Covid-19 origin: Why the Wuhan lab-leak theory must formally be investigated
A year and a half into the pandemic, we still do not know exactly where the SARS-CoV-2 virus, which causes Covid-19, came from. The prevailing view so far has been that the virus "spilled over" from bats into humans.
But there are increasing calls to investigate the possibility that it emerged from a lab in Wuhan, China, where Covid first appeared at the end of 2019.
We know the sequence of the SARS-CoV-2 virus is close to that of bat coronaviruses. Several decades ago its "ancestor" was circulating in bat populations in southern Asia. But there are still many unanswered questions: we don't know how the virus arrived in Wuhan, how its sequence evolved to allow human infection, and under what conditions it infected the first people who crossed its path. And for each of these stages, we don't know whether there was a human contribution (direct or indirect).
Zoonotic transmission pathways, in other words the passage of viruses from animals to humans, are now widely documented around the world. Scientists even consider that this is a principal mechanism for the spreading of new viruses.
But the fact that the pandemic began in the vicinity of a main virus research centre that specialises in the study of coronaviruses with epidemic potential in humans - the Wuhan Institute of Virology - has given rise to another hypothesis, the lab leak theory. Lab accidents have already led to human infections, including the H1N1 flu pandemic of 1977, which killed more than 700,000 people.
Which theory is correct? In the absence of definitive proof, and without promoting conspiracy theories, there needs to be a serious international conversation about the origin of SARS-CoV-2.
In the scientific community, the debate on the origin of SARS-CoV-2 started with the publication of two articles at the very beginning of the outbreak.
The first, dated February 19, 2020, was published in the medical science journal The Lancet. This article, signed by 27 scientists, highlighted the efforts of Chinese experts to identify the source of the pandemic and share the results.
The authors deplored "rumours and misinformation" about the origins of the virus, and stated that they "strongly condemn conspiracy theories suggesting that Covid-19 does not have a natural origin".
The authors based their opinion on the first published sequence data, but did not detail the scientific arguments supporting a natural origin.
In March 2020, another article published in Nature Medicine provided a series of scientific arguments in favour of a natural origin. The authors argued:
The natural hypothesis is plausible, as it is the usual mechanism of emergence of coronaviruses
The sequence of SARS-CoV-2 is too distantly related from other known coronaviruses to envisage the manufacture of a new virus from available sequences Its sequence does not show evidence of genetic manipulation in the laboratory.
This last argument can be questioned, as methods do exist which allow scientists to modify viral sequences without leaving a trace.
These include cutting the genome into fragments that can later be joined together or, more recently, using the ISA protocol, whereby overlapping fragments naturally come together in cells through homologous recombination: a phenomenon in which two DNA molecules exchange fragments. Besides, genetic manipulation is not the only scenario compatible with a laboratory accident or leak.
Meanwhile, intense research that has been carried out for more than a year to try to prove the zoonotic scenario has not been successful so far: all 80,000 animal samples, from some 30 species, have tested negative. The samples came from farm animals and wild animals from different provinces in China. But it is important to note that this large number of negative samples does not refute the zoonotic scenario.
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