CSL Seqirus Unveils Advanced Flu Vaccine After Decades of R&D

MAIDENHEAD, UK – September 10, 2026 – In a move that underscores a long-term strategic commitment to vaccine innovation, CSL Seqirus today announced the publication of pivotal Phase 3 study results for a new influenza vaccine designed specifically for older adults. The publication in the prestigious journal The Lancet Infectious Diseases validates a novel approach that combines three distinct, proven technologies into a single shot, marking a significant milestone for the company and a potential paradigm shift in influenza prevention for a vulnerable, growing demographic.

The vaccine, known as aQIVc, is the culmination of decades of research and development by the CSL business unit, one of the world's largest influenza vaccine providers. It aims to address a persistent public health challenge: the reduced effectiveness of standard flu vaccines in people aged 50 and over, whose immune systems naturally weaken with age. By synergizing multiple advanced technologies, CSL Seqirus is making a calculated bet that superior protection will drive both public health outcomes and market leadership in an increasingly competitive space.

A Scientific Trifecta to Counteract Immune Decline

The core of CSL Seqirus's strategy lies in the vaccine's unique "triple-threat" formulation. For the first time, a single influenza vaccine integrates an adjuvant, cell-based manufacturing, and a higher antigen dose—each a recognized method for boosting immune response, but never before combined.

The Phase 3 study, which enrolled nearly 7,700 adults across eight countries, provides the first large-scale evidence of this combination's power. The results demonstrated clear superiority over an existing adjuvanted, egg-based vaccine across all four influenza strains tested. Furthermore, it proved non-inferior to a modern recombinant vaccine for most strains, a critical benchmark in the field.

The three components work in concert:
1. MF59® Adjuvant: A proprietary ingredient that acts as an immune system amplifier. It strengthens, broadens, and lengthens the body's protective response to the vaccine.
2. Cell-Based Manufacturing: Instead of using traditional chicken eggs, the vaccine antigens are grown in cultured animal cells. This modern process avoids potential virus mutations associated with egg adaptation, resulting in a vaccine that more closely matches the circulating influenza strains targeted by the World Health Organization.
3. Higher Dose: The vaccine contains a higher concentration of haemagglutinin—the key protein that stimulates immunity—than standard-dose vaccines, further optimizing the immune response in older adults.

"Influenza vaccine innovation has historically progressed through incremental advances," noted Professor Colin Russell, Chair of the European Scientific Working Group on Influenza (ESWI). "What makes this study noteworthy is that it shows the potential benefit of bringing multiple proven approaches together in a single vaccine." He added that given the persistent burden of influenza among older adults, "these findings represent an important contribution to ongoing efforts to improve protection in this vulnerable population."

The study also yielded intriguing exploratory findings related to neuraminidase antibodies, a secondary target on the influenza virus. The vaccine prompted an enhanced response of these antibodies, which emerging research suggests may contribute to reducing disease severity and providing broader protection, a promising sign in the ongoing quest for more universally effective flu vaccines.

Reshaping Public Health and Senior Care

The strategic implications of a more effective flu vaccine for seniors are immense. Older adults account for a disproportionate share of severe influenza-related illnesses, hospitalizations, and deaths. Their age-related immune decline, or immunosenescence, makes them not only more susceptible to infection but also less likely to benefit fully from standard vaccination.

By demonstrating a robust and persistent immune response throughout the flu season, aQIVc offers a powerful new tool for public health officials. The trivalent (three-strain) version of the vaccine, marketed as AUJEMFLU®, has already gained approval from regulatory bodies in the United Kingdom and the European Union for use in adults aged 50 and older. These approvals signal strong confidence from regulators in the vaccine's safety and enhanced immunogenicity profile.

"Publication in The Lancet Infectious Diseases is a significant milestone for CSL Seqirus and reflects decades of investment in influenza vaccine innovation," said Gregg Sylvester, Chief Medical Officer at the company. "These findings provide important new evidence for healthcare professionals, policy makers and immunisation advisory groups considering future influenza vaccination strategies for older adults."

The data will now be scrutinized by National Immunisation Technical Advisory Groups (NITAGs) worldwide, which make recommendations on national vaccination programs. Evidence of superior protection could lead to preferential recommendations for aQIVc in older age groups, fundamentally altering procurement strategies and public health guidelines for flu season. The ultimate goal is a measurable reduction in the clinical and economic burden of seasonal influenza.

A Calculated Investment in a Competitive Market

The launch of aQIVc is not merely a scientific achievement; it is a key pillar of CSL Seqirus's business strategy. The company has positioned itself as a leader in differentiated influenza vaccines, and aQIVc represents its most advanced offering yet. It enters a competitive landscape for enhanced senior flu shots, which includes high-dose vaccines from competitors like Sanofi and other adjuvanted options.

However, CSL Seqirus is betting that the "all-in-one" combination of three proven technologies will be a compelling differentiator for clinicians and policymakers. The company's deep investment in manufacturing is critical to this strategy. Its state-of-the-art, large-scale cell-based manufacturing facility in Holly Springs, North Carolina—built in partnership with the U.S. government—provides the capacity to produce this advanced vaccine reliably and at scale. This cell-based platform not only supports seasonal vaccine production but also positions the company as a key partner in global pandemic preparedness.

Cost-effectiveness will also play a crucial role in market adoption. While premium pricing for enhanced vaccines is common, health systems are increasingly focused on value. Early economic modeling from other markets has suggested that adjuvanted vaccines can be cost-saving compared to other enhanced options, a factor that will be critical as CSL Seqirus negotiates with payers.

With regulatory submissions underway in multiple other countries, the company is planning a phased global rollout. This strategic introduction, aligned with local regulatory and access pathways, will allow CSL Seqirus to leverage its extensive global footprint and solidify its market position as an innovator dedicated to addressing the specific needs of the world's aging population. The successful development and validation of aQIVc is a testament to the company's long-game approach, turning sustained R&D investment into a tangible asset for both public health and business growth.