Abstract B cell haematological malignancies (HMs) have been described as the worst cancer type for concomitant COVID‐19 in terms of mortality, with rates up to 65%. This risk factor for COVID‐19 cannot only be explained by comorbidities and advanced age of patients, but aggravated by secondary immunodeficiency (SID). We aimed at evaluating the impact of COVID‐19 on 86 HM patients with concomitant SID from a single centre. Only 14 HM patients of 86 (16.28%) patients suffered COVID‐19, with mortality rate of 7%. When we considered patients according to B‐cell defect only or multiple immune defect overlap (B‐T‐cell/NK cells/complement), patients with immune defect overlap presented 5.30‐fold higher risk of COVID‐19 than only B cell defect (95% CI, 1.67–17.0) (p = 0.004). Seven (50%) patients were on active IgRT; while five (36%) had received prior mucosal vaccines for respiratory infections. Our results show that modelling SID in HM may contribute to better prediction of infectious risk and to prompt more targeted and timely preventive therapies.
