Comparison of Two High-Dose Versus Two Standard-Dose Influenza Vaccines in Adult Allogeneic Hematopoietic Cell Transplant Recipients.

Background: Adult hematopoietic cell transplant (HCT) recipients are at high risk for influenza-related morbidity and mortality and have suboptimal influenza vaccine immune responses compared to healthy adults, particularly within 2 years of transplant.

Methods: This phase II, double-blind, multicenter randomized controlled trial compared 2 doses of high-dose trivalent (HD-TIV) to 2 doses of standard-dose quadrivalent (SD-QIV) influenza vaccine administered 1 month apart in adults 3-23 months post-allogeneic HCT. Hemagglutinin antibody inhibition (HAI) titers were measured at baseline, 4 weeks following each vaccine dose, and approximately 7 months post-second vaccination. Injection-site and systemic reactions were assessed for 7 days post-vaccination. The primary immunogenicity comparison was geometric mean HAI titer (GMT) at visit 3 (4 weeks after the second dose); we used linear mixed models to estimate adjusted GMT ratios (aGMRs) comparing HD-TIV/SD-QIV for each antigen.

Results: We randomized 124 adults; 64 received SD-QIV and 60 received HD-TIV. Following the second vaccination, HD-TIV was associated with higher GMTs compared to SD-QIV for A/H3N2 (aGMR = 2.09; 95% confidence interval [CI]: [1.19, 3.68]) and B/Victoria (aGMR = 1.61; 95% CI: [1.00, 2.58]). The increase was not statistically significant for A/H1N1 (aGMR = 1.16; 95% CI: [0.67, 2.02]). There was a trend to more injection-site reactions for HD-TIV after the second vaccination compared to SD-QIV (50% vs 33%; adjusted odds ratio [aOR] = 4.53; 95% CI: [0.71, 28.9]), whereas systemic reactions were similar between groups with both injections.

Conclusions: Adult allogeneic HCT recipients who received 2 doses of HD-TIV produced higher HAI antibody responses for A/H3N2 and B/Victoria compared with 2 doses of SD-QIV, with comparable injection-site or systemic reactions.