Only hours earlier, speaking to Fox News, Trump had said a vaccine could come in “four weeks, it could be eight weeks”.

Democrats have expressed concern that Trump is putting political pressure on government health regulators and scientists to approve a rushed vaccine in time to help turn around his uphill bid for re-election against challenger Joe Biden on November 3.

Experts including top US government infectious diseases doctor Anthony Fauci say vaccine approval is more likely toward the end of the year.

At the ABC town hall Trump was asked why he’d played down the gravity of the Covid-19 pandemic, which has now killed close to 200,000 people in the US.

Trump replied by saying: “I didn’t downplay it. I actually, in many ways, I up-played it in terms of action.”

But Trump himself told journalist Bob Woodward during taped interviews for the new book Rage – published Tuesday – that he had deliberately decided to “play it down” to avoid alarming Americans.

Returning to one of his most controversial views on the virus, that has ravaged the economy and which government scientists say will remain a danger for some time, Trump insisted “it is going to disappear”.

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“It would go away without the vaccine but it’s going to go away a lot faster with it,” he said.

Challenged about how the virus would go away by itself, he said “you’ll develop like a herd mentality”. apparently meaning the concept of herd immunity, when enough people have developed resistance to the disease to effectively stop transmission.

“It’s going to be herd developed and that’s going to happen. That will all happen but with a vaccine, I think it will go away very quickly. But I really believe we’re rounding the corner,” he said.

The president, who is rarely seen wearing a mask in public and long refused to push Americans to adopt the habit, said “a lot of people don’t want to wear masks and people don’t think masks are good”.

Asked what people he meant, Trump answered: “Waiters”.

“They come over and they serve you and they have a mask,” he said. “I saw it the other day when they were serving me and they’re playing with the mask. I’m not blaming them. I’m just saying what happens: They’re playing with the mask. So the mask is over, and they’re touching it, and then they’re touching the plate, and that can’t be good.”

Polls show that a majority of Americans disapprove of Trump’s handling of the health crisis.

The latest NBC News|SurveyMonkey Weekly Tracking poll Tuesday found that 52 per cent of adults do not trust Trump’s statements about an upcoming coronavirus vaccine, compared to 26 per cent who do.

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Trump has faced criticism for holding large-scale campaign events in Nevada and other states – events that his adviser Fauci has described as “absolutely” risky.

His Democratic challenger, former vice-president Joe Biden, last week accused Trump of “dereliction” of duty in dealing with the pandemic, which has cost millions of jobs.

The United States has reported 6.6 million cases of Covid-19, the disease caused by the virus, the highest number worldwide, and more than 195,000 deaths. That accounts for 20 per cent of the cases worldwide, although the United States has just 4 per cent of the world’s population

Trump said the United States had a number of cases because it did more testing that other countries.

Additional reporting by Reuters and Business Insider