Summary: Prolonged SARS‐CoV‐2 infection in immunocompromised individuals has been scattered, but the details remain unclear. We conducted a prospective study with 26 COVID‐19 patients with haematological malignancies to determine viral shedding kinetics and characteristics. We obtained nasopharyngeal swabs from the patients 21–28 days post‐onset for a PCR test and performed virus isolation from the PCR‐positive samples. A viable virus was detected in five patients (19.2%), all of whom had malignant lymphoma. Those patients had significantly lower CD4+ T‐cell counts than the PCR‐negative patients. A comparison of previous chemotherapy showed that anti‐CD20 antibodies and bendamustine may be risk factors for prolonged viral shedding. [ABSTRACT FROM AUTHOR]