China will test thousands of Wuhan blood samples from two years ago in a bid to shed new light on the origins of Covid-19.
However experts fear the process will be shrouded in secrecy and have called on Beijing to allow Western scientists to observe the process.
It comes as the The World Health Organisation said its newly formed advisory group on dangerous pathogens may be "our last chance" to determine the origins.
Once accused of kowtowing to Beijing in the pandemic's infancy, it has since gradually spoken more critically of China and urged authorities to share early data to assist new investigations.
Up to 200,000 blood samples from 2019 have been keep at the Wuhan Blood Centre, with tens of thousands expected to be tested by Chinese scientists, CNN reported.
The samples, which can only be accessed following a two-year period, will soon be available for the months of October and November – a key period in which experts believe undetected transmission may have occurred in the mega city long before the first reported case on December 8.
Maureen Miller, associate professor of epidemiology at Columbia University, told CNN the blood samples, which are from blood donors, will "absolutely contain vital clues".
Yet she expressed her concerns over how transparent Beijing will be and said it was vital foreign experts were there during the process.
"No one will believe any results that China reports unless there are qualified observers at the very least," she said.
China's opportunity to 'show they're serious'
The origins of the Covid-19 virus has been a contentious issue, with Beijing reacting angrily to suggestions from the West it failed in its response during the early weeks of the pandemic as well as allegations it covered up key information and the severity of the initial outbreak.
Australia faced the wrath of China after Prime Minister Scott Morrison made an early call for independent investigations into the origins of the virus – fuelling the fallout between the two countries.
China has also faced continued speculation the virus was leaked from the Wuhan Institute of Virology, a theory which WHO chief Tedros Adhanom Ghebreyesus said needed further investigation earlier this year.
Dr William Schaffner, from the Vanderbilt University Department of Medicine's infectious disease division, told CNN there could be issues with the integrity of the testing, suggesting China could use fake samples.
But Yanzhong Huang, senior fellow for global health at the Council on Foreign Relations, said the testing was an opportunity for China to "tell the world that they are serious about depoliticising the origins probe".
Beijing has routinely pointed to the emergence of the virus in other countries including France and Italy prior to it being discovered in Wuhan. It has also suggested the virus could have been intentionally brought to Wuhan by the US during the 2019 Military Games held in the city.
Western experts on an initial WHO-led mission to Wuhan at the beginning of the year said the virus likely jumped from bats to an intermediate animal before being transmitted to humans.
But Tedros said that the investigation was hampered by a dearth of raw data pertaining to the first days of the outbreak's spread and has called for lab audits.
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