A randomised phase 2 immunogenicity and safety study of a MF59-adjuvanted quadrivalent subunit inactivated cell-derived influenza vaccine (aQIVc) in adults aged 50 years and older

Influenza poses a significant global healthcare burden, with up to 1 billion infections annually, and poorer outcomes in vulnerable populations such as older adults. Vaccination effectiveness is often lower in elderly individuals. By adding an adjuvant and using cell-based vaccine production methods, the MF59-adjuvanted quadrivalent cell-based influenza vaccine (aQIVc) may boost immunogenicity and vaccine effectiveness in this population. We report the results of a randomised proof-of-concept study, investigating the immunogenicity and safety of aQIVc. Eligible participants aged ≥50 years were randomised 1: 1:1:1 to receive aQIVc (n = 116), a non-adjuvanted quadrivalent cell-based influenza vaccine (QIVc; n = 119), an MF59-adjuvanted quadrivalent egg-based influenza vaccine (aQIV; n = 116), or a high-dose quadrivalent recombinant influenza vaccine (QIVr; n = 120). The primary objective was to assess immunogenicity of aQIVc vs the comparators by haemagglutination inhibition (HI) assay 28 days post-vaccination. Secondary objectives included immunogenicity of aQIVc vs comparators 28 days and 180 post-vaccination by microneutralisation assay and 180 days post-vaccination by HI assay; and reactogenicity and safety of all study vaccines. Compared with QIVc and aQIV, aQIVc elicited a higher immune response (adjusted geometric mean titre [GMT] ratio range 1.18-1.85) against all four influenza strains at Day 29. Against QIVr, aQIVc elicited lower responses against A strains (adjusted GMT ratio range 0.79-0.84), and higher responses against B strains (adjusted GMT ratio range 1.15-1.26). Estimated GMT ratios were generally higher in the subgroup of participants aged ≥65 years vs those aged 50-64 years. aQIVc was well tolerated, eliciting similar rates of solicited local adverse events (AE) and slightly higher rates of solicited systemic AE than aQIV, and a higher rate of all solicited AE than QIVc and QIVr. No safety concern was identified. These data support further investigation of additional formulations of aQIVc in adults aged ≥50 years. Clinical trial registry:NCT04576702.