Classification of five SARS-CoV-2 serotypes based on RBD antigenicities

Here is a detailed summary for the study titled “Classification of five SARS-CoV-2 serotypes based on RBD antigenicities”:


  • Context: The COVID-19 pandemic, caused by SARS-CoV-2, has led to the emergence of numerous variants, particularly Omicron and its sub-variants. These variants have shown increased immune escape, leading to reduced effectiveness of existing vaccines and antibodies.
  • Objective: Given the diminished cross-neutralization among these variants, the study aimed to classify SARS-CoV-2 into multiple serotypes based on the antigenicities of their receptor-binding domains (RBDs).


  • Approach: The study selected 23 representative SARS-CoV-2 variants, including pre-Omicron and Omicron sub-variants. They used mRNA vaccines derived from these variants’ RBDs and vaccinated mice to evaluate cross-neutralization.
  • Data Analysis: The antisera from the vaccinated mice were used to systematically assess the neutralization of pseudotyped viruses of the 23 variants, leading to the classification of the variants into five distinct serotypes based on their RBD antigenicities.

Key Findings

  1. Serotype Classification:
    • Serotype-I: Includes all pre-Omicron variants, further classified into two subtypes (Ia and Ib).
    • Serotype-II: Comprises BA.1 and BA.1.1 sub-variants.
    • Serotype-III: Includes variants like BA.3, BA.2, BA.12.1, and BA.2.75.
    • Serotype-IV: Encompasses variants like BA.5, BF.7, BQ.1, and BQ.1.1.
    • Serotype-V: Contains XBB and XBB.1.5 variants.
  2. Implications for Vaccine Development:
    • The study suggests that including reference members from serotypes Ib, IV, and V could lead to broad protection against all SARS-CoV-2 variants.
    • Vaccines based on XBB and its derivatives have shown effective immune responses against current circulating variants, emphasizing the need for their development and distribution.


  • Comparison with Other Viruses: The classification of serotypes is instrumental in the prevention and control of various viruses, like human papillomavirus (HPV) and dengue virus (DENV), and is crucial for vaccine development.
  • SARS-CoV-2 Serotype Divergence: The emergence of Omicron and its sub-variants has led to a significant decrease in cross-neutralization with previous variants, supporting the discussion of classifying Omicron as a new serotype.
  • Challenges and Future Directions: The classification was based on antisera cross-neutralization using RBD-based mRNA vaccines to simulate infection. Further research is needed to consider the entire antigenic spectrum of SARS-CoV-2 for comprehensive serotype classification.


The study proposes classifying SARS-CoV-2 variants into five serotypes based on RBD antigenicities, which could guide the rapid assessment of future variants and aid in the development of broad-spectrum COVID-19 vaccines and neutralizing antibodies​​.

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