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Seasonal flu vaccination increases susceptibility to other flu strains in the future
Last reviewed: 01.07.2025
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Annual influenza vaccination of children leads to the development of cross-reactive T cells to influenza viruses, according to a paper in the November issue of the Journal of Virology.
Cross-resistance is the development of resistance to an agent that leads to resistance to a similar agent.
In this study, author Rogier Bodewes of Erasmus Medical Center in the Netherlands and colleagues collected blood samples from children with cystic fibrosis who were vaccinated against influenza annually and from healthy controls who were not vaccinated. The blood samples were tested for the presence of virus-specific killer T cells.
Most virus-specific killer T cells are directed to attack constant viral proteins that are found among different influenza viruses, as opposed to the rapidly changing, non-constant proteins that are the targets of antibodies induced by influenza vaccines.
The scientists found that the number of virus-specific T cells increased with age in unvaccinated children, while no such increase was seen in children vaccinated every year. "In fact, vaccination appeared to interfere with the induction of virus-specific killer T cells," says the study's author. "Vaccinated children [with CF] will develop a less pronounced cross-reactive virus-specific CD8+ T cell response than unvaccinated children."
"Most countries recommend annual influenza vaccination for certain high-risk groups," says Rogier Baudiues. "In addition, some countries recommend annual influenza vaccination for all healthy children starting at six months of age."
This study shows potentially contradictory implications for vaccine policy. Annual influenza vaccination is effective against seasonal influenza, but may make people more vulnerable to future influenza pandemic viruses, as the induction of virus-specific killer T cells by childhood influenza infection may reduce resistance to future pandemic influenza viruses.
Referring to the report, the expert says the findings "support the need for the development and use of universal influenza vaccines for children, particularly in light of the threat of avian influenza A/H5N1 pandemic." However, efforts to develop such a vaccine have been stymied for decades by the complexity of the internal orientation of influenza virus proteins.