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It is considered likely that Sars-CoV-2 jumped to humans at a wild animal market in Wuhan.
Photo: Nicolas Asfouri / AFP
Where did Sars-CoV-2 come from?
This question has been the subject of intensive scientific debate for more than two years.
Two new studies published in the journal Science clearly point in one direction: the starting point of the corona pandemic was not a laboratory, but a wild animal market in Wuhan, China.
The thesis that the virus could have come into the world from a safety laboratory has been invalidated.
The investigations have shown "that it is simply not plausible that this virus was introduced to the Wuhan market in any way other than through the wild animal trade," said one of the scientists involved, virologist Michael Worobey from the University of Arizona .
Just because something is possible doesn't make it probable
Last year, Worobey signed an open letter calling for the theory of a laboratory accident at the Institute of Virology in Wuhan to be further examined.
The knowledge gained since then would have made him rethink, the virologist said.
The virus “emerged on this market and spread from there.”
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Kristian Andersen from the Scripps Research Institute, who was also involved in the work as a professor of immunology and microbiology, said: The theory of a laboratory leak was not refuted with the new publications.
But it is important to understand “that there are possible and probable scenarios.
And that possible is not the same as probable.«
The preprints of the studies, i.e. a version that has not yet been checked by independent experts, were published in February.
The first Covid cases are distributed geographically around the wildlife market
The first study analyzed the geographical distribution of the first Covid cases in December 2019.
The pattern showed that the cases were tightly clustered around the Huanan Wildlife Market in Wuhan.
Some of the first patients who had not recently visited the market lived in the immediate vicinity of the market.
Within the market, the experts found clusters of cases.
This accumulation is "very, very specific" in parts of the market where wild animals such as raccoon dogs were sold.
These animals are possible carriers of coronaviruses.
It is statistically extremely unlikely that the pattern that resulted in the location of the cases could have arisen by chance.
For the second study, the researchers carried out a genome analysis of the virus that was detected in the first corona patients.
They examined two tuning lines of the pathogen.
They concluded that both jumped from animals in the market to humans in separate events - in November and December 2019.
A so-called spillover event may even have occurred twice.
It is unlikely that the virus circulated in humans before November 2019, the scientists wrote.
But isn't it unlikely that what is actually a one-off event will occur twice within a very short space of time?
Joel Wertheim, co-author of the study and an expert in viral evolution at the University of California, San Diego, said: The conditions are special, but they were there - for example, that people and animals lived in close proximity and that the virus originated from animals people, but can also be transmitted from person to person.
"The barriers to spread were lowered to the point where we thought multiple introductions were to be expected," Wertheim said.
The laboratory thesis persists
Shortly after the outbreak of the corona pandemic at the end of 2019, speculation began as to where it started.
There has been debate as to whether the virus may have escaped in an accident at the Institute of Virology in Wuhan.
Among other things, research is carried out there on corona viruses.
The Chinese government vehemently denied this thesis.
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In January 2021, an international research team from the World Health Organization (WHO) was able to travel to Wuhan.
However, its report did not provide any clear results on the origin of the pandemic.
At the time, the WHO experts classified the so-called laboratory theory as “extremely unlikely”.
However, doubts and criticism quickly arose about the report and the investigation itself.
Many countries have expressed concern that international experts have been denied access to important data in their investigation in China.
The Chinese government has so far rejected further investigations, as requested by WHO chief Tedros Adhanom Ghebreyesus.
The new studies are also not definitive proof for or against any of the theories about the origin of the virus.
But for many experts, the results are quite clear.
"These two studies provide really compelling evidence for the natural origin hypothesis," said University of Minnesota veterinary medicine researcher Matthew Aliota, who was not involved in either study.
Since it is impossible to take samples from an animal that has been at the market, "this is perhaps the best evidence one can get".
There may never be definitive proof
The wholesale market in Wuhan, where live animals were sold, among other things, was suspected early on as the place of origin of the pandemic.
At the end of December 2019, several people who worked at the market fell ill with a new type of pneumonia.
At the end of December it became clear that a new corona virus was responsible for the mysterious diseases.
The Chinese authorities then ordered the Wuhan market to be closed.
On January 1, 2020, the police closed the wildlife market, the stalls in the market were washed and disinfected.
According to Chinese researchers, the virus was later found in numerous samples from surfaces and sewers on the market.
Clear evidence cannot be provided by swabs from infected animals on the market.
vki/AFP/AP