WASHINGTON - President Joe Biden on Wednesday (May 26) directed US intelligence agencies to further investigate the origins of the Covid-19 virus, which will include addressing whether the coronavirus emerged in China from human contact with an infected animal or from a lab accident.

No definitive conclusion has been reached, and the intelligence community does not believe it has sufficient information to favour one scenario over the other, Mr Biden said in a statement.

He added that the officials are due to report back in 90 days and have been asked to draw up specific queries for China, among other areas of further inquiry.

In explaining its calls for further investigation, the Biden administration has said that getting to the bottom of the origin of the coronavirus pandemic will help America and the world understand how to prepare for the next pandemic.

Questions on the origins of the virus centre on whether the virus emerged naturally or was bioengineered, and separately, whether it was leaked from a laboratory - specifically, the Wuhan Institute of Virology in China.

Beijing flat out rejects the possibility of a laboratory leak and calls it an effort by Washington to spread disinformation.

Once dismissed outright as a conspiracy theory, the idea that the Covid-19 virus could have emerged from the Wuhan laboratory has gained momentum in the US in recent days, even though most scientists still favour natural causes. Some have criticised media reports for fostering a false equivalence between natural causes and lab leak theories.

Mr Biden's statement was notable for its refusal to rule out the possibility that the virus was leaked from a lab.

What lies behind Washington's increased willingness to consider what has been called the "lab leak theory"?

One factor is the continued lack of conclusive proof either way, fuelled by recent reports with circumstantial evidence that have kept the lab leak possibility alive, said analysts.

"There's no conclusive proof one way or the other where the virus came from," Eurasia Group US managing director Jon Lieber told The Straits Times (ST). "The reality is we just don't have enough evidence one way or the other to say what happened in the lab."

Although a joint report by the World Health Organisation (WHO) and China scientists in March dismissed a laboratory accident as "extremely unlikely" while deeming animal-to-human transmission "likely to very likely", it was criticised - including by the US - for being insufficiently independent and having limited access to certain data.

On May 14, the prestigious journal Science published a letter from 18 scientists that criticised the WHO-China joint study for not giving both theories balanced consideration, and called for a more rigorous and transparent investigation.

"Yet more investigation is still needed to determine the origin of the pandemic. Theories of accidental release from a lab and zoonotic spillover both remain viable," they wrote.

On top of that, The Wall Street Journal reported on May 24 that US intelligence found that three researchers from the Wuhan lab sought hospital care after becoming ill in November 2019.

"There's been new attention brought to the lab leak hypothesis," University of Minnesota Duluth's College of Liberal Arts dean Jeremy Youde said, citing the Science journal letter.

"While the evidence for that still strikes me as circumstantial at best, ignoring it would likely make the administration's opponents allege that Biden and the World Health Organisation were trying to hide something," the global health politics researcher told ST.

Domestic politics in America also marred the initial consideration of the lab leak theory, given that former president Donald Trump had been on course to win re-election before the pandemic struck in early 2020.

His administration's championing of the theory was viewed as an attempt to deflect attention from his poor handling of the pandemic, which lowered its credibility.

"The issue was massively, massively politicised. The Trump administration used it to go on the offensive against China, and opponents of the Trump administration, including many in the media, dismissed it as a result of that," said Mr Lieber.

But now that the issue is less politically charged, Democrats and Republicans are more aligned on confronting China, he said.

"Biden can more credibly call out China and say that there should at least be an investigation to this question," Mr Lieber added.

The Biden administration's calls for further investigation is also a way of calling the Chinese government to account, amid the ongoing superpower rivalry.

"If China is not willing to be transparent or be forthcoming with information to the WHO, that will likely be used to bolster the US' geopolitical standing - arguing that it is on the side of openness and getting to the bottom of the pandemic while China obfuscates," said Dr Youde.

Mr Biden's call for further investigation also helps to reassert American leadership in global health, he added. The administration has framed getting to the bottom of this pandemic's source as a way to prepare for the next one.

"After the Trump administration's refusal to engage the global health community, the Biden administration has sought to take a more active leading role. This could be a way to show that the US' action matches its rhetoric," said Dr Youde.

While America is trying to score points at China's expense to some extent, that does not negate its concerns, said analysts.

"That's true to an extent. But it's also a legitimate question," said Mr Lieber. "It does help the political narrative against China. But more fundamentally, it's something that the US and the world needs to know the answer to."

Mr Biden has also not prejudged the outcome and simply called for a rigorous investigation in alignment with WHO, unlike Mr Trump who jumped to conclusions for predominantly political reasons, Georgetown University global health law professor Lawrence Gostin told ST.

"There is certainly a political dimension to President Biden's insistence on closer scrutiny of the Wuhan Institute laboratory. Yet, I view his statement as a clear and convincing call on the international community to investigate the origins of Sars-CoV-2," said Professor Gostin.

"Given considerable circumstantial evidence of a lab leak, it warrants a full and fair inquiry," he added.