The virus that triggered the ongoing pandemic probably emerged from markets in China that sold animals both dead and alive, according to a major investigation by the World Health Organization (WHO). While revealing, the findings aren’t conclusive and the WHO said it will keep all hypotheses under consideration.

The investigation looked at different hypotheses on when and where the pandemic started, finding that the virus likely didn’t spread widely before December 2019 or escape from a laboratory. The investigation report called for further research into wildlife and domestic animal farms in China and the global wildlife trade. This is in line with previous findings, but cannot fully exclude other possibilities.

“We could show the virus was circulating in the market as early as December 2019,” Peter Ben Embarek, who co-led the investigation, told Nature. “A lot of good leads were suggested in this report, and we anticipate that many, if not all of them, will be followed through because we owe it to the world to understand what happened.”

Global research

Over 30 scientists from around the world participated in the investigation by traveling to Wuhan, where the pandemic started and collecting data. They largely focused on the COVID-19 cases that happened in December 2019 and January 2020, looking to see where exactly the pandemic was most likely to start. Two-thirds of those who had symptoms in December had been exposed to live or dead animals, they argued in the report.

The genomes of SARS-CoV-2 from some of the people in this group were sequenced, finding that eight of the earliest sequences were identical, and that infected people were linked to the Huanan market – where the COVID-19 was first detected. The researchers also found that the genomes varied from earlier cases, which suggests the virus could have been spreading under the radar — meaning the wet market may have not been the original event, but an early spreader.

The scientists found that many animals were sold at the market, from rabbits and crocodiles to poultry and salamanders. While Chinese officials argued the market didn’t sell live mammals or illegal wildlife, the report included references from unverified media reports that suggest this wasn’t the case. Nevertheless, exactly what happened at the Huanan market remains unknown.

Over 1,000 samples were collected from the market in early 2020, swabbing bins, toilets, and stalls. The ones that tested positive were mainly from stalls that sold seafood, livestock, and poultry, the report found. Researchers also traced back animals at the market back to three provinces in China where pangolins and bats carrying coronaviruses had been found.

Animal spillover is still the most likely option

In another relevant finding, the WHO report also concluded that it’s very unlikely that the novel coronavirus escaped from a lab at the Wuhan Institute of Virology, a possibility that was mentioned in the past by a few researchers and promoted by the CDC ex-director. Still, most scientists have supported the hypothesis of SARS-CoV-2 having spilled over from animals into humans.

The WHO team visited the laboratory in Wuhan and were told by the scientists that none in the lab had antibodies against SARS-CoV-2 – dismissing the possibility of someone there having been infected in an experiment. The researchers at the lab also said they hadn’t kept any live virus strains similar to SARS-CoV-2 and said everyone in the team had safety training.

“So what we found, I think, is pretty important evidence of a way the virus could have emerged from rural China into a big city like Wuhan and led to an outbreak,” WHO team member Peter Daszak told CNN. “And it turns out that at the end of the report, both the China team of experts and the WHO experts all felt this was the most likely pathway that the virus took.”

However, the new report is unlikely to deter supporters of the lab escape hypothesis. Even as there is no evidence to support this hypothesis (and there is evidence to support animal spillover), the fact that it was not 100% disproven will likely not settle the debate. However, WHO’s Peter Ben Embarek, who co-led the investigation notes that this investigation is far from the last: a lot of good leads were suggested in the report, and they will all be followed by more in-depth research, Embarek notes. WHO director-general, Tedros Adhanom Ghebreyesus, who was not directly involved with the investigation, posted a statement saying:

“I do not believe that this assessment was extensive enough,” he wrote. “This requires further investigation, potentially with additional missions involving specialist experts, which I am ready to deploy.”

This suggestion of new steps is particularly important because China did not share all its existing information with the WHO.

China withheld information

While comprehensive, the report had significant limitations as China refused to provide raw data on early COVID-19 cases to the WHO team. They had requested data on 174 cases that China had identified from the early phase of the outbreak in Wuhan in December 2019, as well as other cases, but were only provided with a summary.

Dominic Dwyer, an Australian infectious diseases expert who is a member of the team, told Reuters gaining access to the raw data was especially important since only half of the 174 cases had exposure to the Huanan market. Dwyer said the WHO team had “arguments” with their Chinese counterparts over the significance of the data.

WHO Director-General Tedros Adhanom Ghebreyesus told Reuters that the researchers “expressed the difficulties they encountered in accessing raw data,” expecting that future collaborative studies can include “more timely and comprehensive data sharing.” He said the report wasn’t “extensive enough” and that further studies will be needed. Dr. Anthony Fauci, the top U.S. infectious diseases expert, noted that he’d like to read the report thoroughly to understand exactly what information China withheld. “I want to read the report first and then get a feel for what they really had access to — or did not have access to,” he told AP. Indeed, until we don’t find the exact source of the virus or have complete transparency about what happened in those early pandemic days, the matter likely won’t be definitively settled.

Although the report has not yet been made public (it will likely be made public within a week), several experts already have access to it and are reviewing it. White House press secretary Jen Psaki commented on this:

“I think he believes the American people, the global community, the medical experts, the doctors — all of the people who have been working to save lives, the families who have lost loved ones — all deserve greater transparency,” Psaki told reporters at a White House briefing.

“Seventeen experts, longstanding leaders from the field, including epidemiology, public health, clinical medicine, veterinary medicine, infectious disease, law, food security, biosafety, biosecurity — we have a lot of experts in government — will be reviewing this report intensively and quickly,” she said at a daily briefing.