An analysis of public information by Republican staff of the Senate Committee on Health, Education, Labor and Pensions concluded that the COVID-19 pandemic was “more likely than not a research related incident.”

A 35-page interim report released Thursday concludes that the epidemiology of the early pandemic starkly differs from how other airborne epidemics first emerged in humans and spread.

The interim report echoes aspects of other nascent investigations into the origins of COVID-19: The Lancet Commission report and the World Health Organization’s Scientific Advisory Group on the Origins of Novel Pathogens interim report. The U.S. Office of the Director of National Intelligence 90-Day Assessment on COVID-19 Origins was also inconclusive on the matter of the “lab leak” hypothesis.

The report also follows a report released by House Foreign Affairs Committee Republicans last year that reached similar conclusions. The ranking members of several key committees have indicated an interest in investigating the origins of COVID-19 if Republicans gain control of either chamber of Congress after next month’s midterm elections.

According to the new report, the COVID-19 pandemic appears to have emerged in Wuhan, China, without a trace.

The new report asks why SARS-CoV-2 left behind so few clues in its wake before emerging in humans, and whether those clues might in fact be found in the Wuhan Institute of Virology.

“​​The available evidence appears to be inconsistent with both historic precedent and the scientific understanding of how natural zoonotic spillovers of respiratory viruses like SARS-CoV-2 occur,” the report states.

The emergence of SARS-CoV-2 represents a “a significant break from the precedent of other zoonotic spillovers involving respiratory viruses, such as MERS and SARS,” the report continues.

The closest cousin viruses to SARS-CoV-2 were discovered in rural Southeast Asia and Yunnan Province, yet SARS-CoV-2 appears to have arrived in the metropolis of Wuhan, China, without leaving an obvious trail in wildlife or in the rural populations along the way.

The report argues that the absence of evidence along the hundreds of miles that separate southern China and Wuhan stands in stark contrast to the evidence that early SARS cases left behind in 2002.

Virologists consider it unlikely that SARS-CoV-2 became human-adapted in bats because of key differences in our immune systems (though the report concedes it is possible.)

Yet nearly three years after SARS-CoV-2 first emerged, an “intermediate host” — a reservoir of other mammals in which the virus could have evolved the changes it needed to infect and spread among humans — has not been identified.

By contrast, Chinese authorities had identified SARS infections in palm civets and raccoon dogs within six months of the first human case of SARS, the report points out. This animal reservoir continued to cause infections. Yet with SARS-CoV-2, it has not been shown that infected animals continued to drive infections outside the Huanan Seafood Market in Wuhan.

Yet the virus emerged primed to infect and transmit in human populations. (Former White House COVID Response Coordinator Deborah Birx said earlier this year that COVID-19 “came out of the box ready to infect.”)

Meanwhile, many Western virologists have said that the evidence points unambiguously to the Huanan Seafood Market as the early epicenter of cases.

Many early cases were tied to the market, and even cases without a direct tie to the market appear centered in the surrounding area.

Michael Worobey, a University of Arizona evolutionary biologist and lead author of a well publicized paper tying early COVID-19 cases to the Huanan Seafood Market, pushed back on the Senate report a few hours ahead of publication on Twitter.

Worobey stated that the absence of an obvious intermediate animal or better evidence that SARS-CoV-2 circulated in an animal reservoir is “an evidentiary gap” but “not significant,” citing his paper and a sister paper describing the early evolution of SARS-CoV-2 as two separate zoonotic spillovers.

“Our two recent papers establish that a natural zoonotic origin is the only plausible scenario for the origin of the pandemic,” Worobey wrote. “The Senator’s commission’s report cannot change the scientific evidence.”

Worobey has dismissed claims that Chinese authorities’ focus on the market might have biased the very early data.

But the report also cites the genetic similarity between samples taken from market stalls and human viral samples. They indicate that the market was a human superspreader event, not the epicenter of a zoonotic spillover, the report states, citing a preprint authored by Chinese virologists that has received criticism from the Western virologists.

The report includes a spatial distribution map of users of the Chinese social networking site Weibo who searched for help for flu-like symptoms from late December to mid-January, and found they were more closely clustered around the Wuhan Institute of Virology.

Worobey has said the evidence proves the virus emerged naturally and that continuing to speculate about a lab origin of COVID-19 jeopardizes trust in science.

“Those promoting conspiracy theories and attacking scientific findings that don’t break in the direction they wish, regardless of how well credentialed, inflict extraordinary damage on our ability to effectively advance global health,” Worobey recently wrote in Foreign Policy.

In contrast, the report states that key questions about the origin of COVID-19 remain unanswered.

It remains a mystery, the committee staff write, how SARS-CoV-2 acquired its furin cleavage site. The furin cleavage site is a feature on the virus’s spike protein that makes it especially dangerous. Furin cleavage sites do not appear to occur in other SARS-like viruses. But the report notes that researchers working with the Wuhan Institute of Virology authored a grant report laying out plans to test furin cleavage sites in SARS-like viruses, though it remains unclear whether this research was performed.

The Wuhan Institute of Virology’s interest in evaluating the pandemic potential of bat coronaviruses this way, combined with evidence that the WIV struggled to safely run its new maximum biocontainment lab in the years before the outbreak, also persuaded the committee Republicans that a lab origin is more likely.

“Advocates of a zoonotic origin theory must provide clear and convincing evidence that a natural zoonotic spillover is the source of the pandemic, as was demonstrated for the 2002-2004 SARS outbreak,” the report states. “In other words, there needs to be verifiable evidence that a natural zoonotic spillover actually occurred, not simply that such a spillover could have occurred.”