Coronavirus has mutated into a more aggressive strain, scientists find

Scientists have discovered a second coronavirus strain causing infections, indicating the disease has mutated at least once.

An image of the coronavirus, taken by a transmission electron microscope. Picture: National Institutes of Health

Scientists have identified two strains of the novel coronavirus causing infections, one more aggressive than the other, indicating that the disease has mutated at least once.

In a new study published as Britain was told to expect a pandemic, Chinese researchers suggest that after COVID-19 crossed into humans, the original strain evolved into a new type and both of these are now circulating.

Although further research is needed, the preliminary study, carried out at Peking University’s school of life sciences and the Institut Pasteur of Shanghai, sheds some light on how the disease is evolving.

The researchers identified two strains, with the more aggressive accounting for 70 per cent of those they analysed and a less aggressive strain making up the rest.

The less aggressive strain, identified as ‘S’, appeared to be the ancestor of the more aggressive one, ‘L’.

Strain ‘L’ was found to be more prevalent at the start of the original outbreak in Wuhan but began to subside in early January. The S type has since become more common.

The study, published in the journal of the Chinese Academy of Sciences National Science Review, suggests this could be due to the rush to treat patients infected with the L strain, whose symptoms are easier to detect.

“If the L type is more aggressive than the S type, why did the relative frequency of the L type decrease compared to the S type in other places after the initial breakout in Wuhan?” the researchers asked.

“One possible explanation is that, since January 2020, the Chinese central and local governments have taken rapid and comprehensive prevention and control measures.

“Human intervention may have placed more severe selective pressure” on the aggressive strain, the researchers wrote, while the less aggressive strain “might have increased in relative frequency due to relatively weaker selective pressure”.

The scientists said that due to the small sample size more research is needed. “These findings strongly support an urgent need for further immediate, comprehensive studies that combine genomic data, epidemiological data and chart records of the clinical symptoms of patients with coronavirus disease 2019,” the authors wrote.

Experts not directly involved in the study said its findings were interesting but cautioned against drawing firm conclusions from such preliminary research.

“It’s difficult to confirm studies like this without a direct side-by-side comparison of pathogenicity and spread in, ideally, an animal model, or at least a greatly extended epidemiological study,” said Stephen Griffin, a professor and expert in infection and immunity at Leeds University.

News of the apparent mutation was the second-highest trending topic on the Chinese social media site Weibo yesterday and was shared by Chinese state media.

Yesterday one of China’s top medical associations said that the median incubation period of the coronavirus is five to seven days and the maximum 14 days.

The remarks by Du Bin, chairman of the critical care medical branch of the Chinese Medical Association, are the most conclusive assessment of the virus’s incubation period by a government-affiliated medical organisation to date, Reuters reports.

New coronavirus cases in China have begun to fall following strict restrictions, including transport suspensions and the extension of the lunar new year holiday.

THE TIMES