The National Institutes of Health is now admitting to funding gain-of-function research on bats infected with coronaviruses at a lab in Wuhan, China despite repeated denials from Dr. Anthony Fauci that U.S. tax dollars were used on the funding.

In a letter to Rep. James Comer, ranking member of the House Committee on Oversight and Reform, an NIH official admits that a "limited experiment" was conducted in order to test if "spike proteins from naturally occurring bat coronaviruses circulating in China were capable of binding to the human ACE2 receptor in a mouse model." 

The letter states that the laboratory mice infected with the modified bat virus "became sicker" than mice that were given the unmodified bat virus.

(Photo by J. SCOTT APPLEWHITE/POOL/AFP via Getty Images)

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, responds to questions by Senator Rand Paul during the Senate Health, Education, Labor, and Pensions Committee hearing on Capitol Hill in Washington, DC on July 20, 2021. (Photo by J. Scott Applewhite / POOL / AFP) (Photo by J. SCOTT APPLEWHITE/POOL/AFP via Getty Images)  ((Photo by J. SCOTT APPLEWHITE/POOL/AFP via Getty Images))

FAUCI RESISTED TRUMP DIRECTIVE TO CANCEL VIRUS RESEARCH GRANT LINKED TO WUHAN LAB: BOOK

The official, Lawrence A. Tabak, accused the New York City-based nonprofit EcoHealth Alliance, who funneled funds to the Wuhan lab, of not being transparent about the work that was taking place.

Gain-of-function research involves extracting viruses from animals to artificially engineer in a laboratory to make them more transmissible and deadly to humans.

GOP REPS SEEK ANSWERS FROM FAUCI ON WHETHER HE MISLED AMERICANS ON GAIN-OF-FUNCTION RESEARCH IN CHINA

Fauci, the director of the National Institute of Allergy and Infectious Diseases, has repeatedly denied any NIH money went to such research in Wuhan, but his organization has given millions of dollars in grant money to the EcoHealth Alliance which funneled at least $600,000 to Wuhan coronavirus research.

Fauci has testified before Congress stating multiple times that NIH does not fund gain-of-function research in Wuhan, but Paul has insisted that Fauci is lying to Congress and even requested a criminal referral from the Department of Justice. 

WASHINGTON, DC - MAY 11: U.S. Sen. Rand Paul (R-KY) questions Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, during a Senate Health, Education, Labor and Pensions Committee hearing to discuss the ongoing federal response to COVID-19 on May 11, 2021 in Washington, DC. (Photo by Greg Nash-Pool/Getty Images)

WASHINGTON, DC - MAY 11: U.S. Sen. Rand Paul (R-KY) questions Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, during a Senate Health, Education, Labor and Pensions Committee hearing to discuss the ongoing federal response to COVID-19 on May 11, 2021 in Washington, DC. (Photo by Greg Nash-Pool/Getty Images) (Greg Nash-Pool/Getty Images)

FAUCI ALLEGEDLY MISLED TRUMP ADMINISTRATION ON GAIN-OF-FUNCTION RESEARCH IN WUHAN: BOOK

In his questioning of Fauci at a Senate hearing this summer, Paul cited a paper on research about bat coronaviruses and said that U.S. money had essentially gone to the hazardous and controversial research – an assertion Fauci strongly objected to. 

"I have never lied before the Congress, and I do not retract that statement," Fauci said when pressed by Paul on previous testimony from the doctor that the U.S. did not fund gain of function research in Wuhan. "You do not know what you are talking about quite frankly, and I want to say that officially."

Pau responded to the news on Twitter saying that "I told you so doesn’t even begin to cover it here."

A new book from an investigative Australian reporter says that Fauci reportedly misled the Trump administration on gain-of-function research in China.

