Multivariable regression analysis.

Patients with plasma cell disorders (PCD) are at an increased risk for severe morbidity and mortality due to COVID-19. Recent data have suggested that patients with hematological malignancies, including those with PCD, have suboptimal antibody response to COVID-19 vaccination. We compared the antibody titers of 213 patients with PCD to those of 213 immunocompetent healthcare workers after the second vaccine dose of the BNT162b2 mRNA vaccine. Blood samples were taken 2–4 weeks after the second vaccination and analyzed for anti-receptor binding-domain immunoglobulin G (RBD-IgG) antibodies and neutralizing antibodies (NA). At a median of 20 days after the second vaccine dose, 172 patients (80.8%) developed anti-RBD-IgG antibodies with a geometric mean titer (GMT) of 2.7 (95% confidence interval [CI], 2.4–3.1). In the control group 210 (98.9%) developed anti-RBD-IgG antibodies after a median of 21 days, with a GMT of 5.17 (95%CI, 4.8–5.6), p