No sign of big mutations in coronavirus strains, study finds
- Italian researchers say there is little difference between the varieties circulating worldwide but monitoring should continue
- Results bolster prospects for a vaccine to fight the pathogen, co-author says
Researchers from the University of Bologna in Italy examined 48,635 genomes of Sars-CoV-2, the official name for the virus that causes the disease Covid-19, collected by labs from around the world and published the results in a paper in the peer-reviewed journal Frontiers in Microbiology at the end of last month.
The researchers identified six strains of the virus but found no significant clinical or molecular differences between them.
“The Sars-CoV-2 coronavirus is presumably already optimised to affect human beings, and this explains its low evolutionary change,” Federico Giorgi, assistant professor of bioinformatics at the University of Bologna, said.
“This means that the treatments we are developing, including a vaccine, might be effective against all the virus strains,” said Giorgi, who coordinated the study.
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The six strains of the virus included the L strain, the one first reported in the central Chinese city of Wuhan in December 2019.
The researchers said the L strain was disappearing and the G strain had become the most widespread. The G strain and subsequent mutations were mostly found in Europe and North America, and accounted for 74 per cent of all the gene sequences analysed, according to the paper.
The variability of the virus was about seven mutations per sample, less than half the variability of common influenza, the study said.
The findings were encouraging for the development of vaccines, which depended on recognising the viral features of Sars-CoV-2, said co-author Daniele Mercatelli, from the university’s pharmacy and biotechnology department. If these viral features changed, vaccines could become less effective.
Mercatelli said an effective vaccine would train the immune system to recognise and promptly fight Sars-CoV-2 inside the body, usually by letting the immune system distinguish some peculiar viral features, such as the spike protein which helps the virus bind to human proteins.
“These features work like a flag. When the immune system recognises this flag, it can respond to it,” he said.
“The rise of mutations changing these viral features may potentially have an impact on vaccine efficacy, because the flag can become so different from the original one that the immune system loses its ability to recognise it.”
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“There is currently no strong evidence of the existence of a Sars-CoV-2 strain characterised by a higher infectious potential,” he said.
“However, some viral subpopulations are growing faster worldwide, thus it is important to keep on monitoring Sars-CoV-2 mutations to understand if some variants may confer an advantage to the virus or to prevent the rise of an aggressive strain.”
The results of the paper also confirmed research by Malik Peiris, a professor of virology at the University of Hong Kong.
“Sars-CoV- 2 is relatively stable genetically, so very few mutations. Also, the key protective target in the virus spike, to which a neutralising antibody is directed, does not have much ability to mutate,” Peiris said.
He said the seven or so mutations per sample found in the University of Bologna study could even be lower.
“If you look at mutation rates between specimens when the virus passed from one person to the next, often there is zero mutation. So in closely related clusters often there is zero or one mutation,” Peiris said.