Origins of Covid-19 need to be investigated further, leading scientists say

The origin of the novel coronavirus is still unclear and there is not yet enough evidence to say conclusively if it occurred naturally or was caused by a laboratory leak, a group of senior scientists said in a letter.

"More investigation is still needed to determine the origin of the pandemic," said the 18 scientists, 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.

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"Theories of accidental release from a lab and zoonotic spillover both remain viable," the scientists said in a letter to the journal Science.

The Covid-19 pandemic has killed 3.34 million people worldwide since it emerged in China in late 2019.