Nearly two years since the start of the SARS-CoV-2 pandemic, which has caused over 5 million deaths, the world continues to be on high COVID-19 alert. The World Health Organization (WHO), in collaboration with national authorities, public health institutions and scientists have been closely monitoring and assessing the evolution of SARS-CoV-2 since January 2020. The emergences of specific SARS-CoV-2 variants were characterized as Variant of Interest (VOI) and Variant of Concern (VOC), to prioritize global monitoring and research, and to inform the ongoing global response to the COVID-19 pandemic. The WHO and its international sequencing networks continuously monitor SARS-CoV-2 mutations and inform countries about any changes that may be needed to respond to the variant, and prevent its spread where feasible. Multiple variants of the virus have emerged and become dominant in many countries since January 2021, with the Alpha, Beta, Gamma, Delta and Omicron variants being the most prominent to date. The paper was aimed to review the SARS-CoV-2 variants of concern (VOC).