Serum IgM levels independently predict immune response to influenza vaccine in long-term survivors vaccinated at >1 year after undergoing allogeneic hematopoietic stem cell transplantation.

Influenza virus infection can cause fatal complications (e.g., pneumonia) in immunodeficient long-term survivors of allogeneic hematopoietic stem cell transplantation (allo-HSCT). The immune response to the vaccine improves if it is administered at >1 year after allo-HSCT, although the response may vary according to the patient's immune status. We sought to identify predictors of immune response to trivalent inactivated influenza vaccine (TIV) among patients vaccinated at >1 year after allo-HSCT. We included 27 allo-HSCT recipients, with a median interval of 4.3 years (range 1.0-10.1 years) from transplantation to vaccination. Nineteen patients achieved a response to TIV, although a low immune response to TIV was significantly associated with calcineurin inhibitor treatment, and moderate chronic graft-versus-host disease and IgM levels of <0.5 g/L at the time of vaccination. Multivariate analysis revealed that IgM levels of <0.5 g/L at the vaccination were an independent predictor of a low immune response to TIV. These results indicate that a more effective approach is needed to induce a vaccine-specific immune response among long-term survivors of allo-HSCT who have low serum IgM levels.