The World Health Organization head has not refuted any COVID-19 origin theory and said that all hypotheses on how the deadly pandemic started remained on the table following the WHO’s investigation in China.

At a press conference in Geneva alongside Wuhan investigation team head Peter Ben Embarek, WHO director-general Tedros Adhanom Ghebreyesus said the team had conducted a “very important scientific exercise in very difficult circumstances”.

“Some questions have been raised as to whether some hypotheses have been discarded. Having spoken with some members of the team, I wish to confirm that all hypotheses remain open and require further analysis and studies,” Tedros said.

“Some of that work may lie outside the remit and scope of this mission. We have always said that this mission would not find all the answers, but it has added important information that takes us closer to understanding the origins of the virus,” he added.

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The investigation team to Wuhan, where the first cases were spotted, failed to identify the source of the virus but disapproved the theory that it leaked from a virology laboratory in the Chinese city.

At a press conference in Wuhan on Tuesday concluding the team of experts’ visit, Ben Embarek quashed the theory that a leak from a virology lab in Wuhan could have caused the pandemic — a notion propagated by former US president Donald Trump.

“The laboratory incident hypothesis is extremely unlikely,” Ben Embarek had said. It “is not in the hypotheses that we will suggest for future studies.”

In Geneva on Friday, he said the team had been told by the Wuhan laboratories they visited and spoke to that none of them had been working on or had SARS-CoV-2 — the virus that causes COVID-19 disease — in their collections.

“It’s of course always possible that the virus is and was present in samples that have not yet been processed, or among viruses that have not yet been characterised,” he said.

“But knowingly, apparently from all the labs we’ve talked with, nobody has seen this virus before.”

Ben Embarek added that the common practice for scientists discovering new viruses was to publish their findings immediately.

Experts believe the disease originated in bats and could have been transmitted to humans via another mammal.

The first COVID-19 cases were reported in Wuhan in December 2019. More than 2.3 million people worldwide have since been killed by the virus.

The international investigation in the city only began in January 2021.

Tedros said he hoped a summary report from the mission would be published next week, with the full final report to follow in the coming weeks.