Comparative immunogenicity of several inactivated influenza vaccines among healthcare workers in Hong Kong
A study of healthcare workers in Hong Kong during the 2025/26 season found that three licensed egg-based inactivated influenza vaccines (TetrAnflu, Fluarix Tetra, and Vaxigrip) demonstrated comparable immunogenicity, supporting their interchangeability in seasonal vaccination programs.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Every year, as the weather turns, health officials around the world recommend that people, especially those who work in hospitals and clinics, get a flu shot. This advice is based on a simple but vital idea: the virus that causes influenza changes its appearance slightly every season, so the protection offered by last year's shot may not be enough for this year's version. To stay safe, scientists update the recipe for the vaccine to match the specific strains of the virus expected to circulate. In many places, these vaccines are made by growing the virus in eggs, a method that has been used for decades. Because several different companies manufacture these egg-based vaccines, health departments often have to choose which brand to buy in bulk. A natural question arises: do these different brands work equally well, or does one trigger a stronger defense in the human body than the others?
In a recent study conducted in Hong Kong, researchers set out to answer this question by comparing three specific flu vaccines available in the region. They focused on healthcare workers, a group that is particularly important to protect because they are at high risk of catching the virus at work and could accidentally pass it on to vulnerable patients. The team looked at three licensed vaccines: one made by Sinovac, one by GlaxoSmithKline, and one by Sanofi. While two of these vaccines protect against four different virus strains and one protects against three, they all share a common core of ingredients designed to fight the most likely threats for the 2025 and 2026 flu season. The researchers wanted to see if the human immune system responded differently to these different brands.
To find the answer, the scientists followed a large group of healthcare workers over several years. They had access to blood samples taken from these workers before they received their flu shots and again about a month after vaccination. This timing is crucial because it allows researchers to measure exactly how much the body's defenses had risen in response to the shot. The team selected a specific group of workers who had received one of the three vaccines and carefully matched them by age and sex to ensure a fair comparison. They then tested the blood samples in a laboratory to measure the level of antibodies, which are the proteins the immune system produces to fight off infection. The test they used, known as a hemagglutination inhibition assay, is a standard way to see if the antibodies are strong enough to stop the virus from attaching to cells.
The results showed a reassuring picture. The researchers found that the three vaccines produced very similar results. The workers who received the Sinovac vaccine saw their antibody levels rise just as much as those who received the vaccines from GlaxoSmithKline or Sanofi. The number of people who developed a strong immune response was nearly the same across all three groups. Even when the scientists adjusted their analysis to account for small differences in age or the exact timing of the blood draws, the conclusion remained the same: the vaccines were interchangeable in terms of how well they stimulated the immune system.
This study provides real-world evidence that supports the idea that health officials can choose between these different brands without worrying that one is significantly weaker than the others. While the study had some limitations, such as a relatively small number of participants for each group and the fact that the workers were not randomly assigned to a specific brand, the findings align with previous large-scale trials. The research suggests that for healthy adults working in healthcare, any of these three egg-based vaccines will likely provide comparable protection. This knowledge helps public health planners make decisions based on availability and logistics rather than concerns about effectiveness, ensuring that those on the front lines of healthcare remain protected against the changing flu virus.
Drowning in papers in your field?
Get daily digests of the most novel papers matching your research keywords — with technical summaries, in your language.