Covid-19 pandemic hardly happened, new genetic dating study finds

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Researchers working to show when and how the virus first appeared in China calculate that it likely only infected the first human being in October 2019 at the earliest. And their models showed something else: It hardly was a pandemic virus.

“It was a perfect storm – we now know it took a chance or two to take hold,” said Michael Worobey, professor of evolutionary biology at the University of Arizona who worked on the study, at CNN.

“If things had been just a little different, if the first person who brought this to Huanan market decided not to go that day, or was even too sick to go and just stayed home. , that or any other early super-broadcast events may not have happened. We may never even have known.

The team used molecular dating, using the current mutation rate 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 had spread.

“Our study was designed to answer the question of how long could SARS-CoV-2 circulate in China before it was discovered,” said Joel Wertheim, associate professor in the Division of Infectious Diseases and of Global Public Health at the University of California, San Diego School of Medicine.

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“To answer this question, we have combined three important pieces of information: a detailed understanding of the spread of SARS-CoV-2 in Wuhan before the lockdown, the genetic diversity of the virus in China, and reports of the first cases of COVID-19 in China. By combining this disparate evidence, we were able to set an upper limit in mid-October 2019 for when SARS-CoV-2 started circulating in Hubei province. “

The evidence clearly indicates that the virus could not have circulated before this, the researchers said. There have been reports from Italy and other European countries that the virus may have infected people there before October. But Thursday’s study says just a dozen people were infected between October and December, Worobey said.

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“Given this, it is difficult to reconcile these low levels of the virus in China with allegations of infections in Europe and the United States at the same time,” Wertheim said in a statement. “I am quite skeptical of the COVID-19 allegations outside of China at this time.”

The study indicates that the virus appeared in China’s Hubei province and not elsewhere, the researchers said.

“Our results also refute claims of a large number of patients requiring hospitalization due to COVID-19 in Hubei province before December 2019,” they wrote.

From a handful of “sputum” cases at the end of 2019, the virus has exploded around the world. According to Johns Hopkins University, it has been diagnosed in 121.7 million people and has killed nearly 2.7 million people. The United States has been by far the most affected country, with nearly 30 million cases diagnosed and nearly 540,000 deaths.

The study does not show which animal caused the virus. Genetic evidence shows that bats carry a closely related virus and also suggests that another intermediate animal species may have been infected and transmitted the virus to a human somewhere.

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It happens. The United States Centers for Disease Control and Prevention regularly tracks and reports cases of new strains of influenza infecting people who attend county fairs and interact with pigs, for example. But so far none of these infections have resulted in an epidemic or even an epidemic.

What is needed is an infected person and a lot of contact with other people – like in a very dense seafood market. “If the virus is not lucky enough to find these circumstances, even a well-adapted virus can go away,” Worobey said.

“It gives you some perspective – these events probably happen a lot more frequently than we think. They just don’t succeed and we never hear about them,” Worobey said.

And that could have happened with Covid-19.

In the models run by the team, the virus only takes off about 30% of the time. The rest of the time, models show it should have died out after infecting a handful of people.

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“What may have happened here is that the virus was spreading to a very small number of people in October, November and December, and then it entered this Huanan seafood market,” he said. declared Worobey.

It is likely that the market was not where the virus first infected people, but just where it grew.

Considering how little time the virus has spent, it’s remarkable that it was identified so quickly, Worobey said.

“It was quite clearly some time in December before there was a large enough group of people infected that there was a chance of discovering a new virus,” he said. In January 2020, it had been sequenced and characterized.

Nonetheless, it was too late – perhaps because Covid-19 isn’t deadly enough. The first SARS virus killed nearly 10% of its victims between 2002 and 2004 before being stopped thanks to a concerted global effort.

“As a scientific community, we were certainly aware of the pandemic potential of a highly transmissible, moderately virulent pathogen. But our disease notification system depends on detecting peaks in hospitalizations and deaths. Obviously, this was not enough to stop Covid-19. Wertheim told CNN.

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