The emergence and outbreak of the deadly novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in December 2019, become a global health problem in the last two years. SARS-CoV-2 is an enveloped virus with a non-segmented single-strand positive-sense RNA. It has some similarities with other coronaviruses, especially the SARS-CoV. However, the specific features of this virus have changed its pathogenicity and transmissibility compared to other coronaviruses. The distinctive structural differences of the SARS-CoV-2 spike protein have a key role in the kinetics of viral load and a broad range of virus tissue tropism. Because of these differences, SARS-CoV2 has a greater affinity for binding host cell receptor angiotensin-converting enzyme 2 than SARS-CoV. Since its emergence, the SARS-CoV-2 genome has undergone several mutations. However, a small number can alter the virus antigenicity and clinical features of the disease, leading to the formation of different SARS-CoV-2 variants. Some of these variants have higher transmissibility, severity, and impact on host immunity than the original SARS-CoV-2. Although there are currently no specific therapeutic interventions for coronavirus disease 2019 (COVID-19), manufacturers are working to make and update vaccines by continuously monitoring antigenic and genetic changes in the SARS-CoV-2 population worldwide. Some of these vaccines are very effective against different variants of the virus, therefore in some countries, with widespread vaccination and compliance with health protocols, people have largely returned to normal living conditions. To better understand SARS-CoV-2, in this article, we reviewed its classification, genome organization, structure, and life cycle. In addition, an overview of the mutations occurring in the spike protein and the characteristics of the different variants is given here. Finally, vaccines produced against this coronavirus were briefly introduced.
