Clinical Effectiveness of Influenza Vaccination After Allogeneic Hematopoietic Stem Cell Transplantation: A Cross-sectional, Prospective, Observational Study

Background Vaccination is the primary method for preventing influenza respiratory virus infection (RVI). Although the influenza vaccine is able to achieve serological responses in some allogeneic hematopoietic stem cell transplantation (allo-HSCT) recipients, its clinical benefits are still uncertain. Methods In this prospective, cross-sectional study, we retrospectively analyzed the effect of inactivated trivalent influenza vaccination on the prevalence of influenza RVI in a consecutive cohort of 136 allo-HSCT adult recipients who developed 161 RVI over 5 flu seasons (from 2013 to 2018). Respiratory viruses in upper- and/or lower-respiratory tract specimens were tested using multiplex polymerase chain reaction panel assays. Results Overall, we diagnosed 74 episodes (46%) of influenza RVI in 70 allo-HSCT recipients. Influenza RVI occurred in 51% of the non-vaccinated compared to 36% of the vaccinated recipients (P = .036). A multivariate analysis showed that influenza vaccination was associated with a lower prevalence of influenza RVI (odds ratio [OR] 0.39, P = .01). A multivariate risk factor analysis of lower-respiratory tract disease (LRTD) identified 2 conditions associated with the probability of influenza RVI progression: influenza vaccination (OR 0.12, 95% confidence interval [CI] 0.014-1, P = .05) and a high-risk immunodeficiency score (OR 36, 95% CI 2.26-575, P = .011). Influenza vaccination was also associated with a lower likelihood of an influenza-related hospital admission (14% vs 2%, P = .04). Conclusions This study shows that influenza vaccination may have a clinical benefit in allo-HSCT recipients with virologically-confirmed RVI, in terms of a lower influenza RVI prevalence, slower LRTD progression, and lower likelihood of hospital admission. Influenza vaccination after allogeneic hematopoietic stem cell reciept was associated with a lower prevalence of influenza respiratory virus infection (RVI) among recipients with virologically-confirmed RVIs. Vaccination and a high-risk immunodeficiency score impacted influenza virus lower-respiratory tract disease progression.