According to a new study published in The Journal of Immunology, seasonal influenza vaccines induced comparable levels of antibodies, but their ability to activate cellular immunity varied significantly depending on the type of vaccine and the age of participants.
Scientists typically measure vaccine effectiveness by antibody levels, a key measure of whether the drug produces an immune response. High levels of antibodies do help protect against severe forms of influenza, but do not guarantee full immunity: the disease can reappear, although in a milder form than in unvaccinated people. To gain a better understanding of immune defenses, the researchers focused on measures of cellular immunity, which they believe better predict the strength and duration of the immune response than antibody measurements alone.
The study analyzed four vaccines: Fluzone High-Dose, Fluzone Standard-Dose, Flucelvax and Fluad. Among older participants (65-85 years), the most robust and consistent immune response from B and T cells was observed following Fluzone High-Dose vaccination. This vaccine stimulated early activation of circulating follicular helper T cells and antibody-producing cells, which promotes the formation of long-term immune memory.
In younger adults (28-60 years), Flucelvax, a mammalian cell vaccine, performed better than the egg-based Fluzone Standard-Dose vaccine. Flucelvax was more effective in activating multifunctional cytokine-secreting CD4+ T cells and inducing a stronger response from memory B cells, which are responsible for the body’s long-term defense. Scientists are now working to create a universal flu vaccine that can provide broad and long-lasting protection against all or most strains of the virus. Such a vaccine could eliminate the need for annual vaccinations.