Long-Term Durability and Variant-Specific Modulation of SARS-CoV-2 Humoral and Cellular Immunity over Two Years

There is an increasing need to understand the long-term dynamics and quality of SARS-CoV-2 immune memory-both humoral and cellular-particularly with emerging variants. This study aimed to evaluate immune durability and variant-specific modulation through a longitudinal analysis of individuals with diverse SARS-CoV-2 exposure histories, over two years after infection and/or vaccination. The study involved assessing anti-spike IgG and IgA levels over time and analyzing their relationship with neutralizing activity against both ancestral and Omicron SARS-CoV-2 variants. Persistence of T cell responses was evaluated using intracellular cytokine staining (ICS) and activation-induced marker (AIM) assays. Anti-S IgG levels remained stable over time and increased after each immune stimulation, suggesting cumulative immune memory. Neutralizing capacity correlated strongly with IgG levels, showing long-term stability for pre-Omicron variants, but a moderate decline for Omicron. CD4⁺ and CD8⁺ T cell responses persisted across all groups, largely unaffected by Omicron mutations. However, cytokine profiles revealed subtle, variant-dependent changes. These findings underscore the durability of cellular immunity and the comparatively reduced robustness of Omicron-specific humoral responses. Such insights are crucial for understanding long-term protection against evolving SARS-CoV-2 variants and guiding public health strategies.