SARS-CoV-2 (severe acute respiratory syndrome coronavirus type 2) is a new beta coronavirus identified in early 2020 as the causative agent of COVID-19. Beta coronaviruses also include SARS-CoV, MERS-CoV (Middle East respiratory syndrome coronavirus), and HKU1 and OC43 human coronaviruses (HCoV) circulating as "cold viruses."
Coronaviruses are widely distributed among mammals and birds. They cause primarily mild colds in humans, but can sometimes cause severe pneumonia. SARS-CoV-2 uses the enzyme ACE-2 as a receptor to enter host cells. A high density of ACE-2 exists in the respiratory tract, as well as in the intestine, vascular cells, kidney, heart muscle, and other organs.
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SARS CoV-2 virus variants of concern (VOC)
The SARS-CoV-2 coronavirus is changing and variants are emerging - as is the case with some other viruses.
When viruses enter body cells, they multiply there. In the process, the original virus is copied many times. When the numerous duplicates are created, small copying errors repeatedly occur in the genetic information of the virus (genome), so-called mutations. The virus accidentally created by such an "error" is called a virus variant - it is a similar, but just not identical variant of the original virus. Most of these variants have little or no impact on the pandemic, but some have important new properties. For example, they may be more contagious. In this case, virus variants can then spread more easily and quickly - and even displace the original variant in the long term.
The novel coronavirus (SARS-CoV-2), which causes the infectious disease Covid-19, changes continuously by mutations in its genome (alteration of the genetic material). These mutations can be used to determine and classify virus variants. Most mutations have little or no effect on the characteristics of the virus. However, some SARS-CoV-2 variants are characterized by altered pathogen properties that may affect the epidemiological situation, for example, by being more contagious, causing a more severe course of disease, or evading the immune response despite having undergone infection or vaccination (immune evasion).
Since the onset of the pandemic, several SARS-CoV-2 variants have been observed both globally and in the United States, including variants of concern (VOCs) alpha (B.1.1.7), beta (B.1.351), gamma (P.1), delta (B.1.617.2), and, since late November 2021, omicron (B.1.1.529 and sublines). VOCs differ relevantly from the original SARS CoV-2 virus from Wuhan (index virus) in their pathogen characteristics, such as transmissibility, virulence, or susceptibility to the immune response of recovered or vaccinated individuals.
In addition, other virus lines are under special scrutiny due to various mutations of concern associated, for example, with increased transmissibility, virulence and/or altered immune response, so-called VOI - variants of interest. WHO provides an overview of currently and previously circulating SARS-CoV-2 variants. Molecular biology details of the variants are available at SARS-CoV-2: Basic Virological Data and Viral Variants. Information on international distribution is provided at cov-lineages.org.