Donald Trump described Dr Anthony Fauci and Dr Deborah Birx as 'two self-promoters trying to reinvent history' on Monday as he accused the pair of being excessively cautious and medically misguided, insisting that his decisions to overrule them 'is saving the entire world'.

The former president said Fauci was inconsistent, describing him as 'the king of "flip flops",' and denied Birx's claim that they had a 'very difficult' phone call at the start of the pandemic, when she told him how severe a threat the pandemic posed.

'She was a very negative voice who didn't have the right answers,' Trump said.

His stinging statement came after Fauci and Birx both appeared on CNN on Sunday, with Birx speaking of her regrets as White House COVID task force chief, and Fauci appearing to claim credit for the decision to quickly develop vaccines against COVID-19.

Fauci, the director of the National Institute of Allergy and Infectious Diseases, made the comment in an interview with CNN for a special, diving into the details of America's pandemic response.

'When I saw what happened in New York City, almost over-running of our healthcare systems, and that's when it became very clear that the decision we made on January 10 to go all out and develop a vaccine, may have been the best decision that I've ever made with regard to intervention as the director of the institute,' Fauci said.

Fauci's remarks seemed to gloss over the key role played by pharmaceutical companies and Operation Warp Speed - the Trump administration's program to manufacture, test and deliver vaccines to the public in record time.

Trump on Monday described Fauci and Birx as bumbling failures.

Fauci, he said, 'tried to take credit for the vaccine, when in fact he said it would take three to five years'.

Trump said it was his decision to begin the vaccine program.

'We developed American vaccines by an American President in record time, nine months, which is saving the entire world,' he said.

'We bought billions of dollars of these vaccines on a calculated bet that they would work, perhaps the most important bet in the history of the world.'

The former president said Fauci was 'incapable' of pushing the Food and Drug Administration (FDA) to hurry with their approval process, and accused him of constantly changing his advice.

'Dr Fauci is also the king of "flip flops" and moving the goalposts to make himself look as good as possible,' Trump said.

He said that Fauci had argued against Trump's decision to end incoming flights from China, and pointed out that in the early days of the pandemic Fauci recommended not wearing a face mask.

Trump concluded: 'I was the one to get it done, and even the fake news media knows and reports this.'

He also mocked Fauci's ceremonial first pitch at the opening game of the baseball season in July, ridiculing the lifelong baseball fan for talking about his sporting prowess as a young man.

The former president then turned to Birx, who was the head of his White House COVID task force.

Birx appeared on the same show as Fauci on Sunday night, and in recent weeks has given numerous interviews in which she has expressed regret for how she handled her role as head of the White House coronavirus task force.

'Dr. Birx is a proven liar with very little credibility left,' Trump said, claiming that Fauci would talk badly about her behind her back.

'The States who followed her lead, like California, had worse outcomes on Covid, and ruined the lives of countless children because they couldn’t go to school, ruined many businesses, and an untold number of Americans who were killed by the lockdowns themselves.

'Dr. Birx was a terrible medical advisor, which is why I seldom followed her advice.'

The former president also swiped at Birx for traveling for Thanksgiving to see her family despite emphasizing guidance to avoid nonessential travel.

Trump delivered the criticism despite traveling frequently for campaign events throughout the pandemic, including holding a host of largely maskless rallies in the weeks leading up to the election.

Trump's anger at his former health officials has been growing.

In a formal statement earlier this month, Trump said: 'I hope everyone remembers when they're getting the COVID-19 (often referred to as the China Virus) Vaccine, that if I wasn't president, you wouldn't be getting that beautiful 'shot' for 5 years, at best, and probably wouldn't be getting it at all.'

'I hope everyone remembers!' he added.

Indeed, Trump has often accused Fauci of nay-saying, pointing to statements Fauci made early in the pandemic that vaccines typically take years to develop.

Jason Miller, a close advisor to Trump, responded to a DailyMail.com article about Fauci's vaccine remark with scorn, tweeting: 'If it were up to Fauci we still wouldn't have a Covid vaccine.'

Operation Warp Speed was a public-private partnership initiated by the Trump administration to facilitate and accelerate the development of COVID vaccines.

Fauci was one of the lead members of Trump's Coronavirus Task Force, and President Joe Biden subsequently appointed him as chief medical advisor. He had no formal role in Operation Warp Speed.

