Science and Technology article
🔷 Viruses, their variants, and vaccines
✅ 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.
🟡 Why do viruses mutate?
✅ 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, the errors in DNA virus genomes can be corrected by the error-correcting function of cells in which they replicate.
✅ But there are no enzymes in cells to correct RNA errors. Therefore, RNA viruses accumulate more genetic changes (mutations) than DNA viruses.
🟡 How much has SARS-CoV2 mutated?
✅ Coronaviruses have an RNA genome with two unique features.
✅ At 30,000 nucleotides (nucleic acid units) they have the largest genome among RNA viruses.
✅ This allows coronaviruses to produce an enzyme that can correct RNA replication errors.
✅ Consequently, coronaviruses have rather stable genomes, changing about a thousand times slower than influenza viruses, which too are RNA viruses that cause respiratory illness.
◼️ A mutation called D614G emerged in late January 2020 to change the amino acid at position 614 in the virus’ Spike protein from aspartate (D) to glycine (G).
◼️Because this variant infected and replicated better and produced ‘fitter’ viruses, it now accounts for over 99 per cent of the virus circulating globally.
◼️Other mutations are now emerging in this background.
✅ 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.
✅ Three key RBD mutations — K417N/T, E484K, and N501Y — are found in variants that emerged in South Africa and Brazil.
✅ The UK variant has the N501Y mutation, but has another called P681H outside the RBD, which too increases infectivity.
🟡 How are vaccines tested for effectiveness 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.
✅ 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.
🟡 Can new vaccines be developed to fight variants?
✅ There is no evidence
that current vaccines are failing. But this has to be watched carefully.
✅ Both Moderna and Pfizer/BioNTech have agreed that their vaccines offered reduced protection against the South African variant.
✅ Should new vaccines be needed, the mRNA platform offers the best chance of speedy development.
✅ These vaccines were the first to receive emergency use approval, and have already been administered to millions of people globally.
🟡 What should India do in this situation?
✅ India till now reported only the UK variant viruses.
✅ 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 only way to catch emerging variants — whether imported or homegrown — is increased genomic surveillance.
✅ 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.
Source: The Indian EXPRESS https://IndianEXPRESS.com