A group of scientists on Monday wrote in a letter published in The Lancet medical journal that the laboratory leak theory of COVID-19's origins is "without scientifically validated evidence."
"We believe the strongest clue from new, credible, and peer-reviewed evidence in the scientific literature is that the virus evolved in nature," the group wrote.
The letter was written by the same group of experts that published a letter in The Lancet in February 2020, at the beginning of the pandemic, saying: "We stand together to strongly condemn conspiracy theories suggesting that COVID-19 does not have a natural origin."
The authors include Peter Daszak, a member of the World Health Organization-convened team that investigated the origins of the virus. He has also worked with the lab at the center of the lab leak theory, the Wuhan Institute of Virology, as president of the EcoHealth Alliance. This has led conservative critics of Daszak to say he is too close to China.
While saying the lab leak theory lacks evidence, the letter from the scientists on Tuesday does call for further inquiry.
"WHO's report from March, 2021, must be considered the beginning rather than the end of an inquiry, and we strongly support the G7 leaders' call for 'a timely, transparent, expert-led, and science-based WHO-convened phase 2 COVID-19 origins study,' " the letter states.
The lab leak theory has grown in credibility in recent months, and President BidenJoe BidenTrump endorses challenger in Michigan AG race On The Money: Democrats get to the hard part Health Care — GOP attorneys general warn of legal battle over Biden's vaccine mandate MORE in May ordered the intelligence community to "redouble" efforts to look into the origins of the virus, including the possibility of a lab leak.
Still, there is no definitive evidence either way.
Other groups of experts have put more stock in the lab leak theory than the authors of The Lancet letter.
A letter from experts in the journal Science in May said: "Theories of accidental release from a lab and zoonotic spillover both remain viable."
The Lancet letter authors called for calm and taking the time for more scientific inquiry into the origins.
"It is time to turn down the heat of the rhetoric and turn up the light of scientific inquiry if we are to be better prepared to stem the next pandemic, whenever it comes and wherever it begins," they wrote.