3.SARS-COV-2 NEW VARIANTS
- SARS-CoV-2variants 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 virusis responsible for causing the coronavirus disease (Covid-19).
MEANING OF MUTATION:
- Mutation is an alte ration in the genetic material (the genome) of a cellof a living organism or of a virus that is more or less permanent and that can betransmitted to the cell’s or the virus’s descendants.
- The genomes of organisms are all composed of Deoxyribonucleic Acid (DNA), whereas viral genomescan be of DNA or Ribo Nucleic Acid (RNA).
RNA MUTATION VS DNA MUTATION:
- When cells multiply, the DNA wi thin them replicatesas well, to make copies for the new cells. During replication, random errorsare introduced into thenew DNA.
- While the errors in DNA virus genomes can be corrected by the errorcorrectingfunction 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:
- While most mutations are deleterious to the virus, if some allow a selective advantage,say better infectivity, transmission, or escape from immunitythen the new viruses out-compete the older ones in apopulation.
FOR EXAMPLE: A mutation called D614Gemerged in January 2020 to change the amino acidat 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 proteinthat binds to a human proteinto 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 theimmune response made by vaccines.
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 theoriginal virus, are tested to determine whether the variant viruses evade antibodies.
- The effectiveness of a serum or antibody is expressed as an inhibitoryconcentration (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 vaccinesto cover these variants.
- There is also proof of several re-infectionswith the variant in South Africa, driven by the ability of new variants to evade immunity developed against the original virus.
- Only the UK variant viruses have so far been reported from Indiaand 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 serumfrom recipients of their vaccine, Covaxin, againsta 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 surveillanceis a step in the right direction.
- Genomic surveillancecan generate a rich source of information for tracking pathogen transmission and evolution on both national and international levels.