Responses to live attenuated influenza vaccine in children vaccinated previously with Pandemrix (ASO3B adjuvanted pandemic A/H1N1pdm09)

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 AS03B adjuvant may have re-directed the immune response, with focus towards viral HA and away from viral NA.