A year-and-a-half on from the first cases in Wuhan, the origins of COVID-19 are still unknown.

Following the first cluster of infections at the Huanan wet market in China‘s Hubei province in late 2019, the most likely theory was that the coronavirus jumped from animals to humans.

But despite a World Health Organization (WHO) investigation into the origins of the pandemic earlier this year, experts do not appear to be any closer to a definite answer.

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What is the lab leak theory?

The lab leak theory is that the coronavirus may have accidentally escaped from a laboratory instead of jumping naturally from an animal – most likely a bat – to humans.

Those who support the idea believe it happened at the Wuhan Institute of Virology (WIV), where scientists have been studying bat-borne viruses since the SARS-CoV-1 outbreak in 2002, which killed 774 people worldwide.

Inside the lab, researchers experiment with live viruses in animals to decipher how susceptible humans might be to them.

All staff wear personal protective equipment (PPE) and there are strict protocols to avoid pathogens escaping.

But some people believe a basic human error could have resulted in the coronavirus escaping.

The WIV is just a few miles away from the Huanan wet market, where the first cases were detected, so they believe it could have spread there.

Most people who subscribe to the lab leak theory think it was an accident – not done on purpose by China as some conspiracy theorists claim.

What do we know so far?

An investigation into the origins of the pandemic was ordered by the WHO soon after the virus started spreading more widely in March 2020.

A team of WHO scientists were supposed to fly to Wuhan but were blocked by Chinese authorities.

They finally arrived in January 2021 – a year after the outbreak.

Their final report in March concluded that it was “likely to very likely” that the coronavirus jumped from a bat to a human via an unidentified animal species.

They determined that the virus escaping from a laboratory in Wuhan was “extremely unlikely”, but it was not completely ruled out.

The experts completely dismissed the idea the virus had been genetically engineered by humans.

During their 12-day visit, which saw them closely accompanied by Chinese officials everywhere they went, the scientists found records of badgers, porcupines, snakes, salamanders and crocodiles being sold at the Huanan wet market.

But they were unable to determine how the first cases emerged there.

“No firm conclusion therefore about the role of the Huanan market in the origin of the outbreak, or how the infection was introduced into the market, can currently be drawn,” the report said.

Why is it being taken seriously?

For months, the idea of a lab leak being behind the pandemic was considered a fringe or conspiracist theory.

But following the 2021 WHO report, some scientists have criticised the health authority for not taking it seriously enough.

Twenty-four researchers sent a letter to WHO saying its probe was not thorough and the lab leak scenario needed to be looked at again.

This week a classified US intelligence report was also leaked in the media, which suggested that three researchers at the WIV had to go to hospital for coronavirus-like symptoms in November 2019 – a month before the first cases were reported.

The report has given new weight to the lab leak argument, with US President Joe Biden then ordering American laboratories to launch a new investigation with a specific list of questions for the Chinese government.

“The United States will also keep working with like-minded partners around the world to press China to participate in a full, transparent, evidence-based international investigation and to provide access to all relevant data and evidence,” he said in a statement on Wednesday.

His press secretary Jen Psaki said the White House supported a new World Health Organization investigation in China, but that “would require China finally stepping up and allowing access needed to determine the origins”.

Dr Anthony Fauci, the US’s top infectious disease experts said of the lab leak theory on 11 May: “That possibility certainly exists, and I am totally in favour of a full investigation of whether that could have happened.”

Mr Biden’s Republican rivals, including former president Donald Trump, have long supported the lab leak theory and called for it to be looked at more closely.

The current president says the majority of the US intelligence community have “coalesced” around that scenario and a natural jump but “do not believe there is sufficient information to assess one to be more likely than the other”.

Other countries have also long insisted China may have covered up the origins of the pandemic and a lab leak is a viable argument, although they have no evidence for it.

In response to Mr Biden’s statement this week, China has accused the US of playing politics.

Foreign ministry spokesperson Zhao Lijian said it shows the US “doesn’t care about facts and truth, nor is it interested in serious scientific origin tracing”.

He claimed the US “wants to use the epidemic to engage in stigmatisation and political manipulation, and to shirk responsibility”.

“This is disrespectful to science and irresponsible to people’s lives, and moreover, it undermines the global unity of efforts to fight the epidemic,” Mr Zhao added.

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