Publication date: Feb 04, 2025

Pediatric hematopoietic cell transplant (HCT) recipients are at high risk for morbidity from influenza virus infection. We demonstrated in a primary phase 2 randomized controlled trial that 2 post-HCT doses of high-dose trivalent influenza vaccine (HD-TIV) given 4 weeks apart were more immunogenic than 2 doses of standard-dose quadrivalent influenza vaccine (SD-QIV). Herein, we present the immunogenicity and safety of influenza vaccination in a consecutive season post-HCT using the same dosing regimen. A subcohort of study participants reenrolled and had hemagglutinin inhibition titers measured at baseline and 4 weeks after each vaccine dose in year 2. We estimated geometric mean fold rise in hemagglutinin inhibition titer from baseline for each group and used linear mixed effects models to estimate adjusted geometric mean ratios (comparing HD-TIV vs SD-QIV) for each antigen at each time point. We described systemic and injection site reactions. A total of 65 subcohort patients participated (33 SD-QIV, 32 HD-TIV). Postvaccine geometric mean fold rise and adjusted geometric mean ratio estimates were higher for both groups following a single influenza vaccine dose in year 2 as compared with 2 doses of the same formulation in year 1. Both groups had similar frequencies of injection site and systemic reactions. A single dose of HD-TIV or SD-QIV was more immunogenic in year 2 than 2 doses of the same formulation in year 1. Reactogenicity was comparable between groups. One dose of influenza vaccine may be sufficient after a 2-dose schedule in the prior year post-HCT. NCT02860039 (ClinicalTrials. gov).

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