“It was a perfect storm – we now know that she had to take a stroke of luck or two to really settle down,” Michael Worobey, a professor of evolutionary biology at the University of Arizona who worked on the study, told CNN.
“If things had been a little bit different, if that first person who brought this to the Huanan market had decided not to go that day, or even was too sick to go and just stayed home, this or another early super-spreading event may not have occurred. We may never have known about it. “
The team employed molecular dating, using the rate of mutations in progress to calculate how long the virus has been around. They also ran computer models to show when and how it could have spread and how it spread.
“Our study was designed to answer the question of how long SARS-CoV-2 may have been circulating in China before it was discovered,” said Joel Wertheim, associate professor in the Division of Infectious Diseases and Global Public Health, University of California, School of Medicine of San Diego.
“To answer this question, we combined three important pieces of information: a detailed understanding of how SARS-CoV-2 spread in Wuhan before the blockade, the genetic diversity of the virus in China and reports of the first cases of COVID-19 in China. By combining these disparate lines of evidence, we were able to establish a ceiling from mid-October 2019 to when SARS-CoV-2 started to circulate in Hubei province. “
The evidence strongly indicates that the virus could not have circulated before that, the researchers said. There have been reports in Italy and other European countries of evidence that the virus may have infected people there before October. But Thursday’s study indicates that only about a dozen people were infected between October and December, Worobey said.
“Given this, it is difficult to reconcile these low levels of viruses in China with allegations of infections in Europe and the United States at the same time,” said Wertheim in a statement. “I am quite skeptical of COVID-19’s claims outside of China at that time.”
The study indicates that the virus appeared in the Chinese province of Hubei and not elsewhere, the researchers said.
“Our results also refute the claims of a large number of patients who needed hospitalization due to COVID-19 in Hubei province before December 2019,” they wrote.
The study does not show which animal was the source of the virus. Genetic evidence shows that bats carry a closely related virus and also suggests that another intermediate species of animal was probably infected and transmitted the virus to a human somewhere.
What is needed is an infected person and a lot of contact with other people – as in a crowded seafood market. “If the virus is not fortunate enough to meet these circumstances, even a well-adapted virus can disappear,” said Worobey.
“It gives you some perspective – these events are probably happening a lot more often than we think. They just don’t happen and we’ve never heard of them,” said Worobey.
And that could have happened with Covid-19.
In the models that the team ran, the virus only takes off about 30% of the time. The rest of the time, the models show that it should have been extinguished after infecting a handful of people.
“What may have happened here is that the virus was spreading to a very low number of people in October, November and December and then entered this seafood market in Huanan,” said Worobey.
It is likely that the market was not where the virus first infected people, but only where it was amplified.
Given how little time the virus has existed, it is notable that it was identified so quickly, Worobey said.
“It passed very clearly in December before there was a large enough group of people infected that there was a chance to discover a new virus,” he said. In January 2020, it was sequenced and featured.
However, it was too late – perhaps because Covid-19 is not deadly enough. The first SARS virus killed about 10% of its victims from 2002 to 2004, before being stopped by a joint global effort.
“As a scientific community, we were certainly aware of the pandemic potential of a highly transmissible and moderately virulent pathogen. But our disease reporting system depends on detecting peaks in hospitalizations and deaths. Obviously, that was not enough to stop Covid-19.” , Wertheim told CNN.