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Sep 1, 2023 · It’s estimated that Delta caused more than twice as many infections as previous variants—in Connecticut, it was estimated to have been 80 to 90% more transmissible than the Alpha variant. In the U.S., in June 2021, after a steady decline in COVID-19 cases and hospitalizations, the arrival of Delta coincided with a rapid reversal of that trend.
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- kathy.katella-cofrancesco@yale.edu
- What You Need to Know
- Key Definitions
- Types of Classification
- Recombinants
- Summary of Variant Classifications
- List of Variants
- References
- Related Pages
•Viruses like SARS-CoV-2 continuously evolve as changes in the genetic code (caused by genetic mutations or viral recombination) occur during replication of the genome.
•SARS-CoV-2 has consistently mutated over the course of the pandemic, resulting in variants that are different from the original SARS-CoV-2 virus.
•Throughout the COVID-19 pandemic, many variants of SARS-CoV-2 have been found in the United States and globally.
•Scientists use multiple classification systems to describe and communicate similarities and differences between SARS-CoV-2 viruses.
•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.
•Sublineage: A term used to define a lineage as it relates to being a direct descendent of a parent lineage. For example, BA.2.75 is a sublineage of BA.2.
•Variant: A variant is a viral genome (genetic code) that may contain one or more mutations. In some cases, a lineage or group of lineages with similar genetic changes, may be designated by the World Health Organization (WHO) or the U.S. SARS-CoV-2 Interagency Group (SIG) as a Variant of Interest (VOI), Variant of Concern (VOC), Variant of High Consequence (VOHC) or Variant Being Monitored (VBM) due to shared attributes and characteristics that may require public health action.
There are multiple ways in which SARS-CoV-2 viruses are classified. Each classification type can be appropriate, depending on the context in which SARS-CoV-2 is being communicated. SARS-CoV-2 is often discussed in the context of lineages (and sublineages). The most commonly used classification system for lineages is Pango. Nextclade may also be use...
All coronaviruses have the potential to undergo a natural process called “recombination”. This can occur when two different lineages infect the same cell in someone at the same time. This rare phenomenon may affect the characteristics of the virus – including its ability to spread, cause severe disease or make treatments or vaccines less effective. In many cases, recombinant viruses do not have competitive advantages that help them rise.
CDC’s genomic surveillance systems can reliably detect and monitor the spread of variants, including recombinants. When a recombinant does emerge, CDC scientists evaluate and monitor the new recombinant just like any other variant lineage – including how it might be classified or when it should be presented on CDC’s COVID Data Tracker.
Variant of High Consequence (VOHC)
A VOHC has clear evidence that prevention measures or medical countermeasures (MCMs) have significantly reduced effectiveness relative to previously circulating variants. CDC monitors all variants circulating in the United States. In addition to the possible attributes of a variant of concern, variants designated as VOHC include impact on MCMs such as:
•demonstrated failure of diagnostic test targets.
•evidence to suggest a significant reduction in vaccine effectiveness, a disproportionately high number of infections in vaccinated persons, or very low vaccine-induced protection against severe disease.
•significantly reduced susceptibility to multiple EUA or approved therapeutics.
•more severe clinical disease and increased hospitalizations.
References for SARS-CoV-2 Variant Classifications and Definitions
1.Zhou, B., Thi Nhu Thao, T., Hoffmann, D. et al. SARS-CoV-2 spike D614G change enhances replication and transmission. Nature(2021). https://doi.org/10.1038/s41586-021-03361-1
2.Volz E, Hill V, McCrone J, et al. Evaluating the Effects of SARS-CoV-2 Spike Mutation D614G on Transmissibility and Pathogenicity. Cell 2021; 184(64-75). doi: https://doi.org/10.1016/j.cell.2020.11.020
3.Korber B, Fischer WM, Gnanakaran S, et al. Tracking Changes in SARS-CoV-2 Spike: Evidence that D614G Increases Infectivity of the COVID-19 Virus. Cell 2021; 182(812-7) doi: https://doi.org/10.1016/j.cell.2020.06.043
4.Yurkovetskiy L, Wang X, Pascal KE, et al. Structural and Functional Analysis of the D614G SARS-CoV-2 Spike Protein Variant. Cell 2020; 183(3): 739-751. doi: https://doi.org/10.1016/j.cell.2020.09.032
5.*Davies NG, Abbott S, Barnard RC, et al. Estimated transmissibility and impact of SARS-CoV-2 lineage B.1.1.7 in England. MedRXiv 2021. doi: https://doi.org/10.1101/2020.12.24.20248822
•New Variants of the Virus that Causes COVID-19
•Data & Surveillance
•COVID-19 Genomic Epidemiology Toolkit
Last Updated Sept. 1, 2023
Variants of severe acute respiratory syndrome coronavirus 2 ( SARS-CoV-2) are viruses that, while similar to the original, have genetic changes that are of enough significance to lead virologists to label them separately. SARS-CoV-2 is the virus that causes coronavirus disease 2019 (COVID-19).
Nov 15, 2023 · The highly transmissible COVID-19 delta variant, also known as B1617.2, was found in India in October 2020. It was the dominant strain in the U.S. and several other countries during the fall of ...
Verywell Health via YahooJN.1 COVID Variant Symptoms vs. Allergy Symptoms
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- World Health Organization
Statement on the antigen composition of COVID-19 vaccines
April 2024 statement on the antigen composition of COVID-19 vaccines
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Current variants of concern; Name Lineage Status; Omicron: B.1.1.529: Identified in southern Africa in Nov. 2021 and spread around the world. Within a month it was dominant in the U.S.
Mar 24, 2021 · Across the world, there are multiple variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (Covid-19).
Dec 31, 2020 · Since the start of the COVID-19 pandemic, WHO has received several reports of unusual public health events possibly due to variants of SARS-CoV-2. WHO routinely assesses if variants of SARS-CoV-2 result in changes in transmissibility, clinical presentation and severity, or if they impact on countermeasures, including diagnostics, therapeutics ...
