This casts serious doubts over next week’s planned event. The Democratic campaign had said that its candidate would participate. “Vice President Biden looks forward to speaking directly to the American people,” deputy campaign manager Kate Bedingfield said in a statement.

It is more evidence that the race remains defined by the virus, even as Trump has attempted to underplay it.

Trump was diagnosed with the coronavirus a week ago. However, on Tuesday he said he looked forward to debating Biden on stage in Miami. “It will be great!” he tweeted.

Biden, for his part, said he and Trump “shouldn’t have a debate” as long as the president remains COVID-positive.

Biden told reporters in Pennsylvania that he was “looking forward to being able to debate him” but said “we’re going to have to follow very strict guidelines.”

Trump was pronounced ill with the virus just 48 hours after debating Biden in person for the first time in Cleveland.

While the two candidates remained a few metres apart during the debate, Trump’s infection sparked health concerns for Biden and sent him to undergo multiple COVID-19 tests before returning to the campaign trail.

Trump was still contagious with the virus when he was discharged from Walter Reed National Military Medical Center on Monday but his doctors have not provided any detailed update on his status.

According to the Centers for Disease Control and Prevention, those with mild to moderate symptoms of COVID-19 can be contagious for as many as 10 days — and should isolate for at least as long.

The first debate between the two candidates last week was an ugly affair, marked by insults and constant interruptions. Trump in particular repeatedly talked over his rival, leading Biden to comment that it was hard to keep up with the president’s ranting.

It’s not the first debate in which the candidates are not in the same room. In 1960, the third presidential debate between Richard Nixon and John F. Kennedy was broadcast with the two candidates on opposite coasts.