Scientists say no evidence so far that virus leaked from China lab DebriefOrigin of virus

Scientists are no closer to finding out the origins of Sars-CoV-2, the virus that causes Covid-19, nearly two years after it was first reported in China.

An unclassified US intelligence summary report released on Friday said it was unable to determine if the coronavirus emerged naturally or was the result of an accidental leak from a laboratory. To date, more than 216 million Covid-19 cases and 4.5 million deaths have been recorded worldwide.

Covid-19 was first reported in the central Chinese city of Wuhan in December 2019, and spread rapidly across the globe. Since its emergence, various theories have surfaced over its origins.

Most experts believe the disease is of zoonotic origin. The World Health Organisation (WHO) team investigating the origins of Sars-CoV-2 earlier this year also suggested that the virus most likely infected humans from an intermediate animal host.

The US report said several organisations within the sprawling US intelligence community believed that the virus emerged from "natural exposure to an animal infected with it or a close progenitor virus", but they had only "low confidence" in that conclusion.

Former US president Donald Trump has suggested, without evidence, that the virus could have leaked from a Chinese lab, and has accused Beijing of spreading Covid-19 around the world. But the WHO team said it was extremely unlikely that the virus leaked from the Wuhan Institute of Virology, and that further research into this theory was not required.

A paper by 21 top virologists in the journal Cell published on Aug 18 said: "There is currently no evidence that Sars-CoV-2 has a laboratory origin."

The Chinese authorities have been pushing the narrative that the virus could have escaped from the biological defence site Fort Detrick in Maryland in 2019. Once the centre of the US biological weapons programme, Fort Detrick now houses biomedical labs researching viruses, including Ebola and smallpox.

Nationalist Chinese tabloid Global Times has launched an online petition urging the public to sign an open letter demanding that the WHO launch an investigation into Fort Detrick.

China also previously said the virus could have been brought into Wuhan via cold-chain logistics and frozen food products, linking the theory to various domestic outbreaks this year. The WHO mission appeared to give weight to China's theory that the virus could be carried on cold-chain products, although foreign experts, including WHO's top emergency expert, Dr Mike Ryan, and the US Centres for Disease Control and Prevention, have downplayed this risk.

Finding the original source of Sars-CoV-2 is key to understanding how to predict, prevent and contain future pandemics. This, in turn, could save lives and protect economies. "The question isn't whom to blame - it's whether you want another virus to kill millions more people in the next decade," the Los Angeles Times quoted Dr Alina Chan, a molecular biologist at the Broad Institute of MIT and Harvard, as saying. "When your house catches fire, it shouldn't be controversial to look closely at how it happened," Dr Chan said.

Experts say all possibilities are still on the table and require further study. But this will need China's cooperation, and the US report accused Beijing of hindering probes to trace the roots of the virus - a claim denounced by the Chinese as "scapegoating China".

President Joe Biden has said the US and its allies will continue to press the Chinese government for answers. WHO has also said it will be setting up a new committee to develop next steps on studying the virus. The US intelligence report, however, will further poison the US-China relationship, which is already at its lowest in decades.