New flu vaccine trial: what the recombinant difference means this winter

What just happened

Researchers at the Doherty Institute and Singapore’s National Centre for Infectious Diseases published results from a head-to-head clinical trial comparing three types of quadrivalent flu vaccine: the traditional egg-grown formulation, a cell-grown version, and a recombinant version.

The trial enrolled 366 healthy adults aged 21 to 49 across Melbourne and Singapore. The headline result: the recombinant vaccine produced antibody levels against A(H3N2) — the flu strain most associated with severe illness and hospitalisation — that were nearly three times higher than either of the other two formulations. Safety profiles were comparable across all three, with no major concerns noted.

But the most clinically striking finding was not the headline number. It was what happened when researchers looked at vaccination history. People who had received frequent annual flu shots over multiple prior years showed a significantly blunted antibody response to the egg-grown and cell-grown vaccines — a phenomenon researchers have been trying to understand for several years. The recombinant vaccine did not produce this effect.

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The both-and

The recombinant signal is real — and the caveats are also real

The recombinant vaccine’s performance advantage is mechanistically plausible. Egg-based flu vaccine production — the dominant global manufacturing method — requires growing the virus in chicken eggs before inactivating it. During this process, the A(H3N2) strain undergoes genetic changes to adapt to the egg environment. These changes alter the surface proteins of the virus, meaning the antibodies the body produces after vaccination are calibrated to a slightly different version of H3N2 than the one circulating in the community. The recombinant approach manufactures flu proteins directly in the laboratory, skipping the egg-replication step and the associated protein drift.

This is why recombinant flu vaccines have attracted research interest — the manufacturing fidelity argument is sound. A higher-fidelity antigen presentation should produce a more precisely targeted immune response, particularly against H3N2.

The limits of this study are also worth naming clearly. Antibody levels at two weeks post-vaccination are a reasonable proxy for immune response — but they are not the same as demonstrating better real-world protection against influenza infection or reduced severity of illness over a whole flu season. The researchers note this explicitly: further studies are needed to determine whether the enhanced immune response translates into improved protection at the population level. Immunogenicity data is a promising signal; effectiveness data is the confirmation.

The repeated-vaccination blunting finding adds an important dimension. There is an emerging body of evidence that frequent annual vaccination with traditional flu vaccines can, in some people, produce a kind of immune memory imprinting that reduces response variability in subsequent years — an effect sometimes called “original antigenic sin” or immune imprinting. This is a complex and not fully resolved area of immunology. The fact that the recombinant vaccine appeared to sidestep this response pattern in this trial is interesting and worth further research. It is not yet grounds for changing vaccination strategy at a population level.

The message researchers sent — and why it matters

Both the Doherty Institute article and the researchers’ own comments are careful to say the same thing: the best flu vaccine is the one you can access. This is not a throwaway caveat. It is the most clinically important sentence in the story.

Recombinant flu vaccines are available in Australia, but not universally. Their higher manufacturing cost means they are priced above the standard formulation in private pharmacies, and they may not always be in stock at every clinic. If waiting for the recombinant option means not getting vaccinated at all before peak winter circulation — which in Australia typically runs June through September — that tradeoff is almost certainly not worth making.

The egg-grown and cell-grown flu vaccines available on the Australian Immunisation Schedule and through pharmacies this winter are not inferior products. They are the formulations with the most evidence base, the broadest availability, and decades of safety data. For most people, they are the right choice simply because they are accessible.

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My two cents

If you have not had your flu vaccine yet this winter, get it this week. Any formulation. Any approved brand. Winter 2026 is underway, and the protection window matters as much as the antibody level.

If you are a reliable annual flu vaccine recipient — someone who gets vaccinated every year without fail — it is worth asking your GP or pharmacist whether the recombinant formulation is available where you are. You are exactly the subgroup in whom the repeated-exposure immune response question is most relevant. If it is available and the cost difference is manageable, it is a reasonable choice. If it is not available or not accessible, do not wait.

And for people who have been vaccine-hesitant about flu vaccination because of year-to-year questions about how well it works: the honest answer is that flu vaccine effectiveness does vary by season, by strain match, and by individual factors including prior vaccination history. This trial adds nuance to that picture — it does not overturn the case for annual flu vaccination, which is supported by solid population-level evidence on hospitalisation prevention and mortality reduction in high-risk groups.

Getting vaccinated, this winter, with whatever is available: that is still the right call.

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Verdict: yes — worth knowing about.

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Sources cited

1. “Recombinant flu vaccine shows stronger immune response in clinical trial” — Doherty Institute, 23 June 2026. https://www.doherty.edu.au/articles/recombinant-flu-vaccine-shows-stronger-immune-response-in-clinical-trial/