New research has put forward "strong evidence" that a Wuhan market was the source of the Covid-19 pandemic and suggests the World Health Organisation may have got a crucial timeline wrong.
The study from University of Arizona evolutionary biology Professor Michael Worobey was published in the prestigious journal Science and casts doubt on the theory the virus leaked from a Chinese laboratory.
Prof Worobey combed through hospital records, media reports and other data about the earliest Covid-19 cases to investigate the origins of the virus.
He now believes the first known case was a woman who worked as a seafood vendor at the market, not a 41-year-old accountant as suggested by the WHO in its report on the origins of the virus.
He noted the male accountant, who lived 30km south of Huanan Market in Wuhan and had no connection to it, said in a media interview that his symptoms started on December 16, not December 8 as the WHO appears to suggest.
This is backed by hospital records and other data.
The mix-up appears to relate to an earlier medical emergency the man experienced on December 8 which Prof Worobey suggests was actually due to a dental problem.
In a later interview, the man said he believed he had got infected with Covid while in hospital (possibly at the time of his dental emergency) or on public transport on the way home.
This would make a female seafood vendor, who got symptoms on December 11, almost a week earlier, the first Covid case.
Prof Worobey tweeted that his research "dramatically changes the picture put forward by the joint China-WHO study report" which focused on the 41-year-old accountant as being the first case.
He said the man's case had been used by "lab leak proponents to argue that the virus could not have emerged at the market" as the man had not visited it.
"It has led claims that the pandemic started at the BSL4 facility of the Wuhan Institute of Virology, since it is near where this guy lived and shopped," Prof Worobey tweeted.
"Turns out he just had a dental problem on December 8."
Prof Worobey said in his paper most early symptomatic cases were linked to Huanan Market, specifically where raccoon dogs were caged and "provides strong evidence of a live-animal market origin of the pandemic".
Wrongfully identifying the accountant as the first reported case of Covid has been used to discredit the "natural origin" theory that the virus was passed to an animal host before spreading to humans (possibly at the market). Instead, it fanned theories the virus was created in a lab and accidentally leaked into the community.
Prof Worobey said he was confident the accountant's case "loomed large" in US President Joe Biden's intelligence community review, leading the Federal Bureau of Investigation (FBI) to favour the lab leak idea and for other agencies to have "low confidence" in the idea of a natural origin of the virus.
But Prof Worobey said "you can't explain away the preponderance of early cases linked to Huanan Market".
"Many have dismissed the idea of the virus emerging at the market by arguing that all the focus by epidemiologists on the market led to lots of cases being identified there, while a vast number of cases elsewhere in the city were missed. This is just not true," Prof Worobey tweeted.
"The pattern was there in the very first hospitals that noticed the outbreak, *before* epidemiologists even started looking for cases.
"And this means that in all likelihood the pandemic started at the market."
Prof Worobey believes the strength of his article is that it draws on "first-hand accounts" including audio/video recordings of doctors, hospital administrators and patients like Zhang Jixian, Xia Wenguang, Wei Guixian, Chen Honggang, Ai Fen and Yuan Yufeng.
It is not the first time the WHO report has been called into question, with The Washington Post discovering several problems with data, including the wrong virus sequence IDs for three early patients.
The WHO report published in March this year found "no firm conclusion" could be made about the role of the Huanan market to the origins of the Covid outbreak but also that a laboratory incident was "extremely unlikely".
However, World Health Organisation director-general Tedros Adhanom Ghebreyesus later backflipped, saying the organisation was premature to rule out that a leak from a lab in Wuhan could have caused the Covid-19 pandemic.
He called on China to be more co-operative in the next phase of investigations into the pandemic origins, demanding more access to raw data.