Annual influenza vaccination:
Insights from longitudinal seroprotection studies

Reference: Trieu MC, Bansal A, Svik M, Ljostveit S, Jul-Larsen Á, Cox RJ. Effects of repeated influenza vaccination and infection on durable seroprotection in healthcare workers. npj Vaccines. 2025;10:213. doi:10.1038/s41541-025-01259-x.  The study investigated the effect of repeated influenza vaccination and natural infection on the development and durability of seroprotective antibody responses in Norwegian healthcare workers (HCWs) over four influenza seasons following the 2009 H1N1 pandemic vaccination. It addresses the ongoing debate about whether repeated annual vaccination might blunt antibody responses—particularly in high-risk groups such as HCWs—while aiming to clarify optimal strategies for long-term protection.  Study Design Researchers followed 250 HCWs, all of whom first received the AS03-adjuvanted monovalent H1N1pdm09 vaccine in 2009. Over the next four influenza seasons (2010–2014), many voluntarily received annual trivalent inactivated vaccines (TIVs) containing the same H1N1pdm09 component, but variable A(H3N2) and B strains. Both vaccinated and unvaccinated participants were followed, with serial blood sampling and serological testing to measure...