SARS-CoV-2 variants occur when there are changes or “mutations” in the original virus’ genetic code. These changes occur naturally over time as a by-product of replication. The World Health Organization (WHO) tracks variants of SARS-CoV-2 around the globe and designates them as variants of concern (VOCs) when they meet specific criteria demonstrating that they spread much faster, are better adept at infecting people and/or impact the effectiveness of vaccines and therapeutics.
Currently there are five VOCs: Alpha, Beta, Gamma, Delta, and Omicron. The Alpha variant, also known as the B.1.1.7 variant, was first identified in the United Kingdom where a mutation occurred in the receptor binding domain (RBD) of the spike protein. This resulted in a change of the genetic code, specifically, the amino acid asparagine (N) was replaced with tyrosine (Y) at location 501 (N501Y).
The Beta variant, also known as B.1.351 originated in South Africa, the Gamma variant, also known as P.1, originated in Brazil, the Delta variant, also known as B.1.617.2, originated in India and the newest variant entitled Omicron emerged in November 2021. Beta and Gamma variants also have the above N501Y mutation, but they have several others, like E484K. The Delta variant has a more diverse repertoire of mutations than other variants. It lacks the N501 mutation, has a different mutation in position 484 (E484Q), and has several other unique mutations (including P681R and L452R). The Omicron variant has over 30 mutations in the spike protein alone.
The WHO also tracks variants of interest (VOIs), defined as variants with mutations that could affect transmissibility, disease severity, and the effectiveness of immune responses and therapeutics. Currently, there are five VOIs: Eta (B.1.525), Iota (B.1.526), Kappa (B.1.617.1), Lambda (C.37), and Mu (B.1.621).