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A virus always mutates. It is the same with the COVID-19 virus. Today, we see a number of SARS-CoV-2 variants that have emerged from immunocompromised hosts. According to researchers from the Microbiology Society, variants of concern, including B.1.1.7, a variant first identified in Kent, were a result of long-term infection in people with a weakened immune system. They are of the opinion that persistent infections in immunocompromised people may cause the virus to mutate more frequently. This happens because the immune system of such people cannot clear the virus as quickly as the immune system of a healthy person. In such a scenario, monitoring genetic changes in the COVID-19 virus is the only way that will help scientists control the virus in future.
Researchers who conducted this study say that as more and more COVID-19 variants appear, they are getting a better picture of their shared similarities and differences. This helps them predict what other new variants will look like in a more informed manner. Putting all this information together will also help them design booster vaccines that can offer protection against as many variants as possible or design targeted diagnostics.
The review of the researchers discusses where mutations have occurred, what part of the virus they affect and how the resulting variants could impact vaccination efforts. According to the authors of this review, mutations are expected because the virus is adapting to humans. Till now, the sequencing of other seasonal coronaviruses has not been done. But SARS-CoV-2 is at the start of its journey in humans. Variants with the same or similar mutations have emerged independently in different countries. This virus is still finding its way in humans as far as optimal infection and transmission is concerned. Researchers are hopeful that massive sequencing efforts will identify concurrent mutations.
Mutations of particular interest include those in the spike protein. This protein allows the virus to enter host cells and is the main target of the immune system, including immunity generated by all current SARS-CoV-2 vaccines. Mutations in the gene that codes for spike could change the shape of the protein, allowing it to no longer be recognised by the immune system. Because this protein is so important for entry of the virus, favourable mutations are more likely to succeed and create new, dominant variants of the virus.
Changes that give the virus an advantage can quickly become dominant. For example, one mutation, named D614G, was found in 80 per cent of COVID-19 viruses sequenced just four months after it was first detected. Now, viruses without the D614G mutation are only commonly seen in parts of Africa. Another mutation, N501Y, is found in the variant B.1.1.7. This mutation is believed to be the result of infection of an immunocompromised individual and may contribute to the virus being more contagious and deadly. The B.1.1.7 UK variant became the dominant variant within three months and is now responsible for over 90 per cent of infections there.
Researchers reviewed a number of spike protein mutations. We list them here.
As early as in February 2020, a mutation was detected in the spike protein of SARS-CoV-2 and named D614G. This mutation makes COVID-19 more infectious but not more harmful. This led to a major viral fitness advantage and within four months, 80 per cent of COVID-19 viruses sequenced around the world carried the mutation. At present, only parts of Africa have circulating viruses without this particular mutation. Initially there were concerns that this variant will be immune to vaccines. But now, experts say that D614G does not have an effect on vaccine efficiency. In fact, in some cases, viruses with this mutation are more readily cleared by antibodies against COVID-19.
In mid-2020, many reports of mink becoming infected by humans started doing the rounds. In mink, the spike protein of the virus commonly developed two mutations called Y435F and N501T. These mutations allow for stronger binding of the virus to human receptor cells. These COVID-19 variants were found in Denmark and it was believed to have originated from mink. This variant came to the limelight as it was able to infect people who had previously been infected and were thought to have acquired antibodies against the virus. This mutation develops in an immunocompromised person, possibly as a result of chronic infection with the virus allowing it to adapt.
Towards the end of 2020, in December 2020 to be specific, another highly contagious variant of COVID-19 was isolated in Kent, UK. This variant, named B.1.1.7, contained a mutation in the spike protein called N501Y which make the virus more contagious and deadly. It is now the dominant variant in the UK and is responsible for over 90 per cent of infections there. It has little effect on immunity from both vaccines and previous infections.
The most recent spike protein mutation is E484K. It emerged in once in South Africa and at least twice in Brazil. Variants with this mutation are able to evade the immune system of both vaccinated and previously infected individuals. Scientists think that this mutation was driven by high levels of population immunity, which drove mutations in the spike protein to evade the immune system.
(With inputs from Agencies)
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