US President Donald Trump addressed supporters from a White House balcony on Saturday, his first public appearance since he tested positive for COVID-19 on October 1. The White House sent out 2,000 invitations out but only few hundred people attended the event, according to US media. Photo: VCG

US President Donald Trump on Sunday declared himself immune to COVID-19 and ready for a fight as his White House race against surging rival Joe Biden enters its critical final weeks.

Trump's doctors gave him the all-clear Saturday to return to the campaign trail after he was ruled no longer a coronavirus transmission risk, and on Sunday he said while calling in to a campaign event that he tested "totally negative."

But he has yet to be declared virus-free, and his immunity claim is unproven.

"It looks like I'm immune for, I don't know, maybe a long time and maybe a short time, it could be a lifetime, nobody really knows, but I'm immune," Trump told the Fox News show "Sunday Morning Futures."

"So now you have a president who doesn't have to hide in a basement like his opponent," Trump added - in a jab at Democratic challenger Biden, who has taken a far more cautious approach to campaigning during the pandemic.

But it is not yet clear to what degree contracting COVID-19 confers immunity, with early studies suggesting a few months while newer ones have indicated it could last longer.

Twitter on Sunday hid a tweet from Trump in which he claimed he was immune, saying the post violated its rules about misleading and potentially harmful misinformation.

The tweet was still visible once users clicked through the warning.

Trump, 74, was treated with an experimental antibody cocktail made by Regeneron that may give immunity for just a few months when taken as a treatment rather than as a vaccine.

"In some cases, vaccines can last for decades. [But] if you get it in the form of natural immunity, that isn't known yet," Regeneron CEO Leonard Schleifer told CBS's "Face the Nation" on Sunday.

"If you get it in our vial, if you will, that's probably going to last you for months," he said.

Badly trailing Biden with just weeks until the November 3 vote, Trump has been counting the days until he can hit the trail again.

The Republican leader rallied hundreds of supporters for a comeback event at the White House on Saturday, and is planning back-to-back rallies this week - in Florida on Monday, then Pennsylvania and Iowa - in a bid to salvage his struggling campaign.

AFP