Top scientists who dismissed the theory that Covid leaked from a lab later admitted that it may be possible, newly released messages have revealed.

In a highly influential paper published in March 2020, the team of leading US virologists said 'we do not believe that any type of laboratory-based scenario is plausible'.

Instead, the report – which featured in the reputable journal Nature Medicine – suggested that the pandemic may have been caused by an animal spillover event, which is when a disease jumps from animals to humans.

But private messages released by US senator Rand Paul and published by Homeland Security appear to show that the researchers doubted these assertions as early as July 2020.

The scientists also raised concerns that the Wuhan Institute of Virology (WIV) – eight miles from where Covid emerged – had been carrying out experiments on coronaviruses without strict safety measures.

The new documents show that one of the study's lead authors, Kristian Andersen, of the Scripps Institute in California, had doubts around three months after their work was published.

On the messaging platform Slack, he wrote: 'At the end of the day, we really don't have any hard evidence one way or the other – and especially given some of the recent evidence, we also can't rule out that somebody actually put it in there.

'That's obviously not to say that somebody *did*, but we can't rule it out. Our paper was pretty strong in saying there's no way, but I have less confidence in that statement at this stage.'

The theory that Covid may have leaked from a lab emerged in the early months of the pandemic but was widely dismissed at the time as a conspiracy theory. 

Supporters of the belief argue the virus may have accidentally or otherwise escaped from the Wuhan virology institute, which is located around eight miles from the wet market where the outbreak was first detected.

US President Donald Trump claimed in May 2020 he had seen evidence that the virus, which killed at least seven million people across the world, came from a lab.

And it was brought up again in February 2023 when former FBI director Christopher Wray said that it had 'most likely' originated in a 'Chinese government-controlled lab'.

China rejected the allegation, accusing the United States of 'political manipulation'. 

Viscount Ridley, the author of Viral: The Search for the Origin of Covid-19, told The Telegraph today: 'These messages confirm that the authors continued to believe a lab leak was possible.

'So why did they not correct or retract the paper that misled the world?'

At the time, the paper also argued that research into bat coronaviruses – the group of viruses from which it is believed Covid may have originated – had been going on 'across the world'.

But the messages reveal that Professor Andersen later said: 'We describe this in the paper and say that this work is performed 'all of the world', but that isn't true - it has exclusively been going on at WIV'.

He then added: 'Given the data we had seen at the time of our writing, I was highly skewed towards 'natural'.

'But with some of this new data (plus stuff I didn't know previously), I'm moving much more towards the middle (again).'

Elsewhere, messages revealed the authors were aware that Dr Shi Zhengli, the WIV's leading bat coronavirus researcher, feared the pandemic may have been caused by a lab accident.

Professor Edward Holmes, from the University of Sydney, wrote in March 2021: 'Shi told them she was very worried about a lab escape and they did 2 internal audits and found nothing.

'This bit bothers me - and I mentioned this back when she made a similar comment to SciAm. It clearly shows she found it a likely explanation.'

Senator Paul wrote on X: 'Behind closed doors, the scientists who authored the Proximal Origin paper privately questioned their own conclusions.

'Publicly, however, they shamed, attacked, and censored those who raised legitimate questions – all in the name of damage control.

'We deserve accountability for every effort to keep the public in the dark.'

Share your thoughts with us in the comments