Immunogenicity of a monovalent influenza A(H1N1)pdm09 vaccine in patients with hematological malignancies.

Patients with hematological malignancies have high risk for morbidity and mortality from influenza. This study was conducted to evaluate the immunogenicity and reactogenicity of an influenza A(H1N1)pdm09 vaccine among such subjects. Fifty subjects were vaccinated twice during the 2009-2010 season. The antibody response was expressed in terms of mean fold rise (MFR) of geometric mean titer, seroresponse proportion (sR), and seroprotection proportion (sP). The first vaccination induced only a small response, and additional antibody was acquired after the second dose (MFR 2.3 and 3.9, sR 32% and 54%, and sP 30% and 48% after the first and the second vaccination, respectively). Rituximab treatment showed an especially inhibitory effect (MFR 1.3, sR 9% and sP 0%). When analyzed using logistic regression models, only rituximab was found to have an independent effect; the adjusted odds ratio for sR was 0.09 (P = 0.05). Influenza vaccination of patients with hematological malignancies resulted in adepuate response, and the second vaccination induced additional antibody. It is therefore recommended to vaccinate this group twice.