The SARS-CoV-2 variant classification scheme

The virus that causes covid-19 is officially called SARS-CoV-2. This website gives the definition of the various elements of this virus.

Viruses like SARS-CoV-2 continuously evolve as changes in the genetic code (genetic mutations) occur during replication of the genome. A lineage is a genetically closely related group of virus variants derived from a common ancestor. A variant has one or more mutations that differentiate it from other  variants of the SARS-CoV-2 viruses. As expected, multiple variants of SARS-CoV-2 have been documented in the United States and globally throughout this pandemic. To inform local outbreak investigations and understand national trends, scientists compare genetic differences between viruses to identify variants and how they are related to each other.

Key Definitions:

  • Mutation: A mutation refers to a single change in a virus’s genome (genetic code). Mutations happen frequently, but only sometimes change the characteristics of the virus.
  • Lineage: A lineage is a group of closely related viruses with a common ancestor. SARS-CoV-2 has many lineages; all cause COVID-19.
  • Variant: A variant is a viral genome (genetic code) that may contain one or more mutations. In some cases, a group of variants with similar genetic changes, such as a lineage or group of lineages, may be designated by public health organizations as a Variant of Concern (VOC) or a Variant of Interest (VOI) due to shared attributes and characteristics that may require public health action.

When the Omicron was labeled as a ‘variant of concern’, that label is one of four that is used to classify the nature of the danger the variant poses, which are in increasing order: Variant Being Monitored (VBM), Variant of Interest (VOI), Variant of Concern (VOC), and Variant of High Consequence (VOHC), the last being the most alarming. Delta and Omicron are the only two in the VOC category, while there are ten in the VBM category, including the Alpha and other variants with Greek letter labels that did not get much publicity.

There are none as yet that fall into the VOI nor (thankfully) the VOHC categories. One shudders to think what a VOHC variant would do.


  1. invivoMark says

    Alpha did get a fair amount of publicity. At the time it was referred to as the “UK variant” (or, in some publications, “B.1.1.7”). Similarly, Beta was called the “South African variant” and Gamma the “Brazil variant.”

    And that’s why the WHO nomenclature panel uses Greek letters -- far better to have a single, consistent, and simple way of talking about the variants that does not run the risk of inciting racist backlash. It took until Delta for everyone to start using the WHO system, for whatever reason.

  2. Jazzlet says

    Also to make it explicit variants move up the scale as data about their results come in, so both delta and omicron were previously VOIs, they and the existing VOIs were all at one point VBMs.

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