Former CDC Director Robert Redfield told CNN on Friday that he believes the coronavirus "escaped" from the Wuhan Institute of Virology, and that it was spreading as early as September or October of 2019 — though he stressed that it was his "opinion."

Why it matters: It's a stunning assertion, offered with little evidence, by the man who led the U.S. government's public health agency from the time the virus was first detected in Wuhan through the entirety of the Trump administration's response.

The big picture: The debate over the origins of the coronavirus has been ongoing since the start of the pandemic, causing rising tensions between the U.S. and China — especially during the presidency of Donald Trump, who frequently accused the Chinese government of "unleashing" a "plague" on the world.

• The Wuhan Institute of Virology is the only facility in China permitted to handle the most dangerous known pathogens, and is located just under nine miles from the wet market where some scientists say the outbreak may have originated.
• A World Health Organization team that traveled to Wuhan to investigate the origins of COVID-19 said it is "extremely unlikely" the virus came from a laboratory accident, and that it most likely jumped to humans via an intermediate species.
• However, China refused to provide the WHO team with raw data about the first cases detected in Wuhan, leading the Biden administration to issue a statement expressing "deep concerns" about the investigation and demanding transparency from Beijing.

What they're saying: "I'm of the point of view that I still think the most likely etiology of this pathology in Wuhan was from a laboratory. Escaped. Other people don't believe that. That's fine. Science will eventually figure it out," Redfield told CNN's Sanjay Gupta.

• "It's not unusual for respiratory pathogens that are being worked on in a laboratory to infect the laboratory worker. ... That's not implying any intentionality. It's my opinion, right? But I am a virologist. I have spent my life in virology," he continued.
• "I do not believe this somehow came from a bat to a human and at that moment in time that the virus came to the human, became one of the most infectious viruses that we know in humanity for human-to-human transmission."

Between the lines: Lab accidents in the U.S. are not especially rare, as USA Today's Alison Young noted in a recent opinion piece arguing why the Wuhan lab theory cannot be ruled out. The CDC itself experienced a possible contamination in a lab where it was making COVID-19 test kits early in the pandemic.

What to watch: The WHO team is expected to soon publish a 300-page final report on its investigation, after scrapping plans for an interim report amid mounting tensions between the U.S. and China.