Responses to live attenuated influenza vaccine in children vaccinated previously with Pandemrix (ASO3

We report a phase III/IV open-label study on the immunogenicity of a single dose of a Live Attenuated Influenza Vaccine (LAIV) (Fluenz™) in children naïve to, or in previous receipt of, AS03Eligible children were enrolled to receive qLAIV and stratified according to previous Pandemrix™ vaccination. Functional antibody for the vaccine strains were analysed using Haemagglutination Inhibition (HAI); in addition antibodies to the A/H1N1pdm09 strain were measured by Neuraminidase Antibody Inhibition (NAI) and neutralisation assays. Fourfold titre increases by HAI were observed for 39% (95% confidence interval 33-46%) and 43% (37-51%) of subjects for the two influenza B vaccine strains and 8% (5-13%) for the A/H3N2 strain with no significant differences between the Pandemrix™ naïve or previously vaccinated groups in antibody tites pre- or post-vaccination or seroconversion rates. In both groups, the response to the qLAIV A/H1N1pdm09 component was barely detectable, overall HAI seroconversion rate 1.8% (0.5-4.7%). Previous receipt of Pandemrix™ was associated with significantly higher levels of A/H1N1pdm09 neutralising antibody, but decreased NAI titres pre-vaccination, with the differences maintained post-vaccination.Previous receipt of Pandemrix™ has had a significant impact on the influenza immune status of children several years later. Higher levels of neutralising antibody to A/H1N1pdm09 pre- and post-vaccination, but significantly lower levels of antibody to NA, were observed compared with Pandemrix™-naïve children, while responses to influenza B and A/H3N2 and antibody levels prior to vaccination were similar in both groups. This suggests that early vaccination with a powerful adjuvant maintains functional immunity for several years, which prevents natural infection. Alternatively, the AS03