The Wall Street Journal editorial board wrote Thursday it was "reasonable to ask" why Dr. Anthony Fauci was slow to accept the lab-leak theory concerning the origins of the coronavirus.

The board described the infectious disease expert's correspondence on the origins of the virus and gain-of-function research, derived from the release of his emails to the public on Tuesday, as "all the more reason" there should be an investigation into the U.S. links to the Wuhan Institute of Virology (WIV).

In the early days of the pandemic, Fauci dismissed the theory that the coronavirus could have originated in a lab in Wuhan, China, at one point claiming the virus almost surely "could not have been artificially or deliberately manipulated." But he said last month he was "not convinced" the virus developed naturally. 

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"The emails, released after media freedom-of-information requests, show that Dr. Fauci followed debates about Covid-19’s origin from the beginning," the board wrote. "In early 2020, the immunologist Kristian G. Andersen wrote to him that the virus had some ‘unusual features’ hinting at manipulation in a lab setting."

"Mr. Andersen later published a paper rejecting the lab-leak theory for lack of evidence. And Dr. Fauci began sharing articles arguing in favor of a natural origin while giving advice to scientists writing about the issue," it continued. "But conclusive proof of a zoonotic origin hasn’t emerged, and it’s reasonable to ask why Dr. Fauci was slow to accept the possibility of a lab leak."

It was revealed in Fauci's emails that Peter Daszak of the EcoHealth Alliance, the non-profit that served as the intermediary for the $3.4 million given by the National Institutes of Health (NIH) to the WIV, wrote him in April 2020 to express his thanks "for publicly standing up and stating that the scientific evidence supports a natural origin." 

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"The NIH money was spent on researching bat coronaviruses, and it’s likely the WIV conducted gain-of-function research to make them more deadly or infectious," the board wrote, before explaining that, in a Feb. 2020 email, Fauci instructed a deputy to read a paper on gain-of-function research on coronaviruses, saying, "You will have tasks today that must be done." 

The deputy later responded that he would "try to determine if we have any distant ties to this work abroad."

Fauci said Wednesday he couldn't guarantee he knew everything that was going on in the WIV and that his emails "are really ripe to be taken out of context."

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"That may be true. But it’s all the more reason to investigate the U.S. links to WIV and gain-of-function research. The issue relates to Covid’s origins but also to the future risks and benefits of such research," the board wrote.