Inactivated seasonal influenza vaccines with enhanced immunogenicity recommended in older adults. An 11-arm randomized controlled trial was conducted from 2017-2021 to investigate whether annual receipt of MF59-adjuvated, high-dose HA or recombinant HA vaccines and alternating vaccine schedules may increase immune responses compared to receipt of standard influenza vaccine in older adults (65-82 years) in Hong Kong (n=1861). Antibody function including Fc receptor binding, avidity and IgG subclass (IgG1, 2, 3, 4) usage, and T cell responses including phenotype and polyfunctionality against vaccine representative proteins were assessed at baseline, days 7 and 30 post-vaccination longitudinally over 4 years. Adjuvanted vaccines also had an advantage of reduced antibody waning by 1 year post vaccination, increased HA-stem specific responses, avidity and FcR binding. Furthermore, there were year on year gains in antibody boosting for adjuvanted vaccine recipients. All vaccines enhanced recall of activated memory Tfh cells, which also correlated with increased plasmablast activity and superior antibody avidity responses in the adjuvanted vaccine group. There was diminished T cell boosting in later study years, with boosting by adjuvanted and high dose vaccines maintained in some subsets and specificities by year 4. Animal protection studies showed adjuvanted and high dose vaccines showed accelerated viral clearance. A better understanding for correlates of protective immunity beyond HI antibodies is needed to enable rational targeting of vaccination strategies in older adults.