Randomized Controlled Trial of High‐Dose Intradermal Versus Standard‐Dose Intramuscular Influenza Vaccine in Organ Transplant Recipients

The immunogenicity of standard intramuscular (IM) influenza vaccine is suboptimal in transplant recipients. Also, recent studies suggest that alloantibody may be upregulated due to vaccination. We evaluated a novel high‐dose intradermal (ID) vaccine strategy. In conjunction, we assessed alloimmunity. Transplant recipients were randomized to receive IM or high‐dose ID vaccine. Strain‐specific serology and HLA alloantibody production was determined pre‐ and postimmunization. In 212 evaluable patients (105 IM, 107 ID), seroprotection to H1N1, H3N2 and B strains was 70.5%, 63.8% and 52.4% in the IM group, and 71.0%, 70.1%, 63.6% in the ID group (p = ns). Seroconversion to ≥1 antigen was 46.7% and 51.4% in the IM and ID groups respectively (p = 0.49). Response was more likely in those ≥6 months posttransplant (53.2% vs. 19.2%; p = 0.001). Use of mycophenolate mofetil was inversely associated with vaccine response in a dose‐dependent manner (p < 0.001). Certain organ subgroups had higher response rates for influenza B in the ID vaccine group. Differences in anti‐HLA antibody production were detected in only 3/212(1.4%) patients with no clinical consequences. High‐dose intradermal vaccine is an alternative to standard vaccine and has potential enhanced immunogenicity in certain subgroups. In this large cohort, we also show that seasonal influenza does not result in significant alloantibody production.