Centers for Disease Control and Prevention Director Dr. Rochelle Walensky on Wednesday did not discount that Covid-19 could have originated in a laboratory, saying it "certainly" was "one possibility."
Most coronaviruses, however, "generally come from an animal origin," Walensky said in Senate testimony after saying she had not seen enough data to give her opinion on how the current pandemic originated.
The remarks from the top Biden administration health official came amid growing calls to investigate whether the virus had zoonotic, or animal, origins or came from a lab in Wuhan, China.
The World Health Organization said in a report in March that it was "extremely unlikely" that the virus was introduced to humans through an accidental lab leak. But that conclusion has been heavily criticized, and other scientists have since come forward calling for more investigation.
"Theories of accidental release from a lab and zoonotic spillover both remain viable," said a letter from 18 scientists published in the journal Science last week. Other scientists have criticized that letter for drawing a false equivalence between the likelihood of a lab leak versus a natural-origin scenario, The New York Times reported.
The CDC's website currently says that while the exact source of the outbreak is unknown, "we know that it originally came from an animal, likely a bat."
Covid-19 was first detected in Wuhan, in the Hubei province of China.
The origin of the virus has increasingly become a hotly discussed topic in American politics as well.
In Wednesday's hearing on the CDC's budget for the next fiscal year starting Oct. 1, Sen. John Kennedy, R-La., asked Walensky for her opinion on where the pandemic started.
"I don't believe I've seen enough data, individual data for me to be able to comment on that," Walensky said.
Asked what the possibilities are, Walensky said, "Certainly the possibilities of, that most coronaviruses that we know of are of origin from, that have infected the population — SARS CoV-1, MERS — generally come from an animal origin."
Kennedy responded: "Are there any other possibilities?"
"Certainly a lab-based origin is one possibility," Walensky said.
Covid-19 grew into a pandemic in March 2020. The virus has now infected more than 164 million and killed more than 3.4 million people worldwide, according to Johns Hopkins University.
Robert Redfield, the former CDC director who worked on the U.S. response to the pandemic under ex-President Donald Trump, said in March he believes the coronavirus originated in a Wuhan lab.