There appear to be two strains of the new coronavirus that has killed over 3,000 since last December, with one more "aggressive" than the other, according to Chinese scientists. But experts stress this should not be a cause for concern for the general public.
By analysing the viral DNA from 103 people infected with the virus, the team found the germ which causes COVID-19 seems to have evolved into two major types which they called "L" and "S."
It is normal for viruses to mutate. The tiny microbes are made up of a protein coat filled with genetic material and need to get inside the cells of a host—like a human—to reproduce. If the immune system of a potential host learns how to stop the virus from entering its cells, the bug must change to survive.
In the case of the new coronavirus, the team found L appears to have derived from the older S, and made up around 70 percent of the cases they studied. S seemed to be "less aggressive," while with L "more aggressive," and able to spread quicker in comparison.
The team believes L was more prevalent in the early stages of the outbreak in the central Chinese city of Wuhan, the capital of Hubei province, where the disease is thought to have first appeared in December 2019.
According to the paper published in the journal National Science Review: "Human intervention may have placed more severe selective pressure on the L type, which might be more aggressive and spread more quickly." Selective pressure is a strain placed on an organism that forces it to evolve in order to survive
The virus which causes COVID-19 is called SARS-CoV-2, but not to be confused with the SARS virus. Experts decided on this name because the COVID-19 virus triggers similar symptoms to the SARS virus.
The researchers wrote in their study: "We propose that, although the L type newly evolved from the ancient S type, it transmits faster or replicates faster in human populations, causing it to accumulate more mutations than the S type. Thus, our results suggest the L might be more aggressive than the S type due to the potentially higher transmission and/or replication rates."
However, they stressed: "The data examined in this study are still very limited, and follow-up analyses of a larger set of data are needed to have a better understanding of the evolution and epidemiology of SARS-CoV-2."
They also found evidence to suggest a person can be infected by the two types of the virus, by looking at a sample from a 63-year-old patient living in Chicago thought to have returned from Wuhan on January 13. But the team said it is unclear whether the woman was infected multiple times. They made a similar finding by looking at a sample from a 44-year-old man on Australia's Gold Coast, which is among affect areas as shown in the Statista map below.
Questions still remain, the team said, as to which strain is more virulent, and whether L evolved from S in humans, or in the animal that hosted it before it jumped to people.
Ian Jones, professor of virology at the University of Reading, told Newsweek the work is "an early study of the evolution of the new virus." Their "conclusions are reasonable, but they are not supported by any biological experiments so they remain plausible but not proven," he said.
Jones argued the scientists were ill-advised to use to term "aggressive, which doesn't mean much biologically."
"What they mean is that the virus transmits more easily, not that it causes worse disease," he said. "In addition the 70/30 split in the types is not that great and some of their data show both types in the same patients.
"Overall (other studies included) it seems to me the virus is remarkably stable. That's bad news in that it is not getting any less infectious, but good news in the sense that what we have is probably as bad as it will ever get," said Jones.
That "means that a vaccine made now will still be relevant in six or nine months time when it might eventually appear," he explained.
In an apparent attempt to allay fears that the study might raise at a time of heightened anxiety, virologist Ian Mackay, adjunct Associate Professor at the University of Queensland, Australia, tweeted: "This is just humans seeing patterns and describing them at this stage."
He compared the viruses to a family splitting and moving to Canada and the U.S.: they would both still be human, but would speak different variations of the same language and be culturally different.
"They'd have made subtle adaptations to their environment to fit in and stand out less," he said.
Richard Neher, a biologist and physicist at the Biozentrum of the University of Basel, tweeted that the split could be down to the L group being sampled more in Wuhan, making it appear more deadly.
"Rapidly growing local outbreaks get sampled intensively and result in overrepresentation of some variants. This happened early on around the Wuhan Seafood market and now with the Italian outbreak," he said, adding: "Any statistical inference needs to account for such sampling biases and just taking values at face values will result in wrong, misleading, or downright dangerous inferences."
SARS-CoV-2 is what is known as an RNA virus, which describes how it carries its genetic information. Associate Professor Stephen Griffin of the Leeds Institute of Medical Research and chair of the virus division at the Microbiology Society told the U.K.'s The Telegraph: "It is usually the case that when RNA viruses first cross species barriers into humans they aren't particularly well adapted to their new host—us.
"Thus, they usually undergo some changes allowing them to adapt and become better able to replicate within, and spread from human-to-human," he said.