New sequences of the SARS-CoV-2 virus as well as additional genomic data based on samples taken from a live animal market in Wuhan, China, in 2020 were briefly uploaded to the GISAID database by Chinese scientists earlier this year, allowing them to be viewed by researchers in other countries, according to the WHO's Scientific Advisory Group for the Origins of Novel Pathogens (SAGO).
The sequences suggest that raccoon dogs were present in the market and might have also been infected by the coronavirus, providing a new clue in the chain of transmission that eventually reached humans.
Access to the information was subsequently restricted "apparently to allow further data updates" by the Chinese Centre for Disease Control and Prevention (CDC).
WHO officials discussed the matter with Chinese colleagues, who explained the new data was intended to be used to update a preprint study from 2022.
China's CDC plans to re-submit the paper to the scientific journal Nature for publication, according to SAGO's statement.
WHO officials say such information, while not conclusive, represents a new lead into the investigation of COVID-19's origins and should have been shared immediately.
"These data do not provide a definitive answer to the question of how the pandemic began, but every piece of data is important in moving us closer to that answer," WHO Director-General Tedros Adhanom Ghebreyesus said on Friday.
"These data could have - and should have - been shared three years ago.
"We continue to call on China to be transparent in sharing data, and to conduct the necessary investigations and share the results."
SAGO was tasked by the WHO to continue to investigate the origins of the pandemic that has killed nearly seven million people worldwide.
The Huanan Seafood Wholesale Market in Wuhan was shut down by Chinese authorities after the novel coronavirus emerged in the city in late 2019.
The market has since been a focus of study of whether the virus had infected several other species before jumping to humans.
The WHO and other scientists have also said they cannot rule out the possibility that the virus emerged from a high-security laboratory in Wuhan that studies dangerous pathogens. China denies any such link.
The 2022 preprint paper said a small portion of 923 samples collected from the stalls and sewage systems in and around the market tested positive for the virus; no virus was detected in 457 animal samples tested.
The paper said initially that raccoon dogs were not among the animals tested.
The new analysis suggests "that raccoon dog and other animals may have been present before the market was cleaned as part of the public health intervention", SAGO said.
