The controversial theory Covid-19 was leaked from a Wuhan laboratory has once again gained momentum in the US, enraging China who vehemently reject such claims.
The US government's position has shifted to agnosticism in recent weeks, with top pandemic advisor Anthony Fauci and Centers for Disease Control and Prevention director Rochelle Walensky both saying they are open to all possibilities.
"We need to get to the bottom of this and we need a completely transparent process from China, we need the WHO (World Health Organisation) to assist in that matter," senior White House Covid adviser Andy Slavitt said on Tuesday.
WHO chief Tedros Adhanom Ghebreyesus himself fuelled the theory, calling for further investigations into the Wuhan Institute of Virology despite the highly-anticipated joint report stating the theory was "highly-unlikely".
"I do not believe that this assessment was extensive enough," he said in late March.
Australia was among a raft of WHO member states who this week called for a more in-depth investigation into the virus's source.
The theory was again catapulted into the spotlight earlier this week when a Wall Street Journal (WSJ) exclusive report claimed three employees from the laboratory were hospitalised with a seasonal illness in November 2019, citing a US intelligence report.
Former US secretary of state Mike Pompeo had previously stated the US had significant evidence to indicate the virus had leaked from the lab.
China lashes latest virus claims
Yet the latest focus on the theory has enraged China, with Yuan Zhiming, director of the institute's Wuhan National Biosafety Laboratory, saying the WSJ report was "a complete lie".
"Those claims are groundless. The lab has not been aware of this situation, and I don't even know where such information came from," he told the Global Times.
Addressing reporters on Monday evening, Foreign Ministry spokesperson Zhao Lijian hit out at the claims, insisting they are "totally untrue".
He cited meticulous records kept by the laboratory, stressing they indicated there had been zero infections logged.
Mr Zhao lambasted the global politicisation of the theory, saying Western experts conducted a thorough examination of the lab and its data.
However Scott Gottlieb, a former head of the Food and Drug Administration, told CNBC the failure to find the intermediary species believed to have brought the virus to Wuhan added to the speculation.
"The question for a lot of people is going to be when are too many coincidences too much?" he asked.
Dr Fauci echoed Tedros's remarks saying further investigations are needed while the source remains a mystery.
Former US president Donald Trump, whose government repeatedly peddled the theory, spoke out over the latest claims.
"Now everybody is agreeing that I was right when I very early on called Wuhan as the source of Covid-19," he said on Tuesday.
"To me it was obvious from the beginning but I was badly criticised, as usual. Now they are all saying 'He was right.' Thank you!"
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