A Randomized Trial of One versus Two Doses of Influenza Vaccine after Allogeneic Transplantation

Influenza infection after allogeneic hematopoietic cell transplantation (allo-HCT) can result in severe complications. The effectiveness of the annual vaccine depends on age, immune competence, and the antigenic potential of the 3 strains included. We hypothesized that a second vaccine dose, the standard of care for vaccine-naïve children, might improve post hematopoietic cell transplantation (HCT) immune responses. Patients >60 days post-HCT were randomized to receive either 1 (n = 33) or 2 (n = 32) influenza vaccine doses separated by 1 month. The primary endpoint was whether 2 vaccinations induced superior immunity; however, we found no difference. Secondary endpoints were to identify variables associated with responses. Both hemagglutination inhibition (HI; P < .005) and ELISpot responses (P = .03) were greater for patients vaccinated ≥1 year posttransplantation. Umbilical cord blood (UCB) recipients showed less IFN-γ responses (P < .001). Interestingly, there was a positive correlation between the total number of CD19+ cells before vaccination and seroconversion (P = .01) and an inverse correlation for IFN-γ responses (P = .05). Variables not associated with vaccine responses included prevaccine CD4+ cell counts (total, naïve, or memory), steroid usage at vaccination, age, or conditioning intensity. Time from transplantation to vaccination and absolute CD19+ cell counts were the strongest predictors of vaccine responses. Methods to improve influenza vaccine responses after allo-HCT are needed.