The possibility the Covid virus leaked from a laboratory should not be ruled out, a former top Chinese government scientist has told BBC News. As head of China's Centre for Disease Control (CDC), Prof George Gao played a key role in the pandemic response and efforts to trace its origins.

China's government dismisses any suggestion the disease may have originated in a Wuhan laboratory. But Prof Gao is less forthright.

In an interview for the BBC Radio 4 podcast Fever: The Hunt for Covid's Origin, Prof Gao says: "You can always suspect anything. That's science. Don't rule out anything."

A world-leading virologist and immunologist, Prof Gao is now vice-president of the National Natural Science Foundation of China after retiring from the CDC last year.

In a possible sign that the Chinese government may have taken the lab leak theory more seriously than its official statements suggest, Prof Gao also tells the BBC some kind of formal investigation into the Wuhan Institute of Virology (WIV) was carried out.

"The government organised something," he says, but adds that it did not involve his own department, the China CDC.

We asked him to clarify whether that meant another branch of government carried out a formal search of the WIV - one of China's top national laboratories, known to have spent years studying coronaviruses.

"Yeah," he replies, "that lab was double-checked by the experts in the field."

It's the first such acknowledgement that some kind of official investigation took place, but while Prof Gao says he has not seen the result, he has "heard" that the lab was given a clean bill of health.

"I think their conclusion is that they are following all the protocols. They haven't found [any] wrongdoing."

(Source: BBC)