SARS-CoV-2 is a virus that can mutate very quickly and dramatically, with major mutations occurring about every six months. There have been four major mutations since COVID-19 broke out in Wuhan, China, a little more than two years ago. Each time a new mutation has appeared, its rate of transmission has more than doubled. The new variant then becomes the dominant virus in the world and the previous prevalent variant mysteriously disappears from the population.
For example, after the Alpha variant of SARS-CoV-2 emerged in the UK in November 2000 and became the dominant strain in the world, the original Wuhan variant known as D614G disappeared. Then the UK variant disappeared after the Delta variant emerged in India in May last year.
The Omicron variant was first recorded in South Africa on Nov. 24 last year, and within a short time the Indian Delta variant has nearly disappeared and been replaced by Omicron as the dominant strain in the world.
The Omicron variant has 34 genetic mutations in its spike protein, which include some of the important mutations seen in the Delta variant. Similarly, Delta has 13 mutations, which include some of the important mutations of the British Alpha variant.
In turn, the British Alpha variant has 23 mutations that include mutations seen in D614G. The original Wuhan variant, D614G, only has one mutation, which is also found in the Alpha, Delta and Omicron variants.
This situation can be explained by immunology. People who got infected with Alpha produced antibodies that neutralized D614G, so the D614G variant could no longer be transmitted among the population.
The same thing happened when Delta appeared — Alpha could no longer be transmitted. Similarly, Delta has mostly disappeared since the emergence of the Omicron variant, so that people are now only getting infected with Omicron.
According to a research paper published late last year, a team of scientists in South Africa, including virologist Alex Sigal, conducted an experiment in which they selected eight vaccinated people and seven unvaccinated people who were confirmed to be infected with the Omicron variant.
Analysis and comparison of the neutralizing antibodies produced in the bodies of vaccinated and unvaccinated individuals showed that neutralization of Omicron increased 14.4-fold in vaccinated participants, while neutralization of Delta increased 4.4-fold, but the immune response in unvaccinated participants was more variable.
This means that vaccinated and unvaccinated individuals have enhanced production of antibodies against Delta after being infected with Omicron, so the Delta variant cannot continue to spread among the population.
Since the South African Omicron variant already has 34 genetic mutations in its spike protein, it is unlikely that it will undergo any further major mutations. That being the case, it should not be long before COVID-19 starts behaving like influenza or the common cold.
Lai Shiow-suey is a professor emeritus of National Taiwan University’s Department of Veterinary Medicine.
Translated by Julian Clegg
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