A new genetic analysis of the virus that causes Covid-19 taken from more than 7,600 patients around the world shows the virus has been circulating in people since late last year, and must have spread extremely quickly after the first infection.
Researchers in Britain looked at mutations in the virus and found evidence of rapid spreading, but no evidence the virus is becoming more easily transmitted or more likely to cause serious disease.
“The virus is changing, but this in itself does not mean it’s getting worse,” genetics researcher Francois Balloux of the University College London Genetics Institute told CNN.
Balloux and colleagues pulled viral sequences from a giant global database that scientists around the world are using to share data. They looked at samples taken at different times and from different places, and said they indicate that the virus first started infecting people at the end of last year.
“This rules out any scenario that assumes SARSCoV-2 may have been in circulation long before it was identified, and hence have already infected large proportions of the population,” Balloux’s team wrote in their report, published in the journal Infection, Genetics and Evolution.
“Our results are in line with previous estimates and point to all sequences sharing a common ancestor towards the end of 2019, supporting this as the period when SARS-CoV-2 jumped into its human host,” the team wrote in the report, published Tuesday.
“It’s very recent,” Balloux said. “We are really, really, really confident that the host jump happened late last year.”
They also found genetic evidence that supports suspicions the virus was infecting people in Europe, the US and elsewhere weeks or even months before the first official cases were reported in January and February.
Balloux’s team had their findings reviewed by other experts, a process called peer review, before they were published in the journal. He said some reports by other teams, published online in on what are called pre-print websites, may have drawn incorrect conclusions.
“All viruses naturally mutate. Mutations in themselves are not a bad thing and there is nothing to suggest SARS-CoV-2 is mutating faster or slower than expected. So far we cannot say whether SARS-CoV-2 is becoming more or less lethal and contagious,” Balloux said.
