British health authorities said Wednesday that they had approved the vaccine and that it would begin distribution immediately.
The US must wait until 10 December for the US Food and Drug Administration to meet and discuss the drug's emergency authorisation.
Once the drug has been approved, it will take five days before the first doses are distributed.
Both Pfizer and Moderna's upcoming vaccines have been praised by the health and science communities as effective and safe, but the FDA said in a statement that it wanted to take the time to examine the data before granting its approval.
Stephen Hahn, the head of the FDA, said that the agency planned to pour over the vaccines' raw data first.
According to Axios, the FDA head was summoned to the White House by Chief of Staff Mark Meadows to explain why the agency was not moving faster to approve the drugs.
“Let me be clear — our career scientists have to make the decision and they will take the time that’s needed to make the right call on this important decision,” Mr Hahn said in a statement.
During the meeting, Mr Meadows reportedly asked Mr Hahn why he had been working remotely from North Carolina in mid-November. He was implying that Mr Hahn had taken a vacation just as the vaccines were ready to be approved.
However, Mr Hahn said he was not in North Carolina vacationing, but was instead quarantining after being exposed to Covid-19.
Mr Hahn's spokesman, Michael Felberbaum, told CNBC that the agency head had "recently quarantined out of an abundance of caution following a potential exposure to Covid-19 while working at the FDA's White Oak campus."
“Dr. Hahn chose a remote location to quarantine and he continued working, as he has done throughout the pandemic,” Mr Felberbaum said. “The agency followed its contact tracing and notification protocols, following CDC guidelines, for the very small number of other potentially impacted employees.”
Mr Meadows is not Mr Hahn's only critic in the White House. Earlier this year, Donald Trump claimed - without evidence - that there was a deliberate attempt to slow the approval of the vaccine in order to hurt his reelection chances.
“The deep state, or whoever, over at the FDA is making it very difficult for drug companies to get people in order to test the vaccines and therapeutics,” Mr Trump tweeted on 22 August. “Obviously, they are hoping to delay the answer until after November 3rd. Must focus on speed, and saving lives!”
Even if the FDA rushed its approval of the drugs, however, the agencies working to distribute and administer the drugs would still need to find an effective way of convincing skeptical Americans that its safe.
Initial results suggest that Pfizer's vaccine is 95 per cent effective and Moderna's is 94 per cent effective. Despite those high numbers and general praise from the health and science community, some Americans are still wary of taking the drug.
In a recent Pew Research Centre survey, only 51 per cent of US adults said they would be willing to take a coronavirus vaccine. Distrust of the vaccine is higher in communities of colour, as the US has in the past used state-run health services to pressure women into sterlisation procedures.
According to Pew, only 19 per cent of the adults polled had a high level of confidence that the vaccine would yield a safe and effective product.
Dr Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases and the White House's top coronavirus doctor, has called on Americans to get the vaccine to help stop the spread of the virus. Dr Fauci said an "overwhelming majority" of Americans would have to agree to be vaccinated in order for the vaccine to be effective.
During an interview with Facebook CEO Mark Zuckerberg, Dr Fauci said he hopes at least 75 to 85 per cent of Americans take the vaccine.
"If we get to that point, Mark...by the end of second quarter of the year you can have enough protection in this country that the pandemic as we know it will be well, well suppressed below the danger point," Dr Fauci said.
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