WASHINGTON (AP) — Dr. Anthony Fauci, the top U.S. infectious disease expert until leaving the government in 2022, faced heated questioning Monday from Republican lawmakers about the origins of the COVID-19 pandemic.

A Republican-led subcommittee has spent over a year probing the nation's response to the pandemic and whether U.S.-funded research in China may have played any role in how it started. Democrats opened the hearing saying the investigation so far has found no evidence that Fauci did anything wrong while missing an important opportunity to prepare for the next scary outbreak.

Fauci – alternately a trusted voice during the pandemic and the target of partisan attacks, even death threats – spent 14 hours over two days in January being grilled by the House panel behind closed doors. On Monday, they questioned him again, in public and on camera for the first time since he ended more than five decades of government service.

This time around he faced a new set of questions about the credibility of his former agency, the National Institutes of Health. Last month, the House panel revealed emails from an NIH colleague about ways to evade public records laws, including by not discussing controversial issues on government email.

The main issue: Many scientists believe the virus most likely emerged in nature and jumped from animals to people, probably at a wildlife market in Wuhan, the city where the outbreak began. There's no new scientific information supporting that the virus might instead have leaked from a laboratory. A U.S. intelligence analysis says there's insufficient evidence to prove either way -- and a recent Associated Press investigation found the Chinese government froze critical efforts to trace the source of the virus in the first weeks of the outbreak.

Fauci has long said publicly that he was open to both theories but that there's more evidence supporting COVID-19's natural origins, the way other deadly viruses including coronavirus cousins SARS and MERS jumped into people.

"I have repeatedly stated that I have a completely open mind to either possibility and that if definitive evidence becomes available to validate or refute either theory, I will ready accept it," he said in an opening statement for Monday's hearing.

Republicans also have accused Fauci of lying to Congress when he denied in May 2022 that his agency funded "gain of function" research – the practicing of enhancing a virus in a lab to study its potential real-world impact – at a lab in Wuhan.

NIH for years gave grants to a New York nonprofit called EcoHealth Alliance that used some of the funds to work with a Chinese lab studying coronaviruses commonly carried by bats. Last month, the government suspended federal funding to EcoHealth Alliance – and proposed barring it from future funding – citing its failure to properly monitor some of those experiments.

The definition of "gain of function" covers both general research and especially risky experiments to "enhance" the ability of potentially pandemic pathogens to spread or cause severe disease in humans. In transcripts of Fauci's January interviews with the House panel, he stressed he was using the risky experiment definition.

"It would be molecularly impossible" for the bat viruses studied with EcoHealth's funds to be turned into the virus that caused the pandemic, he reiterated in Monday's opening statement.

As for hiding public records, Fauci said in the opening remarks that "to the best of my knowledge I have never conducted official business via my personal email."

Fauci became a household name in the pandemic – first under President Donald Trump and later as a chief adviser to President Joe Biden -- trying to explain the latest public health advice to a frightened public even as scientists were struggling to learn about the new virus. Research from the agency he led for 38 years, NIH's National Institute on Allergy and Infectious Diseases, led to vaccines that allowed a return to normalcy.

The House panel also questioned him about the science behind some controversial advice, including social distancing.

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