Patients with haematol. malignancies (HM) who fall prey to COVID-19, especially those receiving anti-CD20 monoclonal antibodies (mAB), are at a higher risk for complications, mortality, protracted disease, and relapse.Anti-CD-20 mAB became widely used for HM, especially for B-cell non-Hodgkin lymphoma (NHL).Current use of obinutuzumab includes combination with chemotherapy for previously untreated or relapsed follicular lymphoma or chronic lymphocytic leukemia (CLL).Obinutuzumab-based immunochemotherapy and maintenance resulted in more prolonged progression-free survival for patients with advanced-stage follicular lymphoma, at the cost of an increased rate of adverse events, including infections.We performed a single-center population-based cohort study to determine whether patients treated with obinutuzumab were at a higher risk for adverse COVID-19 outcomes than those of rituximab-treated patients.We identified the Omicron variant by either sequencing or when compatible mutations were found in the S gene by Allplex SARS-CoV-2 Master Assay (Seegene, Seoul, South Korea). Follow-up continued until 1 Apr. 1 2022 or death.All patients receiving obinutuzumab in our cohort were treated for indolent lymphomas, most of whom (13/20, 65%) were in the maintenance phase of treatment (6/27, 22% in the rituximab group, p = 0.003).Almost 75% of patients (35/47) in both groups were fully vaccinated (3-4 doses of BNT162b2 vaccine).In conclusion, we observed worse clin. outcomes during Omicron VOC infection in HM patients treated with obinutuzumab.As this treatment has not been shown to increase overall survival when given as maintenance, it may be prudent to defer treatment with obinutuzumab or replace it with a less potent anti- CD20 for the duration of the COVID- 19 pandemic.