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

Ryan, Anne L.; Wadia, Ushma D.; Jacoby, Peter; Cheung, Laurence C.; Kerr, Fiona; Fraser, Chris; Tapp, Heather; Mechinaud, Francoise; Carolan, Louise A.; Laurie, Karen L.; Barr, Ian G.; Blyth, Christopher C.; Gottardo, Nicholas G.; Richmond, Peter C.; Kotecha, Rishi S.

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.