Epidemiology and Characteristics of SARS-CoV-2 Variants of Concern: The Impacts of the Spike Mutations

SARS-CoV-2 expresses on its surface the Spike protein responsible for binding with the ACE2 receptor and which carries the majority of immunodominant epitopes. Mutations mainly affect this protein and can modify characteristics of the virus, giving each variant a unique profile concerning its transmissibility, virulence, and immune escape. The first lineage selected is the B.1 lineage characterized by the D614G substitution and from which all SARS-CoV-2 variants of concern have emerged. The first three variants of concern Alpha, Beta, and Gamma spread in early 2021: all shared the N501Y substitution. These variants were replaced by the Delta variant in summer 2021, carrying unique mutations like the L452R substitution and associated with higher virulence. It was in turn quickly replaced by the Omicron variant at the end of 2021, which has predominated since then, characterized by its large number of mutations. The successive appearance of variants of concern showed a dynamic evolution of SARS-CoV-2 through the selection and accumulation of mutations. This has not only allowed progressive improvement of the transmissibility of SARS-CoV-2, but has also participated in a better immune escape of the virus. This review brings together acquired knowledge about SARS-CoV-2 variants of concern and the impacts of the Spike mutations.