Phase 3 RCT evaluating immunogenicity and safety of a novel MF59-adjuvanted, cell-derived, higher-dose quadrivalent influenza vaccine (aQIVc; 45 µg HA/strain + MF59) versus MF59-adjuvanted egg-derived QIV (aQIV; 15 µg HA/strain + MF59) and recombinant QIV (QIVr; 45 µg HA/strain) in 7,677 adults aged ≥50 years, with day-29 immunogenicity as the primary endpoint.
aQIVc met lot-to-lot consistency criteria and was superior to aQIV for all 4 strains (GMT ratios: 1.53 for A/H1N1, 1.22 for A/H3N2, 1.73 for B/Victoria, 1.71 for B/Yamagata). Non-inferiority versus QIVr was met for A/H1N1, B/Victoria, and B/Yamagata, but not A/H3N2 (GMT ratio 0.69, 97.5% CI 0.65–0.74). Serious adverse events were low and comparable across groups (~2.8–3.5%).
Non-inferiority to QIVr was not met for A/H3N2, suggesting a potential immunogenicity gap for this strain versus recombinant vaccine. The trial was conducted over a single influenza season (2023–24), and clinical efficacy against influenza illness was not assessed. The study population was restricted to healthy adults, limiting generalisability to those with comorbidities.
aQIVc offers a stronger immune response than standard-dose adjuvanted influenza vaccine for all four strains in adults ≥50, but clinicians should note it did not match QIVr for A/H3N2. Safety was acceptable with mostly mild-to-moderate, transient local and systemic reactions.
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