The finding is not the result of any new intelligence, and the report was completed at the behest of the Biden administration and former CIA Director William Burns.

It was declassified and released on Saturday on the orders of President Donald Trump’s pick to lead the agency, John Ratcliffe, who was sworn in Thursday as director.

The nuanced finding suggests the agency believes the totality of evidence makes a lab origin more likely than a natural origin.

But the agency’s assessment assigns a low degree of confidence to this conclusion, suggesting the evidence is deficient, inconclusive or contradictory.

Earlier reports on the origins of COVID-19 have split over whether the coronavirus emerged from a Chinese lab, potentially by mistake, or whether it arose naturally.

The new assessment is not likely to settle the debate. In fact, intelligence officials say it may never be resolved, due to a lack of cooperation from Chinese authorities.

The CIA “continues to assess that both research-related and natural origin scenarios of the COVID-19 pandemic remain plausible,” the agency wrote in a statement about its new assessment.

Instead of new evidence, the conclusion was based on fresh analyses of intelligence about the spread of the virus, its scientific properties and the work and conditions of China’s virology labs.

Lawmakers have pressured America’s spy agencies for more information about the origins of the virus, which led to lockdowns, economic upheaval and millions of deaths. It’s a question with significant domestic and geopolitical implications as the world continues to grapple with the pandemic’s legacy.

Republican Senator Tom Cotton of Arkansas, chairman of the Senate Intelligence Committee, said on Saturday he was “pleased the CIA concluded in the final days of the Biden administration that the lab-leak theory is the most plausible explanation” and he commended Ratcliffe for declassifying the assessment.

“Now, the most important thing is to make China pay for unleashing a plague on the world,” Cotton said in a statement.

China’s embassy in Washington did not immediately return messages seeking comment. Chinese authorities have in the past dismissed speculation about COVID’s origins as unhelpful and motivated by politics.

While the origin of the virus remains unknown, scientists think the most likely hypothesis is that it circulated in bats, like many coronaviruses, before infecting another species, probably racoon dogs, civet cats or bamboo rats. In turn, the infection spread to humans handling or butchering those animals at a market in Wuhan, where the first human cases appeared in late November 2019.

Some official investigations, however, have raised the the question of whether the virus escaped from a lab in Wuhan. Two years ago a report by the Energy Department concluded a lab leak was the most likely origin, though that report also expressed low confidence in the finding.

The same year then-FBI Director Christopher Wray said his agency believed the virus “most likely” spread after escaping from a lab.

Ratcliffe, who served as director of national intelligence during Trump’s first term, has said he favours the lab leak scenario, too.

“The lab leak is the only theory supported by science, intelligence, and common sense,” Ratcliffe said in 2023.

The CIA said it would continue to evaluate any new information that could change its assessment.