Influenza A haemagglutinin specific IgG responses in children and adults after seasonal trivalent live attenuated influenza vaccination

Plasma was collected from 20 children and 20 adults pre- and post-LAIV3 vaccination (up to a year) and analysed by the haemagglutination inhibition (HI) and ELISA assays. We found that LAIV3 boosted the HA specific IgG response against the head and the full-length of H3N2 in children, but not adults. Adults had higher levels of pre-existing stalk antibodies (towards H3N2 and H1N1), but these were not boosted by LAIV3. Importantly, we observed a trend in boosting of H1N1 HA stalk specific antibodies in children after LAIV3. Whereas, heterosubtypic H5 and H7 full-length HA specific antibodies were not boosted in either children or adults. In conclusion, LAIV3 elicited H3-head and low levels of H1 stalk specific antibody responses in children, supporting the prophylactic use of LAIV in children.