Lancet Study Validates Triple-Approach Flu Vaccine for Older Adults

CSL Seqirus announced this week that a large clinical trial of its experimental influenza vaccine has cleared a significant hurdle: publication in The Lancet Infectious Diseases, one of the field's most rigorous journals. The vaccine, which combines three separate technologies that have each been used in flu shots for years, represents the first time researchers have tested all three together in a single formulation at scale. The company is betting this combination will offer older adults—whose immune systems weaken with age—better protection against seasonal influenza than the shots currently available.

Influenza remains a stubborn public health problem. Despite decades of vaccination campaigns, the virus still causes substantial illness, hospitalizations, and deaths every year, particularly among people over fifty. The immune system's declining responsiveness with age means that standard vaccines often fail to generate strong enough protection in this vulnerable group. CSL Seqirus's approach stacks three proven enhancements: MF59, an adjuvant that amplifies and broadens the immune response; cell-based manufacturing, which preserves a closer genetic match to circulating strains compared to the traditional egg-based method; and a higher dose of the active ingredient—45 micrograms per strain instead of the standard amount.

The Phase 3 trial enrolled 7,699 adults aged fifty and older across eight countries: Canada, Denmark, Estonia, Germany, Pakistan, the Philippines, the United Kingdom, and the United States. Participants received one of three vaccines: the new combination shot, an MF59-adjuvanted egg-based vaccine, or a recombinant vaccine. The study measured immune response, safety, and consistency of manufacturing. The results met the researchers' primary goals. The new vaccine showed superiority over the egg-based adjuvanted comparator across all four influenza strains tested in every age group. Against the recombinant vaccine, it achieved non-inferiority for three of four strains in the fifty-plus group and all four strains in those sixty-five and older. Immune responses persisted throughout the influenza season. Side effects were mild to moderate in most cases and resolved within three days.

One finding drew particular attention from researchers: the vaccine generated enhanced antibody responses against neuraminidase, a protein on the influenza virus surface. The role of these antibodies is still being mapped, but emerging evidence suggests they may reduce disease severity and provide protection beyond what traditional vaccine measures capture. The study authors concluded that the findings warrant further evaluation and provide evidence for national immunization advisory groups considering enhanced flu vaccination strategies for older populations.

The vaccine's path to patients has already begun. The trivalent formulation—containing three instead of four influenza strains—received approval from the UK's Medicines and Healthcare products Regulatory Agency earlier this year for adults fifty and older. The European Commission has also approved it. The vaccine is marketed as AUJEMFLU. CSL Seqirus has filed regulatory submissions in multiple markets and expects a phased rollout aligned to local regulatory requirements and immunization policy decisions. Gregg Sylvester, the company's chief medical officer, called the Lancet publication a milestone reflecting decades of investment in flu vaccine innovation. Colin Russell, chair of the European Scientific Working Group on Influenza and a professor at Amsterdam University Medical Center, noted that influenza vaccine progress has historically moved in small incremental steps. What distinguishes this work, he said, is the demonstration that combining multiple proven technologies in one vaccine can yield meaningful benefits for a population that remains at high risk despite widespread vaccination.