Since the start of the SARS-CoV-2 pandemic, researchers have been trying to work out where the virus originated and how it spread.
From a scientific and public healthcare perspective, the idea is for authorities to use the information to prepare for the next time a new virus emerges and spreads internationally, creating the threat of another pandemic.
Take the example of the emerging cases of avian influenza in Southeast Asia. There are significant fears among health experts that that virus could eventually mutate and spread from birds or other non-human animals to humans. Luckily, that hasn't happened so far.
In the case of COVID-19, however, there is also an element of politics in the search for the origins of the virus.
Two US authorities back the lab leak theory
From early on in the pandemic, some officials have suggested that SARS-CoV-2 escaped or was leaked, either by accident or intentionally, from a laboratory in Wuhan, China. The virus was first detected among people in Wuhan.
There is a competing idea that the virus spread in the community more naturally, via live and infected animals to humans at a market in Wuhan.
The debate went quiet for a while but resurfaced in late February 2023 when the Wall Street Journal reported that the US Department of Energy had changed its position and that it now supported the lab leak theory.
Cristopher Wray, the director of the U.S. Federal Bureau of Investigation (FBI) then also publicly endorsed the theory in an interview on Fox News.
"The FBI has for quite some time now assessed that the origins of the pandemic are most likely a potential lab incident in Wuhan," Wray told Fox News on February 28.
China has dismissed the claims since the start of the pandemic. Responding to the US in late February, China reasserted its theory that the coronavirus most likely developed in animals in the wild, mutated, and then jumped to infect humans.
Mao Ming, China's Foreign Ministry spokesperson, urged the US "to respect science and facts," and "stop turning origin tracing into something about politics."
Moderate-to-low confidence in the lab leak theory
Experts viewed the updated assessment from the Department of Energy in February as significant because the department oversees a network of laboratories US, including some which do advanced biological research.
But there were also significant caveats.
First, the Department of Energy did not say why, or on what scientific basis, it changed its position.
Second, it ranked its own confidence in the lab leak theory as "low."
The FBI, meanwhile, ranked its confidence in the theory as "moderate."
Third, four other US departments, including the country's national intelligence panel, maintained their positions that the virus spread via a natural transmission from animals to humans.
Fourth, two further US departments remained undecided.
And fifth, US President Joe Biden declined to make his position public.
Is the lab leak theory a conspiracy?
The lab leak theory contains at least two other theories.
One is that the virus was leaked from a lab by accident due to substandard security measures — that's the idea that is escaped.
The other is that the virus was developed and released on purpose as a form of biological weapon.
Early in the pandemic, a prominent Indian politician tweeted their claim that the coronavirus was a weapon that "went rouge" and that is was an act of terror. The tweeter, Manish Tewari, probably misspelt "rogue".
But even US intelligence officials have debunked Tewari's and similar claims that China created SARS-CoV-2 as a biological weapon.
A report by the US Office of the Director of National Intelligence (ODNI) said in 2021 that Chinese officials had had no foreknowledge of the virus before the outbreak occurred.
While the report said that the Wuhan Institute of Virology, the lab in question, had "previously created chimeras, or combinations, of SARS-like coronaviruses, [...] this information does not provide insight into whether SARS CoV-2 was genetically engineered by the [institute]."
The zoonotic theory: COVID-19 "most likely" originated in nature
A number of scientists who have studied the origins of the COVID-19 pandemic continue to refute the claim that the coronavirus originated in a laboratory.
They point to evidence published in several high-profile scientific journals that the 2019 novel coronavirus originated in nature and passed from animals to humans.
Investigations suggest that a Wuhan market, where live animals were sold, is likely to have been the epicenter of the pandemic.
The World Health Organization undertook a first phase investigation into the origins of COVID-19 and filed a report in 2021.
Their preliminary conclusions supported the zoonotic theory, suggesting the virus had emerged and spread naturally.
In February 2023, it was reported by the journal Nature that the WHO had "quietly shelved" plans for the second phase of its investigation. But the WHO said itself that it would do everything possible "until we get the answer" on COVID's origins.
Many scientists say we still lack genuine proof for any theory of COVID-19's origins. The zoonotic theory has the most robust evidence, yet three years on, there's still little evidence of a direct ancestor of the virus in nature.
If researchers ever find an ancestor to the virus, it would help discount the idea that SARS-CoV-2 had come out of nowhere or, indeed, a lab in Wuhan.
Edited by: Zulfikar Abbany