Since the early days of the COVID-19 pandemic, two main theories have circulated about its origin.
Many scientists believe that SARS-CoV-2 - like other viruses belonging to the beta-coronaviruses family - has a natural origin and was transmitted from bats to people, likely via an unknown intermediary.
This theory was widely accepted at the start of the pandemic, and
But recently, a second theory - that the virus leaked from a laboratory - has gained traction, despite no new scientific evidence emerging. The WHO team had previously concluded such a scenario was “extremely unlikely”.
There is much at stake when it comes to pinpointing the source of the outbreak - in addition to helping prevent future pandemics, discovering the origin of COVID-19 could also have a major impact on international relations.
“We don’t have the full jigsaw yet," says University of Queensland virologist Ian Mackay.
The natural emergence theory
Professor Dominic Dwyer, the NSW director of public health pathology, travelled to the Chinese city of Wuhan as part of a World Health Organization delegation in January.
Tasked with investigating the cause of the pandemic, he says there were two main parts to their mission.
“One was to try and review what had actually happened based on the evidence we were given, and to see, based on that evidence, what would be the most to the least likely of the various hypotheses,” he told SBS News.
“The second part is then to say, what further work needs to be done to solve this? You can’t do this work in four weeks - this is something that could take years, based on our experience of other diseases.”
Following the delayed visit, , the WHO team concluded the most likely scenario was the virus jumped from bats into humans via an intermediate animal - a process known as “zoonosis”.
Professor Dwyer inspects the Huanan wet market in Wuhan. Source: Supplied
History tells us this is a “tried and true process,” Professor Dwyer says.
“Plenty of other viruses have gone down this pathway before, including the original SARS and MERS, which are coronaviruses that have come across into humans,” he said.
“Nearly all human viruses identified in the last 40 or 50 years have come from animals in one form or another, and bats are a major contributor. So, there’s a history there and it’s well documented.”
Professor Mackay said there is substantial evidence of “natural spillovers” due to farming practices and other ways humans are exposed the viruses carried by animals.
“We have lots of evidence that spillovers happen like this all the time. Most of the time, they probably happen and don’t go any further - they’re the end of that transmission chain,” he told SBS News.
“This time, it wasn’t the case - like it wasn’t the case when when SARS took off.”
Chinese authorities reported many of the first cases of COVID-19 occurred in a wet market in Wuhan.
Marion Koopmans and Peter Ben Embarek of the WHO team farewell their Chinese counterpart Liang Wannianin in Wuhan, China, 9 February 2021. Source: AAP
Wuhan is also home to the Wuhan Institute of Virology, a Chinese government-backed lab with expertise in coronavirus research.
“A wet market scenario - where you have animals that are potentially infected by bats under enormous stress in cages, and there’s a lot of people around often in crowded locations - is a perfect recipe for an outbreak,” Professor Dwyer said.
While researchers have some leads supporting this theory, researchers are yet to pinpoint the animal intermediary responsible for transferring the virus to humans.
“Well, no animal has been identified, but then we hadn't found the animal that was the original source of SARS for quite some time. It took a while to get there. That's just a matter of sampling a lot of animals, doing a lot of that work,” Professor Mackay said.
The laboratory leak theory
On Sunday, world leaders attending the G7 summit released a communique calling for a "transparent, expert-led and science-based" phase two COVID-19 origin study to be convened by the WHO in China.
It followed US President Joe Biden's order last month for national intelligence agencies to “redouble” their efforts to investigate the virus's origins, including "whether it emerged from human contact with an infected animal or from a laboratory accident”.
"As of today, the US intelligence community has coalesced around two likely scenarios but has not reached a definitive conclusion on this question," he said.
Speaking to reporters at the G7 summit, Mr Biden said transparency mattered.
"Transparency matters across the board. And I think the idea that, for example, one of the things I raised - and others raised, I wasn't the only one who raised this piece of it - is that we don't know," he said.
"We haven't had access to the laboratories to determine whether or not - I've not reached a conclusion because our intelligence community is not certain whether or not this was a consequence of a - [from] the marketplace, of bat interfacing with animals in the environment that caused this... or whether it was an experiment gone awry in laboratory."
Mr Biden’s comments appear to also signal a diplomatic escalation of the issue, with the United States using the COVID-19 investigation to exert pressure on China as tensions between the countries rise.
They also followed reports, citing US intelligence, that three researchers from the Wuhan institute were hospitalised with a flu-like illness in November 2019, one month before China reported the first COVID-19 case.
John Lee, a senior fellow at the US Studies Centre, said “circumstantial evidence” for the lab leak theory has existed from the start, but was quickly dismissed by parts of the US government and by the media.
“One of the reasons why is because it was the preferred explanation of former president Donald Trump,” he told SBS News.
“That shouldn’t have a bearing on how credible or not credible the theory is, but it has been politicised - initially by Donald Trump, and also by those who didn’t like Donald Trump.”
Mr Lee said Mr Biden’s order is “recognition that we don’t know the source but both those theories have credible aspects to them that need to be investigated”.
‘You need evidence to take the science further’
Proponents of the lab leak theory have raised a number of sometimes-spurious arguments.
These include that the specific source has not yet been identified, and that the virus was first detected in Wuhan - the same city where the institute of virology is also located.
The difficulty with this theory, Professor Dwyer says, is that there is very little firm evidence.
“There have been suggestions about a whole range of different scenarios, including a deliberate or accidental leak, but the trouble with that is you have to be able to unpack that,” he said.
“You need evidence to take the science further.”
He said one flaw in the theory is there is no evidence of COVID-19 at the Wuhan institute before the pandemic.
“If you have a lab leak, you would have to have had the virus in the lab, and nobody has discussed that. Laboratories like the one in Wuhan, and others around the world, publish papers on these viruses as quickly as they can - that’s part of the scientific process.”
Some researchers have been investigating whether a particular genetic feature of COVID-19 suggested it was bioengineered.
Professor Dwyer said this wasn't the case.
“It’s actually present in other coronaviruses as well, including MERS,” he said.
Professor Mackay agreed that similar genetic features were already present in other viruses.
“Again, it’s probably a case of us not sampling enough of these viruses yet,” he said.
As for the location of the institute in Wuhan, Professor Mackay cautioned drawing simple conclusions.
"It could just be where that lab is, studying the things that are most relevant,” he said.
People run along the banks of the Yangtze River in Wuhan on 11 January, as the city marks the first anniversary of China confirming its first COVID-19 death. Source: Getty Images
What now?
Right now, there is no definitive conclusion and both theories remain on the table.
“I think we have to keep an open mind until we have more evidence than we do now,” Professor Mackay said.
“You don't exclude these ideas, but you want to try and understand how they might arise and whether in the process of arising like that, that it makes sense,” Professor Dwyer added.
“The damage with all of this is it stops cooperation and collaboration - that’s how you solve scientific problems. And it can take time.”
A group of scientists have also joined calls for further investigation, penning a letter published in the journal Science last month.
"[M]ore investigation is still needed to determine the origin of the pandemic. Theories of accidental release from a lab and zoonotic spillover both remain viable. Knowing how COVID-19 emerged is critical for informing global strategies to mitigate the risk of future outbreaks," the letter said.
Mr Lee believes further open, transparent investigation is unlikely - “simply because it won’t be allowed by China”.
“What I think will happen then is the circumstantial evidence will increasingly be put out there. The battle going on now is really about who carries the burden of proof - Beijing or outside entities?”
