The article provides a comprehensive review of the evolution and biological implications of the Omicron variant of SARS-CoV-2, focusing on its sublineages. It highlights the genetic changes that have contributed to the variant's increased fitness, including immune evasion, enhanced cell infectivity, and cross-species transmission potential. The authors discuss the molecular biological characteristics of SARS-CoV-2, detailing its genome organization and the roles of its structural and accessory proteins. They also explore the evolutionary history of Omicron, noting that its origin remains unclear but may have involved prolonged viral replication in immunocompromised individuals or non-human hosts. The impact of mutations on viral fitness is examined, with a focus on immune evasion through changes in the receptor-binding domain (RBD) and neutralization by immune sera and monoclonal antibodies. The article further discusses the virus's ability to infect cells and tissues, including its preference for upper respiratory tract infection and the potential for non-systemic infections. Additionally, it addresses the role of mutations in other viral proteins and the potential for cross-species transmission. Finally, the authors emphasize the need for further research to develop effective prevention strategies and treatments against emerging variants.The article provides a comprehensive review of the evolution and biological implications of the Omicron variant of SARS-CoV-2, focusing on its sublineages. It highlights the genetic changes that have contributed to the variant's increased fitness, including immune evasion, enhanced cell infectivity, and cross-species transmission potential. The authors discuss the molecular biological characteristics of SARS-CoV-2, detailing its genome organization and the roles of its structural and accessory proteins. They also explore the evolutionary history of Omicron, noting that its origin remains unclear but may have involved prolonged viral replication in immunocompromised individuals or non-human hosts. The impact of mutations on viral fitness is examined, with a focus on immune evasion through changes in the receptor-binding domain (RBD) and neutralization by immune sera and monoclonal antibodies. The article further discusses the virus's ability to infect cells and tissues, including its preference for upper respiratory tract infection and the potential for non-systemic infections. Additionally, it addresses the role of mutations in other viral proteins and the potential for cross-species transmission. Finally, the authors emphasize the need for further research to develop effective prevention strategies and treatments against emerging variants.