Experts fielded questions about the possibility that the COVID-19 pandemic originated from a “lab leak” in Wuhan, China, during a hearing of a subcommittee for the House Committee on Space, Science and Technology, on Wednesday.

Two microbiologists explored a range of theories, with neither ready to scrap the possibility of a “lab-associated mechanism.” One of the microbiologists also called attention to the “risky” research being conducted by scientists in Wuhan.

In late May, President Biden called on U.S. intelligence officials to investigate the issue, including the possibility of a lab accident or leak, and to report back in 90 days.

Republicans have been calling for a hearing on the origins of the virus for months.

During his opening remarks, Subcommittee Chair Bill Foster (D-Ill.) explained that Democrats had prioritized responding to the pandemic, but now with vaccines succeeding and cases waning, it seemed appropriate to begin examining how the virus began.

“If we don’t learn everything that we can about how infectious diseases like COVID-19 get started, we will be less safe moving forward,” Foster said.

With regard to China’s potential role in the pandemic, he noted that the Chinese government withheld information and “obfuscated efforts” to understand the origin of the virus. The Chinese government’s lack of transparency in relation to an international health emergency is a “very serious geopolitical and science concern,” he said.

But “the absence of data is not itself evidence of a lab leak or something more sinister,” Foster added.

The subcommittee’s Ranking Member, Jay Obernolte (R-Calif.), while applauding the chairman’s bipartisanship, said he was frustrated by the lack of “fair and open public discourse” around the origins of SARS-CoV-2. He argued that the media and “Big Tech” were so wedded to a “preordained narrative” around how the virus began that they dismissed any other hypotheses as “xenophobic conspiracy theories.”

Expert witnesses also shared their perspectives on how the virus may have started and how it found its way into humans.

David Relman, MD, a microbiologist and professor at Stanford University School of Medicine in California, unpacked the two competing origin theories: First, that through a “natural spillover” the virus “jumped” from a bat to a human, or from a bat to another animal and then to a human.

A second theory is that the virus has a “laboratory-associated mechanism,” said Relman, who is also a senior fellow at Stanford’s Center for International Security and Cooperation.

The evidence for a natural spillover stems from the fact that “nearly all previous outbreaks” first identified in animals are believed to have natural origins, he added. Also, because of the broad diversity of coronaviruses, the idea persists that a viral source is “out there” but has yet to be found. He also pointed to the “extensive wildlife trade” in China, which could have played a role in the virus jumping from animals to humans and noted that “natural spillovers happen much more often than we had thought.”

The second argument, the “lab-leak” theory, is based on the fact that “the closest known relatives of SARS CoV-2” were found more than 1,000 miles from Wuhan, but the laboratory with the largest collection of bat-associated coronaviruses in the world is in Wuhan. He also cited the “risky work” occurring at laboratories in Wuhan and the fact that lab accidents also happen “more often than we had thought.” Additionally, he pointed to the lack of transparency and incomplete data samples and sequences shared by those laboratories.

“Neither hypothesis can be ruled in nor ruled out,” Relman said. “Both are plausible.”

On questioning by committee members, Relman expanded on the concerns over the risky studies being conducted at the Wuhan Institute of Virology. One of these studies began with a bat coronavirus known as WIV1, which had previously been studied and was known to be a “virus poised for human emergence,” he explained. And one of the ways researchers at the institute studied other novel samples was to take a portion of the genome sequence and insert it into the WIV1 virus.

“They then resurrected a few of those viruses and grew them in the laboratory,” Relman continued. “So, now we’re talking about a chimeric virus with properties that we don’t know … Those are experiments that concern me.”

“And I’m not saying that they led to this outbreak or pandemic by any means. But it’s simply the kind of work that I think we as a scientific society need to think much more clearly and more deliberately about before we undertake it,” he added.

In his own opening remarks, Stanley Perlman, MD, PhD, of the University of Iowa in Iowa City, eliminated the idea of a virus that was developed entirely “from scratch” in a laboratory as not being a “viable possibility,” but questioned whether a “naturally derived virus” could have been manipulated.

If that were the case, Perlman said, someone would have had to choose the precise coronavirus to manipulate and then know how to perform those manipulations. Another thought is whether a naturally derived coronavirus could have been adapted to grow in a new cell type. However, he noted, “most bat SARS-CoV-related viruses do not grow well in cell culture and … exist in the laboratory only as nonviable RNA.”

Perlman said that generally speaking, only certain viruses are capable of growing in cross-species tissue culture cells, and most will lose disease potential when grown in a new cell culture.

“This leaves a naturally derived virus, not manipulated in the laboratory, as the most likely source of SARS CoV-2,” he said.

Regarding the question of how the virus moved from animals to humans, Perlman said the virus could have been transported to Wuhan by an infected human or an infected animal. He said there is growing evidence to suggest that wildlife, such as raccoons, dogs, and minks are susceptible to SARS CoV-2, some of which were traded at the Wuhan seafood market.

The other possibility is that the virus was released or leaked from a laboratory in Wuhan, which does have several virology laboratories. The virus might have been introduced to the lab by someone working with an infected animal and that person or someone else could have been infected with the virus and, in theory, spread it in his or her community.

This possibility “cannot be ruled out and must be appropriately investigated,” Perlman noted.