As the coronavirus swept the globe, the coronavirus picked up random changes in its gene sequence. Most of these mutations, like the pointless typos in the script, made no difference in the behavior of the virus.
However, one mutation near the beginning of the pandemic made a difference, and multiple new discoveries suggested that it helped the virus spread more easily from person to person, making it more difficult to stop the pandemic.
The mutation, known as 614G, was first discovered in eastern China in January and has since spread rapidly throughout Europe and New York City. Within a few months, this variant dominated most of the world and replaced other variants.
Scientists have been arguing for months about why. Researchers at the Los Alamos National Laboratory claimed in May that the variant probably evolved its ability to infect people more efficiently. Many were skeptical, claiming that the variant might simply have been lucky, and often happened to appear in large-scale epidemics such as Northern Italy, which caused outbreaks elsewhere.
However, many new studies, such as in-depth genetic analysis of development and laboratory studies with hamsters and human lung tissue, have found that the mutant virus actually has clear advantages and was detected in Wuhan. We support the view that it infects people more easily than its variants. , China.
There is no evidence that a coronavirus with the 614G mutation causes more serious symptoms, kills more people, or complicates vaccine development. Also, the findings do not change the reality that places that implemented swift and proactive blockades and encouraged measures such as social distance and masks were far better than those that did not.
However, subtle changes in the viral genome appear to have had a significant spillover effect, said David Engeltaler, a geneticist at the Translational Genomics Institute in Arizona. “When everything is said and done, it’s possible that this mutation caused a pandemic,” he said.
Most researchers, including Dr. Engeltaler, believe that the first outbreak of the virus would have spread around the world without mutations. The original variant discovered in Wuhan, China in late 2019 was already highly contagious, he said. However, the mutation spread even faster than it would have been without the pandemic.
Scientists are particularly cautious in this area of virology.
Laboratory studies have shown that mutations in the Ebola virus that have spread to West Africa since 2013 increase the infectivity of tissue culture. However, that conclusion did not lead to increased transmission in laboratory studies with animals. Also, some experts said the effects of the 614G mutation could be modest compared to other factors such as the percentage of social distance.
But new evidence from UK and US research groups has changed the minds of many initially skeptical scientists.
According to one study, outbreaks in the British community grew faster when sown with the 614G variant than when sown with Wuhan ancestors. According to another report, hamsters infected each other sooner when exposed to the mutant. And third, the mutants infected human bronchial and nasal tissues in cell culture dishes much more efficiently than their ancestors.
Trevor Bedford, an associate professor at the Fred Hutchinson Cancer Research Center and the University of Washington, said he was better off collecting findings from a variety of research disciplines.
“I’m convinced that I’m seeing the same thing over and over again,” said Dr. Bedford. “At this point, I think it’s real.”
Dr. Bedford and other scientists were impressed with the new study, but said it was still unclear whether the inherent benefits were the main reason for the global domination of this variant.
Christian Andersen, a geneticist at Scripps Research in La Jolla, said the study showed that the mutants were more contagious, but believed that the differences were subtle.
Still, Dr. Andersen said the higher infectivity of the variant could help explain why some countries that first succeeded in containing the virus later became more susceptible to the virus. I did. The virus was “more difficult to contain than it was in the beginning,” he said.
“What you were doing before may not be enough to control it,” Dr. Andersen said. “Don’t necessarily expect the enemy two months ago to be the next enemy.”
Around the world, the advent of the 614G has created both serious scientific debate and avoidance of predominantly political criticism. Vietnamese and Thai government officials succeeded in containing ancestral stocks despite an influx of Chinese visitors earlier in the year, but subsequent outbreaks were partly the result of the 614G virus. It was suggested that there was a possibility.
Thira Waratanarat, associate professor of Chulalongkorn University School of Medicine in Bangkok, said Thailand has managed both variants of the virus over the past year through measures such as strict quarantine of returnees, bans on foreign tourists and masks. He said he had continued to do so. Still, he said there were concerns about a resurgence in the area.
“I’ve seen some countries that seem to control it, such as Vietnam, South Korea, and Japan,” said Dr. Thira. “But then there was a second wave.”
In Vietnam, a virus with the 614G mutation was first identified in the central coastal city of Da Nang about 100 days later, and no cases of local infection have been reported, he said. The outbreak quickly spread to 10 cities and states. In Singapore, he said, the mutated virus spread to crowded dormitories for migrant workers.
“When the mutated virus lives in a large group, it spreads faster and is much more difficult to control,” he said.
However, other researchers have attributed the lack of proper containment measures, not mutations, primarily to the resurrected outbreak.
“The reason this is widespread is that people aren’t doing enough,” said Kari Stefansson, founder and chief executive officer of deCODE Genetics, a leading Iceland-based genomic analysis company. “It seems like a very poor politics to blame the virus for deficiencies. They should choose someone of their own size, not this little virus.”
In one of the new studies, the British team of researchers had the advantage of not being shared with anyone else. They had access to a national database of the world’s largest coronavirus genome sequences. Researchers have gathered new evidence that the variants have taken over, at least in the United Kingdom, due to the fact that it spreads so fast.
“Looking at the cluster, the G variant grows faster,” said Eric M. Bolts, a researcher and research leader at the Global Infectious Disease Analysis Center of the Medical Research Council at Imperial College London. Stated.
Data collected by the Covid-19 Genomics UK Consortium allowed the team to observe the growth of infected clusters as a type of horse racing. Side by side, did clusters of 614G infections grow faster than infections involving ancestral variants?
Analysis shows that the 614G variant clearly won the race. The exact speed remains unknown, but the most likely value offers an exponential growth rate of 614G with an advantage of about 20%.
Catalina V. Koel, one of the researchers who is an associate professor of biology at Emory University, said, “This is exactly the kind of analysis that needs to be performed, and it supports G more contagious. “.
In another series of studies, a team led by Ralph Baric at the University of North Carolina tested the live virus and compared the 614G variant with its ancestral version. One found that the 614G virus was more infectious in samples of human bronchial and nasal tissues, the source of the virus most likely to infect others.
Another study published in Science found that mutants were more easily transmitted in hamsters when infected animals were within a few inches of each other. Scientists consider animal testing to be an important step in testing whether mutations that make the virus more infectious in laboratory dishes do so in living populations.
Dr. Barrick’s team placed the infected hamster in a cage adjacent to the cage of the uninfected hamster. The cages were a few inches apart, so the animals couldn’t touch each other. Any transmission can only occur in the air, droplets or aerosols.
Two days later, five of the eight hamsters with the 614G variant infected the pair. No one with the ancestral virus did.
“When we put all the data together, everything is consistent with a system that enhances infectivity and transmission,” said Dr. Barrick.
Viruses continue to change, and most of those changes are just typos, but some are more meaningful, Dr. Engeltaler said. “There could be additional changes that change the nature of the pandemic,” he said.
Already, Dr. Engeltaler has seen strong signs of such changes in his own unpublished data tracking the spread of various variants in Arizona.
“We need to listen to what the virus is telling us,” he said.
Muktita Suhartono contributed to the report.
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