Fauci has never been publicly named as a key figure in the development of vaccines or in Operation Warp Speed, which operated separately from the Coronavirus Task Force.

Throughout the pandemic, Fauci has been eager to give interviews, seeming to revel in the title 'America's Doctor' that the media bestowed on him.

Like Fauci, CNN Chief Medical Correspondent Dr. Sanjay Gupta seemed to overlook the role that Operation Warp Speed and pharmaceutical companies played in the development of the vaccines.

'The life-saving and record-breaking vaccines that Dr. Fauci oversaw were a giant success for 'The Doctors' and for science and for the world,' Gupta said in a voiceover for the special.

The CNN special featured interviews with six medical doctors who played key roles in America's pandemic response, including Fauci, Dr. Deborah Birx, Dr. Robert Kadlec, Dr. Robert Redfield, Dr. Stephen Hahn and Dr. Brett Giroir.

In interview clips from the show that were previously released, Redfield, the former head of the Centers for Disease Control and Prevention, made headlines by saying he believes the virus that causes COVID-19 escaped from Wuhan lab in China and may have been circling as early as September 2019.

In the documentary on Sunday, he expounded on this opinion, saying he believes a lab accident is the most likely origin of the virus.

It is the first time Redfield, who was appointed CDC director by Trump, has stated publicly that he believes COVID-19 originated in a lab and not in a wet market where linked to an initial cluster of cases.

'I'm of the point of view that I still think the most likely etiology of this pathogen in Wuhan was from a laboratory... escaped. Other people don't believe that, that's fine. Science will eventually figure it out,' he said.

'It's not unusual for respiratory pathogens that are being worked on in laboratories to infect the laboratory worker.

'That's not implying any intentionality. It's my opinion, right? But I am a virologist. I have spent my life in virology.'

China has strenuously insisted that the pandemic started when COVID-19 jumped from a bat to a human or through an intermediary species at a wet market in Wuhan.

Redfield, however, says that explanation doesn't make 'biological sense' to him.

'I do not believe this somehow came from a bat to a human and at that moment in time the virus came to the human, became one of the most infectious viruses that we know in humanity for human-to-human transmission,' he said.

'Normally, when a pathogen goes from a zoonotic to human, it takes a while for it to figure out how to become more and more efficient.'

He believes it started in a lab that was already studying the virus, which would mean COVID-19 was being exposed to human cell cultures.

'Most of us in a lab, when trying to grow a virus, we try to help make it grow better, and better, and better, and better, and better, and better so we can do experiments and figure out about it. That's the way I put it together.'

Redfield also said he believes the virus started circulating in Wuhan as early as September 2019, which is several months earlier than the official timeline.

In a separate interview, Fauci dismissed Redfield's theory, saying that if the virus circulated for months before spreading widely, it suggested a direct transmission from animals to humans.

Elsewhere in the CNN special, titled 'COVID WAR: The Pandemic Doctors Speak Out,' Birx said number of coronavirus deaths in the US would have 'decreased substantially' if cities and states had learned from the first surge that claimed 100,000 lives.

She claimed subsequent surges could have been 'mitigated' if the lessons had been learned and acted on.

Birx led the Trump administration's Coronavirus Task Force, but announced her intent to retire from government after it emerged that she had hosted three generations of her family from two households over Thanksgiving, despite her own warnings to Americans to restrict such gatherings to 'your immediate household'.

'I look at it this way. The first time we have an excuse,' Birx said of the initial surge of cases and deaths last spring.

'There were about a hundred thousand deaths that came from that original surge. All of the rest of them, in my mind, could have been mitigated or decreased substantially.'

Birx also revealed that she had a 'very uncomfortable' phone call with Trump in August after she warned the press about the severity of the pandemic.

'It was a CNN report in August that got horrible pushback,' Birx told said. 'That was a very difficult time, because everybody in the White House was upset with that interview and the clarity that I brought about the epidemic,' she continued.

'I got called by the President,' Birx detailed. 'It was very uncomfortable, very direct and very difficult to hear.'

Birx deflected when CNN correspondent Gupta asked if Trump threatened her during the call.

'I would say it was a very uncomfortable conversation,' she reiterated.