Vaccination against pandemic H1N1 (2009) in patients after allogeneic hematopoietic stem cell transplantation: a retrospective analysis.

PURPOSE Limited data are available on immunologic responses to primary pandemic H1N1 (2009) vaccination in recipients of allogeneic hematopoietic stem cell transplantation (HSCT) recipients. In 2009 serologic responses to either pandemic H1N1 (2009) vaccine (n = 36) or pandemic H1N1 (2009) infection (n = 2) were studied in 38 HSCT recipients. METHODS Responses were measured with a standard hemagglutination-inhibition assay. Fourteen patients had active chronic graft-versus-host disease (cGvHD) at the time of vaccination/infection and seven patients had cGvHD in remission; 11 patients had no immunosuppressive therapy, and 27 patients were on immunosuppressive therapy. Nineteen patients (53%) responded to pandemic H1N1 (2009) vaccination. Two patients had pandemic H1N1 (2009) infection without prior vaccination, and one patient had severe pandemic H1N1 (2009) infection with acute respiratory distress syndrome despite prior single vaccination. RESULTS Non-responders to pandemic H1N1 (2009) vaccination more often had cGvHD (65 vs. 53%) and received second- or third-line therapy (53 vs. 11%), while responders mostly had first-line therapy for cGvHD. While vaccine responders had no or single agent immunosuppressive therapy, non-responders frequently received moderate or intense immunosuppressive therapy. All vaccine recipients previously treated with rituximab were non-responders. CONCLUSIONS In summary, the overall response to pandemic H1N1 (2009) vaccination in HSCT recipients was modest. Patients receiving combined immunosuppressive therapy for steroid-refractory cGvHD barely responded to pandemic H1N1 (2009) vaccination.