Trivalent inactivated influenza vaccines induce broad immunological reactivity to both internal virion components and influenza surface proteins

► Mouse models of influenza vaccination were used to evaluate CD4+ T cell specificity. ► Licensed split influenza vaccines elicit CD4+ T cells of diverse specificity. ► HA, NA, M1, NP and NS1 reactive CD4+ T cells were elicited after primary vaccination. ► Vaccination continually boosts and maintains an extremely diverse CD4 repertoire.