SARS-CoV-2 variants have emerged independently in several countries, and research published over the past week indicates that the virus is changing more quickly than was once believed.
Try this PYQ:
Q.H1N1 virus is sometimes mentioned in the news with reference to which one of the following diseases?
(a) AIDS
(b) Bird flu
(c) Dengue
(d) Swine flu
Mutation of Virus
- Mutation, 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.
- Like all life, viruses carry a genetic code in the form of nucleic acids — either DNA or RNA.
- 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, much like spelling errors when we write.
- 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.
Effect of mutation on the virus
- Evolution requires not just mutations, but also selection.
- 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.
- The mutations can be synonymous (silent) or non-synonymous (non-silent); the latter also changes an amino acid (protein building block) at that position in the coded protein.
Mutations in COVID
- As of January 26, about 29,000 infections are attributed to UK variants from 63 countries, many due to local transmission.
Why is it harmful?
- 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 neutralize the virus.
- Such mutations were recently found in variant viruses that emerged in the UK, South Africa and Brazil.
Testing of mutation
- Indirect tests are done in laboratories to assess if an emerging variant might escape antibodies developed after natural infection or vaccination.
- Serum (the blood components that contain antibodies) from recovered patients or vaccinated people, and antibodies are known to neutralize the original virus, are tested.
- Serial dilutions of the serum or antibodies are separately mixed with a fixed amount of the original and variant viruses, and the mixture is added to cells in culture.
- After a period of incubation, cells are washed and stained. Cells infected and killed by viruses multiplying within them appear as clear zones (plaques) on a dark background.
- The effectiveness of 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 per cent viruses in the sample.
India’s response
- Only the UK variant viruses have so far been reported from India — and that too, in travellers.
- There is no reported local transmission, but considering its increased infectivity, this is likely to happen.
- The evidence so far suggests that current vaccines would still protect against the UK variant, even if with reduced efficacy.
- The evidence at this time, though of concern, does not indicate that current vaccines are failing.
- But this has to be watched carefully, and all efforts made to limit transmission between people, which drives mutations and the emergence of variants.
