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Inside the COVID-19 mutant: The 'drift' of a virus

The UK has identified a fast-spreading new variant of coronavirus that is 70% more transmissible than existing strains. A similar mutation was also reported from South Africa and countries like Netherlands and Denmark

twitter-logoPB Jayakumar | December 22, 2020 | Updated 18:11 IST
Inside the COVID-19 mutant: The 'drift' of a virus
The two new variants have affected Kent and South East England the most

Despite the new COVID-19 mutant triggering fresh global panic with nations re-imposing travel bans, scientists say it is too early to predict the virus is going to cause a 'second wave' or make recently-developed vaccines useless.

The UK has identified a fast-spreading new variant of coronavirus that is 70% more transmissible than existing strains. A similar mutation was also reported from South Africa and countries like Netherlands and Denmark.

The scientists have observed three major mutations of the COVID-19 virus so far:

  • D614G (Amino acid 614 on spike protein)
  • VUI 2020-12/01
  • N501Y

D614G was responsible for the fast spread of the virus in Europe, the US and the rest of the world. The other two (VUI 2020-12/01 and N501Y) are the current ones causing panic in the UK. But, there is also what's called the 'South Africa drift', in which three mutations happened in the genetic make up of the virus.

The two new variants have affected Kent and South East England the most. They saw the disease rate spike from 100 cases per 100,000 population in week 41 to over 400 per 100,000 in week 50 of 2020.

Total 1,108 individuals were identified with the novel variant in England until December 13, with the earliest case identified dating back to September 20. The new strain has also been seen in other countries, including Denmark and the Netherlands.

The United Kingdom has an established SARS-CoV-2 genome sequencing consortium called COG-UK, which consists of the national public health institutes, National Health Service organisations, academic institutions, and the Wellcome Sanger Institute, which tacks virus mutations.

Experts say it is early to predict whether the vaccines would be effective or not against the new strains. The vaccine roll out has just started in countries like the US and UK.

Genetic mutation happens with viruses and scientists typically tweak vaccine combinations from time to time to counter mutated viruses. The tweaking of combinations is followed in the case of influenza vaccines.

When a new virus strain arises, three main factors that need to be watched are transmissibility, pathogenicity (ability to cause the disease) and immunogenicity (to provoke the body immune response).

So far scientists have identified 501 different variants of viruses which are more transmissible, but are yet to prove if they cause the disease.

Another factor to look at is 'antigenic drift' (minor mutation) and 'antigenic shift' (major mutations). Both new strains (VUI 2020-12/01 and N501Y) are antigenic drift and not antigenic shift. In minor mutations, small changes in the genes of a virus lead to changes in surface proteins of the virus. The surface proteins are recognised by immune system and are capable of triggering a response, including production of antibodies that can block the infection. Experts say changes associated with antigenic drift happen continually over time as virus replicates.

Most vaccines are designed to target these spike proteins, which prevent infection. However, the small changes associated with 'antigenic drift' can accumulate over time and result in viruses that are genetically different.

It is also possible for a single (or small) change in a particularly important location on the protein to result in antigenic drift (major mutation).

When antigenic drift occurs, the body's immune system may not recognise and prevent sickness caused by the newer viruses. As a result, a person becomes susceptible to infection. The existing antibodies won't recognise and neutralise the newer viruses. Such mutations happen in influenza; that's why people can get flu more than once.

It is also the main reason why flu vaccine compositions are reviewed and updated each year to keep up with evolving influenza viruses, explains Dr K K Aggarwal, President Confederation of Medical Associations in Asia and Oceania(CMAAO).

The other type of possible change is called 'antigenic shift', an abrupt major change in a virus, resulting in new proteins that infect humans. This shift creates subtype viruses. The shift can also happen when a virus from an animal population gains ability to infect humans. But this has not been seen in COVID-19 cases.

Such animal-origin viruses can contain a protein that is so different from the same subtype in humans that most people do not have immunity to the new virus. Such a shift occurred in the spring of 2009, when an H1N1 virus with genes from North American Swine, Eurasian Swine, humans and birds emerged to infect people and quickly spread, causing a pandemic. Most people had little or no immunity against the new virus.

While influenza viruses change all the time due to antigenic drift, antigenic shift happens less frequently. Influenza pandemics occur very rarely and there have been four pandemics in the past 100 years. Type A influenza viruses undergo both antigenic drift and shift and are the only influenza viruses known to cause pandemics, while influenza type B viruses change only by the more gradual process of antigenic drift, says Dr Aggarwal.

Also Read: Mutant COVID-19 strain not seen in India yet: NITI Aayog member

Also Read: Delhi likely to receive first shipment of COVID-19 vaccine next week

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