SARS-CoV-2 lineages

News Highlights:

The current surge in Covid-19 infections in China, is believed to be driven by the SARS-CoV-2 lineages that is circulating over there.

SARS-CoV-2 lineages circulating in China:

• How are variants created:
  • SARS-CoV-2, the virus that causes COVID-19, is an RNA virus which evolves by accumulating genetic errors in its genome.
  • These errors are produced when the virus infects a person and makes copies of itself inside the host’s cells.
  • These errors (otherwise called mutations) are therefore a by-product of replication of SARS-CoV-2 inside the cell and may be carried forward as the virus continues to infect people.
  • When viruses having a specific set of errors or mutations infect a number of people, this forms a cluster of infections descending from a common parental virus genome and is known as a lineage or a variant of the virus.
• Early identification of emerging variants:
  • Genome sequencing of the virus and rapid sharing of data has been key to tracking the evolution of SARS-CoV-2 and early identification of emerging variants.
  • SARS-CoV-2 sequencing data previously submitted from China to GISAID, a globally accessible repository of SARS-CoV-2 genome sequences, shows that over the months, the country has seen isolated cases linked to multiple variants of the virus seen previously. 

Omicron sublineages which are under monitoring:

• BF.7 Variant:
  • The dominant virus strain in China is BF.7, a sub-variant of Omicron that has been in circulation for over a year now.
  • There are over 500 Omicron sub-variants currently in circulation.
  • BF.7 is the name for the BA.5.2.1.7, which itself has evolved from the BA.5 sub-variant.
  • BF.7 is not unique to China.
  • It accounted for over 5% of the cases in the US in October, 2022 and over 7% of the cases in the UK.
  • When viruses mutate, they create lineages and sub-lineages— like the main trunk of the SARS-CoV-2 tree sprouting branches and sub-branches.
  • A research study reported that the BF.7 sub-variant has a 4.4-fold higher neutralisation resistance than the original D614G variant— meaning that in a lab setting, antibodies from a vaccinated or infected individual were less likely to destroy BF.7 than the original Wuhan virus that spread worldwide in 2020.
  • A higher neutralisation resistance means there is a higher likelihood of the variant spreading in a population and replacing other variants
• XBB variant:
  • XBB is a recombinant of two Omicron sub-variants, BA.2.10.1 and BA.2.75.
  • XBB is more immune evasive and more likely to cause re-infection or breakthrough infections in people.
  • Like any other Omicron variant XBB is known to affect the upper respiratory tract.
  • The XBB variant is likely to lead to a fever, cough, and cold.

What is a recombinant variant:

• About:
  • Besides the errors in the virus genome, recombination is another process through which a virus increases its genetic diversity.
  • Recombination occurs when, in extremely rare situations, two different lineages of the virus co-infect the same cell in the host and exchange fragments of their individual genomes.
  • This generates a descendent variant having mutations that occurred in both the original lineages of the virus.
  • Recombination of lineages happens in a variety of other viruses, including those that cause influenza, as well as other coronaviruses.
  • Such recombination events typically occur when two or more lineages of SARS-CoV-2 may be co-circulating in a certain region during the same time period.
  • This co-circulation of lineages provides an opportunity for recombination to occur between these two lineages of SARS-CoV-2.
• Impact:
  • Although recombination has been detected in SARS-CoV-2, it has not yet impacted public health in a unique way.
  • There is little evidence to suggest that recombinant lineages have a varied clinical outcome compared to the currently dominant Omicron variant.
  • It is certain at this point in time that more data will be needed to ascertain the impact of these lineages on the epidemiology of COVID-19.

Conclusion:

• Since recombinations are extremely rare occurrences, it is unclear how and why the viruses recombine.
• It is, therefore, important to track the recombination of SARS-CoV-2 lineages because it may lead to the generation of a viral lineage that is better at infecting people or transmitting from host to host.
• Monitoring circulating SARS-CoV-2 genomes for evidence of recombination will help gain a better understanding of the ongoing evolution of SARS-CoV-2.
• It will also provide information if a more “concerning” variant of the virus were to emerge.

Pic Courtesy: The Hindu

Content Source: The Hindu

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