventional prophylactic or vaccine trial* against COVID-19  Patients remain eligible for enrolment if they have received SARS-COV-2 vaccination as part of routine care.