It has been three years since COVID-19 pandemic began, yet one crucial question remains a mystery to governments and health agencies around the world: Did the virus originate in animals or leak from a Chinese laboratory?

Now, the U.S. Department of Energy has assessed with "low confidence" in that it began with a laboratory leak, according to a person familiar with the report who was not authorized to discuss it. The report has not been made public.

But others in the U.S. intelligence community disagree.

"There is not a consensus right now in the U.S. government about exactly how COVID-19 started," John Kirby, the spokesman for the National Security Council, said Monday. "There is just not an intelligence community consensus."

The DOE's conclusion was first reported over the weekend in the Wall Street Journal, which said the classified report was based on new intelligence and noted in an update to a 2021 document. The DOE oversees a national network of laboratories.

White House officials on Monday declined to confirm press reports about the assessment.

In 2021, officials released an intelligence report summary that said four members of the U.S. intelligence community believed with low confidence that the virus was first transmitted from an animal to a human, and a fifth believed with moderate confidence that the first human infection was linked to a laboratory.

While some scientists are open to the laboratory-leak theory, others continue to believe the virus came from animals, mutated, and jumped into people – as has happened in the past with viruses. Experts say the true origin of the pandemic may not be known for many years – if ever.

More investigation

Alina Chan, a molecular biologist at the Broad Institute of Massachusetts Institute of Technology and Harvard, said she is not sure what new intelligence the agencies had, but "it’s reasonable to infer" it relates to activities at the Wuhan Institute of Virology in China. She said a 2018 research proposal co-authored by scientists there and their U.S. collaborators "essentially described a blueprint for COVID-like viruses."

"Less than two years later, such a virus was causing an outbreak in the city," she said.

The Wuhan institute had been studying coronaviruses for years, in part because of widespread concerns – tracing back to SARS – that coronaviruses could be the source of the next pandemic.

No intelligence agency has said they believe the coronavirus that caused COVID-19 was released intentionally. The unclassified 2021 summary was clear on this point, saying, "We judge the virus was not developed as a biological weapon."

"Laboratory accidents occur at a surprising frequency. A lot of people don’t really hear about laboratory accidents because they're not talked about publicly," said Chan, who co-authored a book about the search for COVID-19 origins. Such accidents "underscore a need to make work with highly dangerous pathogens more transparent and more accountable."

Last year, the World Health Organization (WHO) recommended a deeper probe into a possible laboratory accident. Chan said she hopes the latest report sparks more investigation in the United States.

China has called the suggestion that COVID-19 came from a Chinese laboratory "baseless."

Animal theory

Many scientists believe the animal-to-human theory of the coronavirus remains much more plausible. They theorize it emerged in the wild and jumped from bats to humans, either directly or through another animal.

In a 2021 research paper in the journal Cell, scientists said the COVID-19 virus is the ninth documented coronavirus to infect humans – and all the previous ones originated in animals.

Two studies, published last year by the journal Science, bolstered the animal origin theory. That research found that the Huanan Seafood Wholesale Market in Wuhan was likely the early epicenter. Scientists concluded that the virus likely spilled from animals into people on two separate occasions.

"The scientific literature contains essentially nothing but original research articles that support a natural origin of this virus pandemic," said Michael Worobey, an evolutionary biologist at the University of Arizona who has extensively studied COVID-19's origins.

He said the fact that others in the intelligence community looked at the same information as the DOE and "it apparently did not move the needle speaks volumes." He said he takes such intelligence assessments with a grain of salt because he does not think the people making them "have the scientific expertise ... to really understand the most important evidence that they need to understand."

The U.S. should be more transparent and release the new intelligence that apparently swayed the DOE, Worobey said.