The rapid coronavirus spread started last year, according to a new genetic analysis of the virus. Scientists found evidence after studying viral sequences.
They investigated mutations in the virus and detected evidence of quick spread. However, there is no evidence the virus goes through easier transmission or that it is 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 looked into viral sequences from a global database that scientists use to share data. They examined samples taken at different times and from different locations.
Published in Infection, Genetics and Evolution, findings revealed that the virus first began infecting people at the end of 2019.
"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.
Some doctors assumed the virus was spreading for several months and may have invisible infected many more people than reported. This situation would have suggested that there might be some immunity developed in some populations.
"Everyone was hoping for that. I was too," Balloux said.
He estimated that at the most, 10% of the global population had exposure to the virus already.
Infection from a bat
Several studies revealed that the new coronavirus, known as SARS-CoV-2, started in a bat. However, it had to have transmitted to another animal before it transferred to humans. The first human cases sprang in Wuhan, China, in December last year.
"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," Balloux's team wrote.
"It's very recent," Balloux said. "We are really, really, really confident that the host jump happened late last year."
"It has been introduced and introduced and introduced in almost all countries," he added.
The researchers discovered genetic evidence that backs beliefs that the virus was infecting people in Europe, the US and elsewhere weeks or even months before the first official report of cases in January and February.
However, Balloux stressed it will be impossible to find the "first" patient in any country.
"All these ideas about trying to find a Patient Zero are pointless because there are so many patient zeros," he said.
Experts already reviewed the findings of the analysis before it was published in the journal. Some studies posted on pre-print websites may have 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.
More studies
Meanwhile, Lane Warmbrod, an analyst at the Johns Hopkins Center for Health Security, said there should be more studies in animals to trace how changes in the genetics of the virus could make it more or less infectious or pathogenic.
"Just because these studies tell us these mutations are quickly spreading or becoming dominant doesn't mean anything except we know it happened. It doesn't actually tell us anything about what's happening biologically," Warmbrod told CNN.
