Immunogenicity of the inactivated influenza vaccine in children who have undergone allogeneic haematopoietic stem cell transplant.

Influenza vaccination is recommended for children following allogeneic haematopoietic stem cell transplant (HSCT), however there is limited evidence regarding its benefit. A prospective multicentre study was conducted to evaluate the immunogenicity of the inactivated influenza vaccine in children who have undergone HSCT compared with healthy age-matched controls. Participants were vaccinated between 2013 and 2016 according to Australian guidelines. Influenza-specific hemagglutinin inhibition antibody titres were performed prior to each vaccination and 4 weeks following the final vaccination. A nasopharyngeal aspirate for influenza was performed on participants that developed influenza-like illness. There were 86 children recruited; 43 who had undergone HSCT and 43 controls. For the HSCT group, seroprotection and seroconversion rates were 81.4% and 60.5% for H3N2, 41.9% and 32.6% for H1N1, and 44.2% and 39.5% for B strain respectively. There was a significant geometric mean fold increase to the H3N2 (GMFI 5.80, 95% CI 3.68-9.14, p < 0.001) and B (GMFI 3.44, 95% CI 2.36-5.00, p = 0.048) strains. Serological response was superior in age-matched controls to all vaccine strains. There were no serious adverse events following vaccination. For children who underwent HSCT, incidence of laboratory-proven influenza infection was 2.3%. Overall, this study provides evidence to support annual inactivated influenza vaccine administration to children following HSCT.