Pandemic and seasonal H1N1 influenza hemagglutinin-specific T cell responses elicited by seasonal influenza vaccination

Understanding whether seasonal influenza vaccines can elicit antibody and T cell responses against the 2009 pandemic H1N1 strain is important. We compared T cell and antibody responses elicited by trivalent inactivated influenza vaccine (TIV) and live attenuated influenza vaccine (LAIV) in healthy adults. Both vaccines boosted pre-existing T cells to the seasonal and pandemic hemagglutinin (HA) but responses were significantly greater following immunization with LAIV. Antibody titers were significantly boosted only by TIV. The relationship between antibody and T cell responses and the effect of the magnitude of pre-existing immunity on vaccine-induced responses were also evaluated. Cross reactive T cell responses to the pandemic H1N1 HA existed among the cohort before the circulation of the virus to varying degrees and these responses were boosted by seasonal vaccination.