Abstract
<jats:p>Vaccine immunogenicity declines with age due to immunosenescence, underscoring the need for improved adjuvants. LiteVax Adjuvant (LVA), a squalane-in-water emulsion containing carbohydrate fatty-acid monosulphate esters, has shown potential to enhance influenza vaccine responses, but its mechanisms in humans remain unclear. We performed a longitudinal systems vaccinology study in 56 younger (18-45 years) and older (≥60 years) adults receiving a quadrivalent influenza vaccine with or without LVA. Multi-omics analyses, including bulk and single-cell transcriptomics, flow cytometry, and serology, revealed that LVA induced a rapid, transient interferon-driven innate response, primarily in monocytes, associated with enhanced antigen processing and dendritic cell to T cell interactions. LVA promoted differentiation of influenza-specific CD4⁺ T cells toward CD45RO+ memory phenotypes, accelerated early IgG3 antibody responses, and increased IgG-producing plasmablast frequencies without affecting overall antibody magnitude. Importantly, LVA reduced age-related differences in early immune responses, improving response quality and supporting vaccine performance in older adults.</jats:p>