Selection of an adjuvant for seasonal influenza vaccine in elderly people: modelling immunogenicity from a randomized trial

Background: Improved influenza vaccines are needed to reduce influenza-associated complications in older adults. The aim of this study was to identify the optimal formulation of adjuvanted seasonal influenza vaccine for use in elderly people. Methods: This observer-blind, randomized study assessed the optimal formulation of adjuvanted seasonal influenza vaccine based on immunogenicity and safety in participants aged >= 65 years. Participants were randomized (similar to 200 per group) to receive one dose of non-adjuvanted vaccine or one of eight formulations of vaccine formulated with a squalene and tocopherol oil-in-water emulsion-based Adjuvant System (AS03(C), AS03(B) or AS03(A), with 2.97, 5.93 and 11.86 mg tocopherol, respectivel Results: In the HI antibody-based model, an AS03 dose-response was evident; responses against the A/H1N1 and A/H3N2 strains were higher for all adjuvanted formulations versus non-adjuvanted vaccine, and for the AS03(A)-MPL25, AS03(B)-MPL25 and AS03(B)-MPL50 formulations against the B strain. Modelling using more stringent criteria (post hoc) showed a clear dose-range effect for the AS03 component against all strains, whereas MPL showed a limited effect. Higher T-cell responses for adjuvanted ver Conclusions: Five formulations containing AS03(A) or AS03(B) were identified as potential candidates to improve immune responses to influenza vaccination; AS03(B) without MPL showed the best balance between improved immunogenicity and acceptable reactogenicity.