SARS-CoV-2 New Variants

• 30 Jan 2021

Why in News

SARS-CoV-2 variants have emerged independently in several countries, and the latest research indicates that the virus is changing quickly (mutatition) and it may continue to develop towards evading currently available vaccines.

• SARS-CoV-2 virus is responsible for causing the coronavirus disease (Covid-19).

Key Points

• Meaning of Mutation:
  
  • Mutation is an alteration in the genetic material (the genome) of a cell of a living organism or of a virus that is more or less permanent and that can be transmitted to the cell’s or the virus’s descendants.
  • The genomes of organisms are all composed of Deoxyribonucleic Acid (DNA), whereas viral genomes can be of DNA or Ribo Nucleic Acid (RNA).
• RNA Mutation vs DNA Mutation:
  
  • When cells multiply, the DNA within them replicates as well, to make copies for the new cells. During replication, random errors are introduced into the new DNA.
  • While the errors in DNA virus genomes can be corrected by the error-correcting function of cells in which they replicate, there are no enzymes in cells to correct RNA errors. Therefore, RNA viruses accumulate more genetic changes (mutations) than DNA viruses.
• Significance of Mutation:
  
  • Evolution:
    
    • While most mutations are deleterious to the virus, if some allow a selective advantage, say better infectivity, transmission, or escape from immunity then the new viruses out-compete the older ones in a population.
    • For example: A mutation called D614G emerged in January 2020 to change the amino acid at a position in the coronavirus’ Spike protein.
      
      • Because this variant infected and replicated better and produced ‘fitter’ viruses, it now accounts for over 99% of the virus circulating globally. Other mutations are now emerging in this background.
      • It is the coronavirus spike protein that binds to a human protein to initiate the process of infection.
      • Changes here could possibly affect how the virus behaves in terms of its ability to infect, or cause severe disease, or escape the immune response made by vaccines.
• Distinct features of RNA Genome of Coronavirus:
  
  • Coronaviruses have an RNA genome with two unique features:
    
    • Largest Genome:
      
      • At 30,000 nucleotides (nucleic acid units) they have the largest genome among RNA viruses.
    • Stability:
      
      • Coronaviruses have rather stable genomes, changing about a thousand times slower than influenza viruses, which too are RNA viruses that cause respiratory illness.
• Recent RBD Mutations in Coronavirus Variants:
  
  • Three key Receptor-Binding Domain (RBD) mutations K417N/T, E484K, and N501Y are found in variants that emerged in South Africa and Brazil.
    
    • The UK variant has the N501Y, P681H mutation.
  • Viruses with mutations within the receptor-binding domain (RBD) of the Spike protein have the most potential to evade antibodies that develop as a result of natural infection or vaccination.
  • The RBD binds the cellular receptor allowing the virus to infect cells, and anti-RBD antibodies neutralise the virus.
• Vaccine Test Against Emerging Variants:
  
  • Indirect tests are done in laboratories to assess if an emerging variant might escape antibodies developed after a natural infection or vaccination.
    
    • Serum (the blood components that contain antibodies) from recovered patients or vaccinated people, and antibodies known to neutralise the original virus, are tested to determine whether the variant viruses evade antibodies.
    • The effectiveness of a serum or antibody is expressed as an inhibitory concentration (IC) or plaque reduction neutralisation titer (PRNT) value.
    • The IC50 or PRNT50 value is the reciprocal dilution of serum or antibody that neutralises 50% viruses in the sample.
• Efficacy of Vaccine Against Emerging Variants:
  
  • Both Moderna and Pfizer/BioNTech have agreed that their vaccines offered reduced protection against the South African variant. The two companies are reported to be working on developing fresh vaccines to cover these variants.
  • There is also proof of several re-infections with the variant in South Africa, driven by the ability of new variants to evade immunity developed against the original virus.
• India’s Case:
  
  • Only the UK variant viruses have so far been reported from India and that too, in travellers. There is no reported local transmission.
  • The evidence so far suggests that current vaccines would still protect against the UK variant, even if with reduced efficacy.
    
    • Scientists from ICMR-National Institute of Virology and Bharat Biotech tested serum from recipients of their vaccine, Covaxin, against a UK variant.
    • The results show no significant difference, suggesting that the vaccine would work equally well on the UK variant.
  • With cases already going down, India should strictly implement masks and limit crowds while aggressively tracing contacts of people infected with the UK variant.
  • India must also be vigilant of people with a history of travel to South Africa since October 2020, and Brazil since December 2020.
  • The setting up of an inter-ministerial group ‘Indian SARS-CoV-2 Genomics Consortium (INSACOG)’ to increase genomic surveillance is a step in the right direction.
    
    • Genomic surveillance can generate a rich source of information for tracking pathogen transmission and evolution on both national and international levels.

Source:IE