Scientists discover two major subtypes of COVID-19

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."