Chinese scientists have discovered the novel coronavirus has evolved into two major subtypes. Experts believe investigating the differences and features of these subtypes may help evaluate risks and formulate better treatment and prevention plans.
The two subtypes are named L and S. The L type is more aggressive and was prevalent in the early stages of the outbreak in Wuhan, Central China's Hubei province. But instances of the S type, which is older and less aggressive, have increased in frequency recently, thus possibly explaining the disease's slowing momentum in China.
In the study, scientists identified 149 mutations in the 103 sequenced genomes of the novel coronavirus. Experts believed these mutations took place recently and 83 of these mutations are nonsynonymous, meaning they can alter the amino acid sequence of a protein and may result in a biological change in the organism.
The study, titled "On the Origin and Continuing Eolutionof SARS-CoV-2", was published on China's peer-reviewed journal, National Science Review, on Tuesday. The study was done by scientists from Peking University, Shanghai University and the Chinese Academy of Sciences.
However, the authors highlighted the fact the data examined in the study is very limited. How L type strains evolved from S type, as well as how these mutations would affect the transmission and pathogenesis of the virus,are still unknown.
"There is a strong need for further immediate, comprehensive study," they wrote.
In the paper, the scientists said the 103 novel coronavirus strains studied could be divided into two major types called L and S, with L being more prevalent and covering 70 percent of the strains examined. The S types are the ancestral strains, but the L types are believed to be more aggressive, multiply faster in humans and can spread more quickly than their ancestors.
Moreover, the L type is significantly more prevalent in Wuhan than in other places, according to viral samples. After January, however, the L type's frequency of appearance decreased compared to the S type, which might explain the virus's slowing momentum in China.
Experts speculated this may be due to Chinese central and local governments taking rapid and comprehensive prevention measures that caused severe selection pressure against the L type. However, this hypothesis requires further study, they added.
Scientists also found most patients caught either the L or S type of novel coronavirus strain. But there might be exceptions to the rule that should be followed with further research.
For example, the study said a 63-year-old female patient in Chicago had likely contracted both L and S types of novel coronavirus strains when she traveled in Wuhan and returned to the United States on Jan 13. A patient from Australia also was discovered to have possibly been carrying at least two different strains of the coronavirus when he returned.
"These findings evince the developing complexity of the evolution of SARS-CoV-2 infections," the paper said. "Further studies investigating how the different alleles of SARS-CoV-2 viruses compete with each other will be of significant value."
This week, scientists from Brazil and United Kingdom said the genetic sequence of the virus collected from the first patient in Latin America is slightly different than the strain from Wuhan by three mutations. Two of these mutations draw the virus closer to a strain detected in Germany.
A virologist in Beijing who spoke on condition of anonymity said the purpose of the paper is to present "a fascinating finding" that the novel coronavirus already had two different subtypes existing in nature with different effects on humans.
"It is still too early to say if the virus has mutated into something more sinister, or more benign, for all we know the mutations might take place on part of the genome that do nothing at all," he said.
"The more we study the virus, the more secrets we unraveled. An interesting question we can explore next is whether patients that exhibited no symptoms werethat way because they were infected with the older but milder S type strains. Only more research can tell."
have concluded that it is "just like the flu" 
