The origin of the novel coronavirus is still unclear and the theory that it was caused by a laboratory leak needs to be taken seriously until there is a rigorous data-led investigation that proves it wrong, a group of leading scientists said.

Covid-19, which emerged in China in late 2019, has killed 3.34 million people, cost the world trillions of dollars 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 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 Centre...