SARS-CoV-2 And Its Variants

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SARS-CoV-2 is the theme of everyone’s life in the whole 2020 and still continues in 2021. A SARS-CoV-2 variant with spike protein mutations in UK by the end of 2020 renews the fear. This article will explain the variants of the virus.

Although SARS-CoV-2 is a class of RNA virus, it is relatively stable during transmission in human populations. Like all coronaviruses, SARS-CoV-2 makes fewer mutations than most RNA viruses because it encodes an enzyme responsible for correcting some of the errors that occurred during replication. Whereas, the RNA recombination of coronaviruses accounts for a relatively high rate, which leads to alterations in the RNA sequence and subsequent changes in the viral proteins. The production of a new mutation is mostly determined by natural selection. The emerged variants often are those that possess a competitive advantage in viral replication, transmission, and immune evasion.

The spike (S) protein of SARS-CoV-2 directly interacting with the host receptor and mediating viral entry into the host cells make it face the most selective pressure. So many identified mutations of SARS-CoV-2 are concentrated on the S protein. SARS-CoV-2 constantly changes through mutation, and novel variants of the SARS-CoV-2are expected to occur over time. Scientists have been dedicated to sequencing these existing SARS-CoV-2 variants to monitor the mutations of the virus and predict the evolution of the pandemic.

Currently, the SARS-CoV-2 variant with a D614G mutation in the S protein-encoding gene has dominated globally. According to the World Health Organization (WHO), the SARS-CoV-2 S protein D614G variant was found in late January and early February 2020 and gradually replaced the original strain over the following months. By June 2020, this variant becomes the dominant virus type circulating worldwide. Studies have shown that the variant is more infectious and transmissible than the original strain, but does not cause more severe disease.

From August to September 2020, a SARS-CoV-2 variant related to farmed mink was discovered in Denmark. It was named “Cluster 5”, with a mutation that had not been observed before. According to preliminary research conducted in Denmark, this variant may reduce the extent and duration of immune protection after natural infection or vaccination, and relevant evaluations are still ongoing. So far, Denmark has only found 12 cases of human infection with this variant in September, and the variant does not appear to spread widely.

Afterward, the United Kingdom reported on December 14, 2020, a variant of the SARS-CoV-2 named “VOC 202012/01” that first appeared in the southeast of England. Preliminary epidemiological studies have shown that this variant is more transmissible but based on the length of hospitalization and 28-day mortality rate, the severity of the disease and the reinfection situation have not changed. And most diagnostic tools are not affected. As of December 30, the variant has been found in 31 other countries and regions in five of the six WHO regions.

In addition, on 18 December 2020, South Africa detected a virus variant with N501Y mutation and named it the “501Y.V2” variant. This variant is rapidly spreading in three provinces in South Africa. Although the mutant virus previously discovered in the UK also has the N501Y mutation, analysis shows that it is a different variant from that found in South Africa. Preliminary studies have shown that this variant is associated with a higher viral load or increased infectivity, but there is no evidence that it can cause more serious illness. Further investigation is needed. As of December 30, the variant has been discovered in four countries outside of South Africa.

With the COVID-19 pandemic gathering momentum, an effective vaccine is the best hope for ending the pandemic and returning the world to normal. Multiple SARS-CoV-2 variants are globally circulating. Studying SARS-CoV-2 mutations is therefore an important part of vaccine development. The vaccines developed around the world most target the SARS-CoV-2 S protein. This means if the viral S protein alters, the vaccine may be less effective. Actually, preliminary studies have shown that some of the variants reported so far may increase in infectivity and transmissibility but not disease severity. No data demonstrate that they affect the effectiveness of existing diagnostics, vaccines, and other measures. Some emerging mutants may compromise the potential of drugs that support antibodies to block the virus from infecting cells. Scientists are working to learn more about these SARS-CoV-2 variants to better understand whether the authorized vaccines are still effective against viral mutants.