Integrated analysis of humoral and memory B-cell responses reveals distinct immune landscapes shaped by influenza vaccine platforms.

Influenza vaccination is central to reducing morbidity and mortality. However, vaccine-induced immune responses vary considerably across vaccine platforms. Hemagglutination inhibition (HAI) titers are widely used as correlates of protection, but do not fully capture the complexity of memory B-cell (MBC) responses. This study employed an integrated analysis of humoral and MBC responses elicited by three licensed influenza vaccines: inactivated Fluzone standard dose (FluZ), recombinant protein-based FluBlok (FluB), and live-attenuated intranasal FluMist (FluM). FluB-vaccinees had the most robust HAI and MBC responses, with increased frequencies of switched memory and IgG memory across all HA components (H1, H3, and IBV), along with increased IgA resting memory and IgG activated memory to H1 and H3, and IgG resting memory to H1 and IBV. FluZ-vaccinees had robust, but comparatively lower responses, including increased IgG memory to H1 and IBV, but reduced switched memory compared to FluB-vaccinees. FluM-vaccinees had the lowest HAI titers but increased unswitched memory and IgA memory to H1 and IBV, along with higher IgM memory to H3. Notably, FluM-vaccinees showed greater inter-correlation among multiple MBC subsets, particularly for H3. These findings uncover distinct platform-specific immune landscape and demonstrate that FluB induces superior MBC responses, providing a framework for designing next-generation vaccines.