SARS-CoV-2 Omicron variant, a variant of concern (VOC), known as B.1.1.529, was detected in South Africa at the end of November in 2021. However, it rapidly spread all over of the world and now it is the dominant variant in the world, which account for more than 90% of the new cases. Omicron variant spike protein carries around 30 amino acid changes, including mutations, deletions and insertions, in which the receptor binding domain (RBD) protein contains 15 mutations. Enhanced transmission of the Omicron variant was observed globally, which is at least 70 times more contagious than the other variants. The Omicron variant affects the effectiveness of COVID-19 vaccine and is resistant to neutralization (monoclonal antibody treatments) to a large extent.