The Wuhan wet market is still the most likely hypothesis for the origin of the Covid-19 pandemic, members of a World Health Organisation delegation to China have said.
Four scientists who joined the month-long mission earlier this year said they had found no evidence to support theories that the outbreak was caused by an accidental lab leak.
They told a Chatham House briefing there was also nothing to support claims the disease was deliberately developed by China, and blamed conspiracy theories for delaying the mission.
Zoologist Dr Peter Daszak, president of NGO EcoHealth Alliance which works in the field of zoonotic disease, said the team had identified a viable conduit between the wet market in Wuhan and to regions where the closest relatives of Covid-19 are found in bats.
He said: “It provides a link and a pathway by which these viruses could convincingly spill over from wildlife into either people or animals farmed in the region and then shipped into the market by some means.”
Dr Daszak said the theory that the virus crossed into domesticated or farmed animals and got into the Wuhan market was the scenario that both the WHO scientists and their Chinese counterparts considered most likely.
The scientists said they found no evidence to support theories that the disease leaked from the three virology labs in Wuhan and they had been given access to all three.
Dr Marion PG Koopmans, head of viroscience at University Medical Centre Rotterdam, said: “We discussed the research programmes, the routine testing programmes, the way they work, what they had done in terms of health monitoring and testing of staff.
“Based on that we concluded that it’s extremely unlikely that there was a lab incident,” Dr Koopman said.
She added: “What we have been saying to people who are saying ‘it has to be something else’ then please provide what evidence you have to WHO and then it will be taken into consideration.
“We cannot work on the basis of speculation, we work on the basis of observation that we have,” she said.
Dr Daszak said that science had been “crushed” by factions pushing anti-China conspiracy theories – notably Donald Trump – to further their political agenda.
“We have not had access to work in China on the origins for the last 12 months which is ironic because we could have been on the ground there working with our Chinese colleagues and by now we might have had some really important answers as to how it emerged.”
David Heymann, professor of infectious disease epidemiology at the London School of Hygiene and Tropical Medicine and head of the Centre on Global Health Security at Chatham House, acknowledged the lab leak hypothesis is not in itself a conspiracy theory.
He told the briefing: “We know that lab accidents can occur and what the team is saying is that there is no conspiracy that there could have been a leak.
“But this conspiracy theory about manipulating a virus in a laboratory is what many people are basing their belief on and I think there is probably no evidence for that.”
Dr Daszak called for the threat of pandemics to be treated with the same level of seriousness as terrorism in the wake of the 9/11 attacks.
“We don’t put enough energy into forecasting pandemics and working out where the next ones are going to come from and what it might be, whereas we do that with hurricanes and typhoons and all the rest of it,” he said.
He added: “After 9/11 we put in place a mechanism to track every single phone call into the US and the minute there’s a rumour on the web or on these phone calls of an attack, the network is disrupted prior to the attack.
“That’s the kind of change or shift in thinking we need for pandemics I believe.”
Dr Daszak said: “Let’s look at where wildlife are interacting with livestock and people and see what is out there and try and find out what threats could emerge in future.”
He added: “That’s the strategy that will give us an incredible return on investment.”