Earlier in the day, Fauci said the review for the U.K.'s authorization was done in a "much less deep" way than would have been done by the U.S. Food and Drug Administration.
"The U.K. has decided to do it a little bit differently, they've gone over it very quickly," he told Sky News in a video published Thursday. "And I can say, and this is not a criticism, but they've done it in a way that is much less deep than has been done and is being done by the FDA in the United States."
Fauci, director of the National Institute of Allergy and Infectious Diseases, said the FDA's reviews are a "very, very stringent process of literally point-by-point, analyzing the data." The U.S. agency "I think, everyone realizes globally is the gold standard of regulatory function," he added.
Fauci made similar remarks to Fox News and CBS.
Fauci later walked back those remarks, telling BBC television that he had faith in the U.K. regulators.
"There really has been a misunderstanding, and for that I'm sorry, and I apologize for that," Fauci said in an interview with BBC television, according to Reuters. "I do have great faith in both the scientific community and the regulatory community in the UK."
In response to Fauci's initial comments, a spokesperson for the Medicines and Healthcare products Regulatory Agency said the U.K. regulator "rigorously assessed the data in the shortest time possible, without compromising the thoroughness of our review."
"COVID-19 vaccines, including this one, are being developed in a coordinated in a way that allows some stages of this process to happen in parallel to condense the time needed, but it does not mean steps and the expected standards of safety, quality and effectiveness have been bypassed," the spokesperson said in an email.
The U.K. authorized Pfizer's vaccine with BioNtech on Wednesday, becoming the first country to do so. It will likely add pressure on the FDA to quickly do the same, especially as the White House is asking FDA Commissioner Dr. Stephen Hahn why the agency hasn't moved faster to authorize Pfizer's vaccine.
The U.S. and the U.K. review vaccines differently, however. Pfizer had been submitting data on its vaccine on a "rolling basis" to the U.K. That means regulators there were able to review the data in real time and do so until there was enough evidence to support a formal authorization. A rolling review is a tool that regulators use to speed up the assessment of promising drugs or vaccines.
In the U.S., the FDA will go through every aspect of the data submitted in the application, including reviewing all safety information "to make sure there are no cracks" and everything is "solid," said Dr. Paul Offit, a voting member of the Vaccines and Related Biological Products Advisory Committee, which is scheduled to review Pfizer's vaccine on Dec. 10.
Fauci told Sky News the FDA is "hurrying it up a bit" but "not nearly as quickly as you did in the U.K."
"If we did that in the United States, it would have been to our disadvantage because it would have generated a lot of skepticism about the speed at which it was approved," he said. "We don't look upon it as a race, who won the race. The product is there. The trial was done. The data look really good," he added.
The reluctance or refusal to get vaccinated has been a growing problem in the U.S. long before the pandemic started. Numerous polls find many Americans are skeptical about getting a Covid-19 vaccine amid escalated fears due to the pandemic and concerns that President Donald Trump is pressing regulators to approve a vaccine.
This week, former Presidents Barack Obama, George W. Bush and Bill Clinton said they will take a coronavirus vaccine once one is available and may film it to build confidence in the U.S. about vaccine safety.
Disclosure: Comcast is the parent of both Sky News and NBCUniversal's CNBC.