Washington (AFP)

Long dismissed out of hand by most experts, deemed highly improbable if not far-fetched, the theory of the laboratory accident to explain the origin of Covid-19 has come back in force in recent weeks in the American debate.

"The list of people supporting the thesis of an animal origin has not moved. And that of people suggesting that (the virus) may have come out of a laboratory continued to grow," Scott summed up Monday on CNBC Gottlieb, a respected former boss of the United States Drugs Agency (FDA).

"A year ago," supporting the animal thesis "made a lot of sense because it was the most likely scenario," he explained.

But what is called "the intermediate host", that is, the animal from which the virus was transmitted to humans, has still not been discovered.

"And it's not for lack of looking."

“The question, for many people, is, when do the coincidences get too many?” He asked, pointing to the growing body of “circumstantial evidence”.

On Sunday, the Wall Street Journal claimed to have had access to unpublished US intelligence information, reporting that three researchers at the Wuhan Institute of Virology in China had suffered as early as November 2019 from "symptoms compatible with both those of Covid-19 and seasonal infection ".

China revealed the existence of an outbreak of pneumonia cases in Wuhan at the end of December, the following month, to the World Health Organization (WHO).

Beijing has denied the Wall Street Journal information, calling it "totally false".

- Calls from the scientific community -

After a four-week stay in Wuhan earlier this year, a joint study by experts from the World Health Organization (WHO) and China ruled in March "extremely unlikely" a laboratory incident.

But the boss of the WHO himself, Tedros Adhanom Ghebreyesus, had called for a new investigation into the hypothesis of the laboratory leak.

Several countries, including the United States, had expressed their "concerns" and called on China to give "full access" to its data.

A request renewed on Monday on the occasion of the 74th World Health Assembly.

And calls for further investigation are growing, including within the scientific community.

In mid-May, around fifteen experts published an article in the prestigious journal Science: "We need more research to determine the origin of the pandemic", they claimed.

Theories of animal or accidental origin in the laboratory "both remain viable", they wrote, but "they have not been given fair consideration."

Both theories "must be seriously considered until we have enough data," they said, asking "public health agencies and research laboratories to open their data to the public."

Determining how the virus, which has claimed more than 3.4 million lives worldwide, passed to humans is considered crucial in trying to prevent the next pandemic.

- Trump triumphant -

In the United States, the hypothesis of a leak of the virus from the Chinese laboratory had so far mainly been fueled by the administration of Donald Trump.

"Now everyone recognizes that I was right when I declared Wuhan very early on as the source of Covid-19," the former US president triumphed in a statement on Monday.

"To me it was obvious from the start."

However, many experts remain more cautious.

A lab accident "is a possibility that exists," Anthony Fauci, prominent immunologist and White House adviser, said two weeks ago at a Senate hearing.

The same day, during a public event, he was asked if he was certain of a natural origin of the virus: "No, I am not convinced. I think we must continue to investigate. about what happened in China until we find out, as best we can, what exactly happened, "he said.

But for Scott Gottlieb it is likely that the answer will never appear clearly: "On the assumption that (the virus) did indeed come out of a Chinese laboratory - and I do not say that it is - we will never know without a whistleblower or regime change in China, "he said.

© 2021 AFP