The article reviews the evolution of SARS-CoV-2 Omicron variants, focusing on their genetic impact on viral fitness. It discusses the molecular characteristics of SARS-CoV-2, including its genome structure, key proteins, and their roles in viral replication and immune evasion. The evolution of SARS-CoV-2 variants is analyzed, highlighting the emergence of Omicron and its sublineages, such as BA.1, BA.2, BA.4, BA.5, BQ.1, BQ.1.1, XBB, and BA.2.86. These variants have undergone numerous mutations, leading to increased transmissibility, immune evasion, and changes in viral fitness. The article also explores the origins of Omicron, proposing several hypotheses, including prolonged viral replication in immunocompromised individuals, mutations in non-human hosts, and under-sampled regions. The impact of mutations in Omicron on viral fitness is discussed, emphasizing immune evasion, cell infectivity, and cross-species transmission. Mutations in the S protein, particularly in the receptor-binding domain (RBD), have been shown to enhance immune evasion and binding affinity to ACE2. The article also highlights the role of accessory proteins and non-structural proteins in viral evolution and their impact on immune evasion and pathogenesis. Finally, the cross-species transmission potential of SARS-CoV-2 is discussed, noting its ability to infect various animal species, which may contribute to viral evolution and the emergence of new variants. The study provides insights into the genetic and biological factors driving the evolution of SARS-CoV-2 variants and their implications for public health and vaccine development.The article reviews the evolution of SARS-CoV-2 Omicron variants, focusing on their genetic impact on viral fitness. It discusses the molecular characteristics of SARS-CoV-2, including its genome structure, key proteins, and their roles in viral replication and immune evasion. The evolution of SARS-CoV-2 variants is analyzed, highlighting the emergence of Omicron and its sublineages, such as BA.1, BA.2, BA.4, BA.5, BQ.1, BQ.1.1, XBB, and BA.2.86. These variants have undergone numerous mutations, leading to increased transmissibility, immune evasion, and changes in viral fitness. The article also explores the origins of Omicron, proposing several hypotheses, including prolonged viral replication in immunocompromised individuals, mutations in non-human hosts, and under-sampled regions. The impact of mutations in Omicron on viral fitness is discussed, emphasizing immune evasion, cell infectivity, and cross-species transmission. Mutations in the S protein, particularly in the receptor-binding domain (RBD), have been shown to enhance immune evasion and binding affinity to ACE2. The article also highlights the role of accessory proteins and non-structural proteins in viral evolution and their impact on immune evasion and pathogenesis. Finally, the cross-species transmission potential of SARS-CoV-2 is discussed, noting its ability to infect various animal species, which may contribute to viral evolution and the emergence of new variants. The study provides insights into the genetic and biological factors driving the evolution of SARS-CoV-2 variants and their implications for public health and vaccine development.