The US continued its push to investigate the origins of the COVID-19 pandemic on Thursday, after President Joe Biden ordered intelligence agencies to look into the origins again.

The US State Department, which ended a Trump-era probe into the theory that the virus leaked from a Wuhan, China lab, said it would continue to cooperate with other government agencies and pushed China to work with outside investigations.

The other main theory was that the illness spread from bats to humans via another, currently unknown species. The World Health Organization (WHO), in a research trip to Wuhan earlier this year, had said that a "lab leak" appeared "extremely unlikely."

"China's position that their part in this investigation is complete is disappointing and at odds with the rest of the international community that is working collaboratively across the board to bring an end to this pandemic and improve global health security," said State Department spokesman Ned Price.

Dr. Anthony Fauci, a White House coronavirus adviser, said on Wednesday that he and other scientists "believe that the most likely scenario is that this was a natural occurrence, but no one knows that 100% for sure."

"And since there's a lot of concern, a lot of speculation and since no one absolutely knows that, I believe we do need the kind of investigation where there's open transparency and all the information that's available, to be made available, to scrutinize," said Fauci at a Senate hearing.

The US Senate on Wednesday approved two Wuhan lab-related amendments to a mostly unrelated bill that would increase US investments in innovation. The amendments were passed without opposition. One of the amendments, introduced by Kentucky Republican Rand Paul, would block the US from funding Chinese projects looking into increasing the severity or transmissibility of a virus. The other amendment, from Iowa Republican Joni Ernst, would prevent funding for the Wuhan Institute of Virology, the lab in question.

International response

Canadian Prime Minister Justin Trudeau supported the US decision to further investigate the pandemic's origins.

"I know there are a lot of theories out there, but we need to make sure we're getting to a full and complete airing of the facts to actually understand what happened and how to make sure it never happens again," said Trudeau.

China responded by accusing the Biden administration of playing politics and skirting its responsibility in calling for a new investigation. Chinese Foreign Ministry spokesperson Zhao Lijian said Biden's order proved the US "does not care about facts and truth, nor is it interested in serious scientific origin tracing."

He also suggested that the pandemic could have spread from a US military laboratory.

"There are many doubts about the lab at Fort Detrick — and the US has more than 200 biological laboratories in the world," said Lijian, referencing a military base in the US state of Maryland.

The Chinese Embassy in Washington accused political forces of focusing on a blame game. A statement on the embassy's website on Wednesday did not specifically mention Biden's demand.

"Smear campaign and blame shifting are making a comeback, and the conspiracy theory of 'lab leak' is resurfacing," said the embassy.

Facebook changing course

Social media site Facebook said it would no longer ban posts suggesting the COVID-19 pandemic began after it escaped from the laboratory in Wuhan, China lab.

The decision came late Wednesday. Facebook said in a statement they were "continuing to work with health experts to keep pace with the evolving nature of the pandemic and regularly update our policies as new facts and trends emerge."

Evelyn Douek, a Harvard University lecturer discussed the potential ramifications on Twitter. "Another exhibit for the possibility that there will be a swing back against the more heavy-handed moderation as more comes out about what [people] got wrong and where contestation was important," said Douek.

Deliberate leak unlikely, says infectious diseases expert

DW spoke to William Schaffner, professor of preventive medicine and infectious diseases at the Vanderbilt University Medical Center, about the probable source of the coronavirus.

Schnaffer said although "laboratory accidents do occur" he was still of the belief that "Mother Nature" was more likely to be responsible, before adding, "but I have colleagues who are more suspicious about laboratory accidents."

Asked about the prospect of a deliberate leak, Schaffner was far more skeptical, however. 

"This would have been a very dumb agent for a country to use as bio warfare, because you shoot yourself in the foot, it blows back on your own people. You cannot control a respiratory virus and one that's so easily transmitted. So I don't think anybody who makes a bio warfare weapon would choose a coronavirus because you can't control it."

kbd, jsi/msh (AP, dpa, AFP)