CSL Seqirus’ aQIVc showed stronger immune responses than an adjuvanted egg-based influenza vaccine in a Phase 3 study of adults aged 50 and older.
Written By: Aasritha Thippavajjala, PharmD
Reviewed By: Pharmacally Editorial Team
The Phase 3 study (NCT06015282), published in The Lancet Infectious Diseases, evaluated aQIVc in adults aged 50 years and older, comparing it with an MF59-adjuvanted egg-derived quadrivalent influenza vaccine (aQIV) and a recombinant quadrivalent influenza vaccine (QIVr). The trial assessed immunogenicity, safety and lot-to-lot manufacturing consistency.
The randomized, observer-blind study enrolled 7,699 healthy adults across Canada, Denmark, Estonia, Germany, Pakistan, the Philippines, the UK and the US. Participants received a single intramuscular dose of aQIVc, aQIV or QIVr.
Stronger Responses Across Four Influenza Strains
aQIVc met all predefined lot-to-lot consistency criteria for three manufacturing batches.
At day 29, aQIVc produced higher geometric mean antibody titres than aQIV against all four strains. GMT ratios were 1.53 for A/H1N1, 1.22 for A/H3N2, 1.73 for B/Victoria and 1.71 for B/Yamagata.
Seroconversion also favored aQIVc, with differences of 16.8, 9.5, 21.9 and 24.3 percentage points for A/H1N1, A/H3N2, B/Victoria and B/Yamagata, respectively.
Against QIVr, aQIVc met non-inferiority criteria for A/H1N1 and both B strains, but not A/H3N2. The A/H3N2 GMT ratio was 0.69, with a 97.5% CI of 0.65 to 0.74, while the seroconversion difference was −7.4 percentage points.
The study also reported exploratory findings showing enhanced neuraminidase antibody responses with aQIVc. The clinical relevance of neuraminidase antibodies remains an area of ongoing influenza research.
Three Vaccine Approaches in One Formulation
aQIVc contains 45 μg of haemagglutinin per strain and 19.5 mg of MF59 squalene per dose. The aQIV comparator contained 15 μg of haemagglutinin per strain and 9.75 mg of MF59.
The vaccine combines cell-based manufacturing, MF59 adjuvantation and higher antigen content. Cell-based production avoids egg-based virus propagation, while MF59 enhances the magnitude and breadth of the immune response. The higher antigen dose provides three times the haemagglutinin content of the conventional-dose aQIV comparator.
This approach is particularly relevant in older adults, in whom immune responses to influenza vaccination can decline with age.
Quadrivalent Trial, Trivalent Regulatory Product
An important distinction is that the Phase 3 study evaluated the quadrivalent aQIVc formulation, which contained A/H1N1, A/H3N2, B/Victoria and B/Yamagata antigens. However, the product subsequently advanced through European and UK regulatory pathways as a trivalent formulation, marketed as AUJEMFLU.
The change reflects the global move away from B/Yamagata-containing influenza vaccines following WHO recommendations. CSL Seqirus removed the B/Yamagata antigen from the final formulation, resulting in the trivalent product containing A/H1N1, A/H3N2 and B/Victoria.
The EMA issued the marketing authorization for AUJEMFLU on August 20, 2026, for prevention of influenza in adults aged 50 years and older.
Thus, the four-strain immunogenicity results reported in the Phase 3 publication reflect the earlier quadrivalent clinical-development formulation, while the currently authorized European product is trivalent.
Safety Profile Remained Acceptable
aQIVc produced more local and systemic adverse events than the comparator vaccines, but most were mild to moderate, transient and self-resolving.
Serious adverse events through day 181 occurred in 2.8% of participants receiving aQIVc, compared with 3.5% with aQIV and 2.9% with QIVr. The investigators identified no safety concerns.
Regulatory and Clinical Development Continues
The Phase 3 findings provide clinical evidence for combining cell-based manufacturing, MF59 adjuvantation and higher antigen content in an influenza vaccine for adults aged 50 years and older.
With the regulatory pathway now centered on the trivalent formulation, future use of the technology will depend on national immunization recommendations, regulatory decisions and market-access pathways. In the UK, all influenza vaccines used for the 2026–27 season are trivalent following the removal of B/Yamagata from future vaccine formulations.
Reference
Brandon J Essink, MD et al, Immunogenicity and safety of an MF59-adjuvanted cell-derived higher-dose quadrivalent influenza vaccine (aQIVc) in adults aged 50 years or older: a phase 3 randomised controlled trial, The Lancet Infectious Diseases, September 10, 2026, https://doi.org/10.1016/S1473-3099(26)00410-X
Lancet Publication Marks Important Advance in Influenza Prevention for Older Adults, CSL, 10 September 2026
The Celljuvant Study: A Phase 3 Immunogenicity and Safety Study of aQIVc Vaccine in Adults Aged 50 Years and Older, ClinicalTrials.gov ID NCT06015282
About the Writer
Aasritha Thippavajjala (Linkedin) is a pharm D student and aspiring medical writer with medical writing, clinical training experience and a strong interest in clinical research and patient safety She has hands-on exposure to clinical pharmacy activities including medication profile assessment, clinical case review, identification of potential drug-related problems, ADR awareness, patient counselling, and clinical documentation. She has also gained experience in medical literature review, evidence synthesis, and scientific communication through her published review article on digital twin-based patient simulation and her poster presentation at the 74th Indian Pharmaceutical Congress. Certified in ICH Good Clinical Practice (E6(R3)) and Scientific Writing in Health Research, she is passionate about applying her clinical knowledge and research skills to medical writing ,clinical research and contributing to accurate, evidence-based healthcare.