"Fauci’s public persona as a cautious, careful medical professional is contradicted by his central role in kickstarting exceptionally fraught gain-of-function research in the United States after the ban introduced in the Obama era, along with his role in funding coronavirus research in China in unsafe laboratories. Laboratories that intelligence agencies suspect may have sparked the pandemic," Sharri Markson details in her new book, "What Really Happened In Wuhan." 

In September, leaked documents obtained by private research group DRASTIC "completely contradict" claims made by both China and Fauci about the reality of gain-of-function research being done inside the Wuhan Institute of Virology that may have caused the coronavirus pandemic, according to a former State Department COVID-19 investigator.

WUHAN, CHINA - FEBRUARY 23 2017: Virologist Shi Zheng-li, left, works with her colleague in the P4 lab of Wuhan Institute of Virology (WIV) in Wuhan in central China's Hubei province Thursday, Feb. 23, 2017.- PHOTOGRAPH BY Feature China / Barcroft Studios / Future Publishing (Photo credit should read Feature China/Barcroft Media via Getty Images)

WUHAN, CHINA - FEBRUARY 23 2017: Virologist Shi Zheng-li, left, works with her colleague in the P4 lab of Wuhan Institute of Virology (WIV) in Wuhan in central China's Hubei province Thursday, Feb. 23, 2017.- PHOTOGRAPH BY Feature China / Barcroft Studios / Future Publishing (Photo credit should read Feature China/Barcroft Media via Getty Images)

On "The Story", host Martha MacCallum reported the documents released by DRASTIC revealed a plan to create a coronavirus– in this case SARS-CoV-2 – that would be more infectious to and transmissible via humans. The virus would then be released in batcaves where researchers would test the flying mammals with vaccines to see if they could cure the virus.

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Fauci's NIAID told Fox News in a statement that the doctor has been "entirely truthful."

"Gain of function is a broad term," the statement said. "The research that requires increased oversight under the HHS P3CO Framework is that which is reasonably anticipated to create, transfer or use potential pandemic pathogens resulting from the enhancement of a pathogen’s transmissibility and/or virulence in humans (ePPP). Drs. Collins and Fauci have made clear in numerous public appearances that the research in question did not fit this definition, and nothing in the last research progress report changes that fact."

The statement continues, "To be clear analysis of the published genomic data and documents from the grantee demonstrates that the naturally occurring bat coronaviruses studied under the NIH grant to EcoHealth Alliance are genetically far distant from SARS-CoV-2 and could not possibly have caused the COVID-19 pandemic. Any claims to the contrary are demonstrably false. These viruses are as genetically different from each other as humans are from cows."

"The experiment described in the final progress report provided by EcoHealth Alliance was testing to see if spike proteins from naturally occurring bat coronaviruses circulating in China were capable of binding to the human ACE2 receptor in a mouse model. This research aimed to advance our understanding of the interactions of the spike protein with the ACE2 receptor, one component of human biology, in viral infection. Importantly, the presence of the human receptor alone is not sufficient to drive human infection. All other aspects of the mice, including the immune system, remained unchanged in this model. In this limited experiment, a small number of laboratory mice infected with three experimental bat coronaviruses became sicker than those infected with WIV1, though as expected WIV1 also made the mice sick."

"The research plan for the grant was reviewed in advance of funding and was determined to be scientifically meritorious. The proposed research was also determined not to meet the definition of enhanced potential pandemic pathogen (ePPP) research because the bat coronaviruses used in this research have not been shown to infect humans and the experiments were not reasonably expected to increase transmissibility or virulence in humans. Therefore, the research was not subject to higher level review under the HHS P3CO Framework. While the findings of this limited experiment in mice were somewhat unexpected, NIAID reviewed the progress report and has determined that the research described in the progress report would not have triggered a review under the HHS P3CO Framework because the bat coronaviruses used in this research have not been shown to infect humans and the experiments were not reasonably expected to increase transmissibility or virulence in humans."

Fox News’ Marisa Schultz, Charles Creitz and Emma Colton contributed to this report