BACKGROUNDThe role of antibodies in coronavirus disease 2019 (COVID-19) in patients with X-linked agammaglobulinaemia (XLA) has yet to be characterised and clinical courses observed in this cohort of patients have been heterogeneous. Whilst some exhibit spontaneous recovery, others have experienced a more protracted disease length. Previous reports have described successful use of convalescent plasma, however there is a paucity of information around the use of the REGN-COV2 antibody cocktail in these patients. CASE REPORTA patient with XLA was admitted to hospital with COVID-19 and remained persistently symptomatic with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) swab positivity despite treatment with Remdesivir and dexamethasone. Attempts at modulating the immune response with anakinra were unsuccessful. Consent for compassionate use of REGN-COV2 was obtained with administration taking place on day 87 of his illness. This was followed by a period of convalescence and SARS-CoV-2 nasopharyngeal swab negativity. As a consequence of prolonged immunosuppression, the patient developed pneumocystis pneumonia. CONCLUSIONThis case highlights the role of antibodies in clearing SARS-CoV-2 in a hypogammaglobulinaemic host and demonstrates the consequences of prolonged immunosuppression and delayed treatment. We propose that this may be of particular significance given the capacity of SARS-CoV-2 to develop advantageous mutations in a chronically infected host.