A 39-year-old woman with systemic lupus erythematosus treated with anti-CD20 monoclonal antibody rituximab was admitted to our hospital with COVID-19 pneumonia. Despite receiving dexamethasone, she developed hypoxaemia and persistent lung opacities. As bronchoalveolar lavage was suggestive of cryptogenic organising pneumonia, high-dose corticosteroid was administered, and she received antimicrobial therapy for opportunistic infections without improvement. Reverse transcription PCR was repeatedly positive for SARS-CoV-2, and virus replication was confirmed in cell cultures. As no anti-SARS-CoV-2 antibodies were detected more than 100 days after symptom onset, she was treated with convalescent plasma with fast clinical improvement, returning home days later. Our case shows that persistent SARS-CoV-2 infection in an immunocompromised patient may be overturned with the appropriate treatment.