There is no evidence yet showing which animal the Covid-causing virus may have come from, the former head of the Chinese centre for Disease Control and Prevention (CDC) said on Friday.
George Gao, who was speaking at a London summit on preparing for pandemics, was the head of the agency when Covid first emerged in Wuhan, China, at the end of 2019.
"Even now, people think some animals are the host or reservoir," said Gao. "Cut a long story short, there is no evidence which animals (were) where the virus comes (from)."
The origins of the Covid-19 pandemic remain unknown, with criticism that China has thwarted efforts to find out more. The Chinese government has said it has always supported all efforts to investigate the source.
The World Health Organisation has said that all hypotheses for the origins of Covid-19 remain on the table, including that the virus is linked to a high-security laboratory for the study of dangerous pathogens in Wuhan.
China denies any such link.
WHO has also said that the evidence so far points towards the virus coming from animals, likely bats.
Data from the early days of the pandemic was uploaded to a global database by Chinese scientists last month.
It included genetic sequences found in more than 1,000 environmental and animal samples taken in January 2020 at the Huanan seafood market in Wuhan.
The data showed that DNA from multiple animal species - including raccoon dogs - was present in environmental samples that tested positive for SARS-CoV-2, the virus that causes Covid, suggesting that they were "the most likely conduits" of the disease, according to a team of international researchers.
Speaking at the Rhodes Policy Summit, Gao also said that the world needed to work together to tackle future outbreaks. That would include some elements of competition, he said, but also communication, to combat misinformation.