Abstract: Since the outbreak of COVID-19, SARS-CoV-2 has continued to evolve. As the fifth variants of concern (VOCs) announced by the World Health Organization, Omicron has significantly changed from previous VOCs in terms of genome, biological and epidemiological characteristics. Although the severe illness and mortality caused by Omicron infection are significantly lower than those caused by the previous VOCs, Omicron's strong transmission ability has continued to break through the epidemic prevention barrier and human immunity barrier established by prior infections and vaccines. Omicron has opened a new chapter in the COVID-19 pandemic. In this paper, we review the changes in genome and biological characteristics of Omicron and its subspecies as well as the differences in epidemiological characteristics between Omicron and influenza viruses in order to provide scientific basis for the optimization of epidemic prevention and control.