The Covid-19 virus most likely leaked from a laboratory in Wuhan, China, according to the US Energy Department.
A report seen by the Wall Street Journal said the agency had updated its position in light of ‘new intelligence’ and the latest science on the virus.
It previously said it was ‘undecided’ on how the pandemic started, adding that its new stance is scientifically speaking held with ‘low confidence’.
The FBI previously reached the same conclusion with ‘moderate confidence’, while four other US agencies believe the pandemic was likely caused by natural transmission and another two remain undecided.
The report, said to have been handed to the White House and senior members of Congress, also stated the virus was probably not engineered as part of a weapons program.
Researchers have widely dismissed conspiracy theories that the virus was deliberately created in the Wuhan Institute of Virology, a lab known to carry out classified research in the city where the first cases were identified.
But a number of independent studies published in major academic journals have said samples of the virus or its ancestors could plausibly have been collected from elsewhere in China for further study in Wuhan.
Jake Sullivan, the White House national security adviser, said there were still a ‘variety of views’ on the issue among American officials.
But the latest findings further undermine the World Health Organisation’s insistence that the lab leak theory is ‘extremely unlikely’.
The WHO’s chief Tedros Adhanom Ghebreyesus has nonetheless said all theories on the origin of the virus remain on the table and has called on Beijing to allow further investigation.
The energy department’s classified findings reportedly said in 2021 that three researchers from the Wuhan institute involved in coronavirus research were hospitalised due to illness in November 2019.
In the absence of evidence from Chinese laboratories, a clear answer on the origin of the virus may never be found.
A major obstacle often cited by scientists is that tracing the ancestry of coronaviruses is extremely difficult and becomes harder as time passes.
Several close relatives of the Covid-19 virus have been found in bats and pangolins across China and south-east Asia, but they have been found to mutate frequently while hopping back and forth between animals.
Virologists at the University of Sydney last year said the chances of finding a direct ancestor are ‘almost nil’, adding: ‘That ship has sailed.’
The Department of Energy’s main responsibilities are energy production, national security and sponsoring scientific research.
While it is not directly involved in investigating viral diseases, it oversees a network of 17 laboratories including some which deal with advanced biology.
Mr Sullivan added: ‘President Biden specifically requested that the national labs, which are part of the Energy Department, be brought into this assessment because he wants to put every tool at use to be able to figure out what happened here’.
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