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Explained: Are there two types of COVID-19 viruses?

Through their study, researchers have proposed that SARS-CoV-2 can be classified into two types: L and S, but it remains to be seen if the L type evolved from the S type in humans or in an intermediate host.

By: Explained Desk | New Delhi | Updated: March 6, 2020 11:46:02 am
coronavirus, coronavirus two strains, COVID-19 virus, new study on COVID-19 virus, new study on coronavirus, indian express, express explained A man wears a mask in Hyderabad on March 5. India has so far reported 30 confirmed coronavirus cases. (Photo: AP)

A preliminary study conducted by researchers from Peking University’s School of Life Sciences and the Institut Pasteur of Shanghai, which is under the Chinese Academy of Sciences, has found two strains of the SARS-CoV-2 virus, behind the current coronavirus infection crisis.

As per the study, one of these strains is more aggressive than the other, and was associated with 70 per cent of the analysed strains. The researchers have also said that the prevalence of the more aggressive strain decreased after January 2020.

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For the study, whose manuscript has been accepted by the National Science Review, the researchers downloaded 103 publicly available SARS-CoV-2 genomes. After analysis, they identified mutations in 149 sites across the 103 sequenced strains.

Within the 103 genomes, one of the two strains of the SARS-CoV-2 was more prevalent. The researchers have called the two strains ‘L’ and ‘S’ types.

Further, the researchers maintain that while the L type was prevalent in over 70 per cent of the cases analysed, the S type of the virus is the ancestral version, which means that the L type is derived from the S type and it transmits and replicates faster in human populations, researchers conclude. Because of this higher transmission rate, the L type is considered to be more aggressive.

Explained: Are there two types of COVID-19 viruses? Outside a coronavirus facilitation centre in New Delhi. (Express Photo: Tashi Tobgyal)

Significantly, of the 27 viruses out of 103 isolated by the researchers that were from Wuhan, 26 were L type (96.3 per cent). Among the 73 viruses isolated from outside Wuhan, 45 were L type (61.6 per cent) and 28 were S type.

The 26 samples isolated before January 7, 2020 were from Wuhan. Among the 74 viruses isolated from January 7, one was from Wuhan, 33 were from other locations in China and 40 were from patients outside China.

Therefore, the L type of the strain was more prevalent before January 7, 2020.

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The researchers also pose the question that if the L type was more aggressive than the S type, why did its frequency decrease in other places after the initial breakout in Wuhan? To this, the researchers propose that due to heightened human interventions beginning in January 2020, the L type might have faced “selective pressure”, which the S type did not because of different epidemiological features of the two strains.

They, however, caution that their hypothesis is based on genomes that were collected from different locations at different points in time, due to which the results may not be comprehensive.

Explained: Are there two types of COVID-19 viruses? Students wear masks at a school.

Essentially, through their study, the researchers have proposed that SARS-CoV-2 can be classified into two types: L and S, but it remains to be seen if the L type evolved from the S type in humans or in an intermediate host.

It is also not clear if the L type is more virulent than the S type. “… our analyses of 103 sequenced SARS-CoV-2 genomes suggest that the L type is more aggressive than the S type and that human interference may have shifted the relative abundance of L and S type soon after the SARS-CoV-2 outbreak,” the researchers have said.

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