JN.1 mRNA vaccine boosts humoral and cellular immunity against SARS-CoV-2 variants, enhancing protection.

The continuous evolution of SARS-CoV-2 raises significant concerns about immune escape from existing immunity. While the monovalent JN.1-adapted mRNA vaccine was developed to better match circulating variants, comprehensive data on its ability to induce and broaden both humoral and cellular immunity in individuals, regardless of prior infection status, has been limited. Understanding these immune responses is crucial for assessing vaccine effectiveness and informing public health strategies against emerging variants.

Researchers recruited 37 immunocompetent adults to assess vaccine-induced immunity before and two weeks after JN.1 vaccination. Spike-specific CD4 and CD8 T cells were quantified following stimulation with spike-derived peptides from the parental strain, XBB.1.5, and JN.1. Their CTLA-4 expression and cytokine profiles were analyzed by flow cytometry. Additionally, spike-specific IgG levels and neutralizing activity against authentic parental, XBB.1.5, JN.1, and KP.3.1.1 isolates were measured to provide a comprehensive picture of the immune response.

JN.1 vaccination significantly increased spike-specific CD4+ and CD8+ T-cell frequencies, demonstrating robust cellular immune activation. These T-cell responses exhibited comparable cytokine profiles across different variants (parental, XBB.1.5, JN.1) and enhanced CTLA-4 expression, suggesting a broad and potentially regulatory T-cell response. Humoral immunity also saw marked improvements: IgG levels and neutralizing titers rose significantly. > The strongest relative increases in neutralizing titers were observed against Omicron lineage variants, including JN.1 and KP.3.1.1, indicating improved protection against current circulating strains. Prior infection was associated with higher baseline neutralizing titers but notably did not influence the magnitude or breadth of vaccine-induced T-cell responses. Furthermore, co-administration with the influenza vaccine had no adverse effect on JN.1 immunogenicity, supporting concurrent vaccination strategies.