SARS-CoV-2 serotyping based on spike antigenicity and its implications for host immune evasion.

Background: As SARS-CoV-2 continues to spread and evolve, new variants/sub-variants emerge, raising concerns about vaccine-induced immune escape. Here, we conducted a systematic analysis of the serology and immunogenicity of major circulating variants/sub-variants of SARS-CoV-2 since the outbreak.

Methods: We expressed and purified trimeric S proteins from 21 SARS-CoV-2 variants, with SARS-CoV included as an outgroup. Mice were immunized, and the resulting antisera were tested for binding antibodies after the third dose injection, and for neutralizing antibodies (NAbs) after both the second and third doses. Using pseudovirus neutralization assays, we evaluated cross-neutralization among major circulating variants. By integrating serological classification, antigenic mapping, and 3D landscape analysis, we explored the antigenic relationships among different SARS-CoV-2 variants and their impact on serological responses.

Findings: Based on the cross-neutralization activities of the sera from different S protein vaccinations and antigenicity analyses, we grouped the 21 lineages into six serotypes. Particularly, BA.2.86 and JN.1 had very weak cross-neutralization with all other SARS-CoV-2 sub-variants tested and were grouped into a separate serotype, Serotype VI.

Interpretation: This systematic study contributes to a better understanding of the evolution of SARS-CoV-2 and its antigenic characteristics and provides valuable insights for vaccine development.

Funding: This study was supported by the National Key R&D Program of China (2023YFC2307801, 2020YFA0509202 and 2021YFA1300803), the National Natural Science Foundation of China (82222040 and 82072289), CAS Project for Young Scientists in Basic Research (YSBR-083) and Beijing Nova Program of Science and Technology (20220484181).