LAUSR

Patients with B‐cell malignancies have suboptimal immune responses to SARS‐CoV‐2 vaccination and are a high‐risk population for severe COVID19 disease. We evaluated the effect of a third booster BNT162b2 vaccine on the kinetics of anti‐ SARS‐CoV‐2 neutralizing antibody (NAbs) titers in patients with B‐cell malignancies. Patients with NHL (n = 54) Waldenström's macroglobulinemia (n = 90) and chronic lymphocytic leukemia (n = 49) enrolled in the ongoing NCT04743388 study and compared against matched healthy controls. All patient groups had significantly lower NAbs compared to controls at all time points. 1 month post the third dose (M1P3D) NAbs increased significantly compared to previous time points (median NAbs 77.9%, p < .05 for all comparisons) in all patients. NAbs ≥ 50% were seen in 59.1% of patients, 34.5% of patients with suboptimal responses post‐second dose, elicited a protective NAb titer ≥50%. Active treatment, rituximab, and BTKi treatment were the most important prognostic factors for a poor NAb response at 1MP3D; only 25.8% of patients on active treatment had NAbs ≥ 50%. No significant between‐group differences were observed. Patients with B‐cell malignancies have inferior humoral responses against SARS‐CoV‐2 and booster dose enhances the NAb response in a proportion of these patients.