A long-awaited report into the origins of Covid-19 “raises further questions” that need more research, the head of the World Health Organization said on Tuesday, calling for “more timely and comprehensive” data sharing in the future.
WHO director general Tedros Adhanom Ghebreyesus said that the source of the virus was still unknown and pledged “to leave no stone unturned” to find it.
The report, and its conclusions, have been the subject of intense global scrutiny since the team of international and WHO scientists finished their visit this year to Wuhan, where the virus was identified in late 2019.
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The report is the culmination of a 28-day mission to Wuhan, the city where the virus first emerged. WHO member states started calling for an investigation last May, but international inspectors were not able to visit China until January.
The report has also been a source of political contention. The US has questioned its independence from the Chinese government, while Beijing has insisted it has been transparent and has accused Washington of politicising scientific work.
“[The report] raises further questions that will need to be addressed by further studies,” said Tedros in a speech to member states on Tuesday.
“In my discussions with the team, they expressed the difficulties they encountered in accessing raw data. I expect future collaborative studies to include more timely and comprehensive data sharing.
“This report is a very important beginning, but it is not the end. We have not yet found the source of the virus, and we must continue to follow the science and leave no stone unturned as we do.”
The report, the result of a joint effort by 17 Chinese and 17 international researchers, concludes that it was “likely to very likely” the virus spread to humans from a bat or other host animals via an intermediary animal that was in close contact with humans.
It also said that it was “possible to likely” that the virus had spread directly from bats to humans, and it was “possible” it had spread through cold-chain food products.
The final hypothesis, that the virus was the result of a laboratory leak, was ranked “extremely unlikely” – and unlike the other theories, the report did not recommend any follow-up studies.
The assessment was made because there was no record of closely related viruses in any laboratories before December 2019, when the disease first emerged. It also said the three labs in Wuhan working with coronaviruses were “high quality … well-managed” facilities with no record of compatible illness or indications of infection before that date.
The laboratory theory, which was promoted by former US president Donald Trump and his allies, has been vehemently rejected by China.
It has also been viewed sceptically by the broader scientific community, though some researchers say that a thorough audit, which was not within the scope of the mission, would be needed to rule it out entirely.
In his comments to member states, Tedros said: “Although the team has concluded that a laboratory leak is the least likely hypothesis, this requires further investigation, potentially with additional missions involving specialist experts, which I am ready to deploy.”
The report also provides suggestions on how the other scenarios could be investigated.
These recommendations include studies outside China – something Beijing has long claimed would be necessary, as it suggested the virus could have originated outside its borders.
The report also provides an insight into the efforts to understand the start of the outbreak and find previously unknown cases before December 2019.
It also provides details on the search for infected animals that may have helped transmit the virus.
The report recommends more sampling of potential host animals like bats and pangolins in China and other countries where close viral relatives have been found. It also recommends research into wildlife farms supplying Wuhan from regions known to harbour bats carrying related viruses.
The report also notes that no evidence was found for substantial transmission of the Sars-CoV-2 coronavirus in the months preceding the outbreak in December 2019. But earlier transmission of Sars-CoV-2 could not be ruled out on the basis of the evidence collected, the report said, and more extensive study and testing was needed.
Some scientists said that the report, while not conclusive, provided a useful foundation for further investigation.
“I do think the WHO team were asking the right questions, and that they did do a good job making a clear outline of what has been done and what needs to be done,” said evolutionary virologist Edward Holmes, a professor at the University of Sydney in Australia.
“The idea that they’ll go there in a couple of weeks and find the origin, that clearly is not going to happen,” he said.
The report was leaked on Monday, with several outlets presenting its contents ahead of the WHO’s schedule. Some scientists were critical of the report for downgrading the lab leak theory without taking into account that laboratories at the Wuhan Institute of Virology were manipulating bat coronaviruses to make them more easily transmissible to humans, a controversial practice known as gain-of-function research.
“It remains vitally important that we understand how Sars-CoV-2 virus from the very first known human infections was so exquisitely well adapted to not only infect but also to transmit between humans, a feature not typical of other zoonotic virus spillovers to humans at their origin,” said Nikolai Petrovsky, a professor of medicine at Flinders University in Adelaide, Australia.
“This report does nothing to address this key and unique feature of Sars-CoV-2 and how this came about.”
At the WHO news conference on Tuesday, mission member Dr Dominic Dwyer, a professor of medicine at the University of Sydney, said that the team was able to discuss biosecurity protocols with the researchers at the Wuhan Institute of Virology but that the team was not there to do a “forensic investigation”.
Peter Embarek, the leader of the WHO-appointed group of experts, added that there were gaps in the raw data collected by Chinese researchers before the mission’s arrival to Wuhan.
Dr Thea Fischer, a professor of medicine at the University of Copenhagen, also said at the Tuesday news conference that one of the most important recommendations to fill these gaps was a joint analysis of blood donor samples during the months preceding the first outbreak.
Additional reporting by Eduardo Baptista
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