Abstract
SARS-CoV-2 continues to pose a global health challenge due to its high transmissibility and mutability, with new variants emerging that potentially undermine vaccination and therapeutic efforts. Mutations in the spike protein, particularly in the receptor-binding domain (RBD), significantly influence viral transmissibility and immune escape. However, the complex interplay of these mutations and their combined effects on viral fitness remain to be analyzed. In this study, we investigated the functional impact of key mutations found in the Delta and Kappa variants of SARS-CoV-2. Using pseudovirus assays, we demonstrated that the T478K and L452R mutations characteristic of the Delta variant primarily enhance viral infectivity, with minimal effect on antibody-mediated neutralization. Conversely, the E484Q mutation of the Kappa variant, alone or in combination with L452R, significantly improved evasion of antibody-mediated neutralization but appeared to compromise viral fitness and infectivity. Notably, contrary to previous reports, we found that the P681R mutation contributed neither to increased infectivity nor immune evasion at least in the assay system employed in this study. Our findings suggest that the Delta variant's global dominance over the Kappa variant may be attributed to its superior infectivity and transmissibility rather than enhanced immune evasion capabilities. These results provide valuable insights into the functional consequences of spike protein mutations and may aid in predicting the emergence and spread of future SARS-CoV-2 variants. Such understanding is crucial for enhancing public health preparedness and informing the development of next-generation vaccines and therapeutics.