New genetic analysis of the virus responsible for COVID-19, taken from more than 7,600 patients worldwide, shows that it has been circulating in humans since the end of last year and must spread extremely quickly after the first infection.
British researchers have examined mutations in the virus and found evidence of rapid spread, but no evidence that the virus is more easily transmitted or no longer causes serious illness.
“The virus is changing, but that does not mean that it is getting worse,” genetic researcher François Balloux of the University College London Genetics Institute told CNN.
Balloux and his colleagues have extracted viral sequences from a giant global database that scientists around the world use to share data. They looked at samples taken at different times and in different places, and said they indicated that the virus had started infecting people late last year.
“This excludes any scenario which assumes that SARSCoV-2 could have been in circulation long before it was identified, and therefore have already infected a large part of the population,” wrote the Balloux team in its report, published in the journal Infection, Genetics and Evolution.
This is bad news. Some doctors hoped that the virus had been circulating for many months and could have quietly infected many more people than had been reported. This would give hope that there might be already established immunity in certain populations.
“Everyone was hoping for that. Me too, said Balloux.
Their results pour cold water on such an idea. Up to 10% of the world’s population has been exposed to the virus, Balloux said.
Between humans and bats
Many different studies have shown that the new coronavirus, often called SARS-CoV-2 by scientists, came from a bat, but had to infect another animal before it jumped into humans. The first human cases were reported in Wuhan, China, last December.
Viruses make mistakes every time they reproduce, and these mutations can be used as what is known as a molecular clock to track a virus over time and geography.
“Our results are in line with previous estimates and indicate that all sequences share a common ancestor in late 2019, supporting this as the period when SARS-CoV-2 jumped into its human host,” the team wrote.
“This is very recent,” said Balloux. “We are really, really, really confident that the host jump happened at the end of last year. “
Indeed, viral samples from around the world show multiple mutations, and they are similar mutations. “Everything is everywhere,” the team wrote.
“It has been introduced and introduced and introduced in almost all countries,” added Balloux.
They also found genetic evidence to support suspicions that the virus was infecting people in Europe, the United States and elsewhere weeks, even months before the first official cases were reported in January and February. It will be impossible to find the “first” patient in any country, said Balloux.
“All of these ideas about finding a Patient Zero are useless because there are so many patient zeros,” he said.
The results of the Balloux team were reviewed by other experts, a process called peer review, before being published in the journal. He said some reports from other teams, published online on so-called preprinted websites, may have drawn incorrect conclusions.
“All viruses mutate naturally. The mutations themselves are not a bad thing and there is no evidence to suggest that SARS-CoV-2 mutates faster or slower than expected. So far, we cannot say whether SARS-CoV-2 is becoming more or less deadly and contagious, “said Balloux.
Lane Warmbrod, analyst at the Johns Hopkins Center for Health Security, who follows reports on the genetics of the new coronavirus. She said more studies are needed in animals to demonstrate how changes in the virus’s genetics could make it more or less infectious or pathogenic.
“Just because these studies tell us that these mutations spread quickly or become dominant doesn’t mean that we know it happened. It actually doesn’t tell us anything about what’s going on biologically, ”Warmbrod told CNN.
Mutation reports can be important for teams working on drugs and vaccines to fight the coronavirus. Vaccines, in particular, must target the parts of the virus that are retained – which do not change much over time.
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