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The origin of coronavirus is still unclear and the theory that it was caused by a laboratory leak in the Chinese city Wuhan should not be ruled out, a leading group of scientists have said.
In a letter to the Science journal the 18 experts, including Ravindra Gupta, a clinical microbiologist at the University of Cambridge, and Jesse Bloom, who studies the evolution of viruses at the Fred Hutchinson Cancer Research Center, said the possibility needs to be explored until a rigorous data-led investigation proves it wrong.
COVID-19, which emerged in China in late 2019, has killed 3.34 million people worldwide, cost the world trillions of pounds in lost income and upended normal life for billions of people.
"More investigation is still needed to determine the origin of the pandemic," said the group in the open letter to Science.
"Theories of accidental release from a lab and zoonotic spillover both remain viable."
The authors of the letter, who also include David Relman, professor of microbiology at Stanford, said the World Health Organization's (WHO) investigation into the origins of the virus had not made a "balanced consideration" of the theory that it may have come from a laboratory incident.
In its final report, written jointly with Chinese scientists, a WHO-led team that spent four weeks in and around Wuhan in January and February said the virus had probably been transmitted from bats to humans through another animal, and that a lab leak was "extremely unlikely" as a cause.
But there are myriad different ideas about the origin of the virus including a series of conspiracy theories.
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"We must take hypotheses about both natural and laboratory spillovers seriously until we have sufficient data," the scientists said, adding that an intellectually rigorous and dispassionate investigation needed to take place.
"In this time of unfortunate anti-Asian sentiment in some countries, we note that at the beginning of the pandemic, it was Chinese doctors, scientists, journalists, and citizens who shared with the world crucial information about the spread of the virus—often at great personal cost."
China has always rejected claims that coronavirus originated in a lab and says that although Wuhan is where the first cluster of cases was detected, it is not necessarily where the virus originated.
State media has claimed that the virus may have arrived in Wuhan on frozen food imports.
Former US president Donald Trump said in April last year that he had seen evidence it had come from a laboratory in China.
But health experts and intelligence communities have previously said it is more likely that COVID-19 was naturally occurring, rather than man-made.
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