Trump declares himself 'immune' to Covid-19. His doctors won't say when he last tested negative.

President Donald Trump said Sunday that he may have the "protective glow" of immunity from Covid-19, although many details about his recovery — including the date of his last negative coronavirus test — remain unknown.

In an extensive interview with Fox News' Maria Bartiromo, Trump claimed that he "beat" the coronavirus, passing the "highest standards" for proving so. Trump said he is also no longer taking any medications to combat the virus after having been placed on a heavy steroid typically given to people with more severe cases.

"It looks like I'm immune for, I don't know, maybe a long time, maybe a short time," he said. "It could be a lifetime. Nobody really knows, but I'm immune. So the president is in very good shape to fight the battles."

In two virtual rallies with supporters in the afternoon, Trump said he had "tested totally negative" and claimed that he has "fully recovered."

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As The Associated Press reported, Covid-19 reinfection is unlikely for at least three months after a person acquires the virus, but few diseases come with lifetime immunity. Researchers said in August that a Hong Kong man had been infected for a second time, suggesting that immunity may be temporary for at least some patients.

Trump's physician said in a letter Saturday that he is no longer considered a transmission risk and can now be around others safely.

"Now at day 10 from symptom onset, fever-free for well over 24 hours and all symptoms improved, the assortment of advanced diagnostic tests obtained reveal there is no longer evidence of actively replicating virus," Dr. Sean Conley said in a memo. "Moving forward, I will continue to monitor him clinically as he returns to an active schedule."

Conley added that Trump has "decreasing viral loads," meaning a lessening of how much virus is present in any sample taken from a patient.

But Conley, who admitted this month that he was providing a rosier outlook of the president's condition to convey an "upbeat" picture, did not say whether Trump has recently tested negative, nor did he indicate when Trump's last negative test was.

Trump, his staff and his medical team have repeatedly refused to provide specifics about his testing regimen. Pressed by reporters last week, Conley said, "I don't want to go backwards."

Saturday's letter also did not address Trump's treatment protocol.

Centers for Disease Control and Prevention guidelines stipulate that those stricken with the virus should isolate themselves for at least 10 days after the onset of symptoms — with those suffering from more severe cases needing to isolate for up to 20 days. Trump first reported symptoms 10 days ago.

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The president's treatment included a strong steroid, dexamethasone, as well as an antibody cocktail produced by Regeneron. He required supplemental oxygen on two occasions after he started experiencing symptoms, according to his medical team.

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Trump tweeted after his interview that he "can't get it (immune), and can't give it." Twitter soon slapped the tweet with a warning and limited its ability to be retweeted or liked.

"This Tweet violated the Twitter Rules about spreading misleading and potentially harmful information related to COVID-19," Twitter wrote. "However, Twitter has determined that it may be in the public's interest for the Tweet to remain accessible."

Trump is set to return to the campaign trail Monday for a rally in Florida and to visit Pennsylvania and Iowa later in the week. On Saturday, he held his first public event at the White House since his diagnosis.

"It is disappearing," Trump said of the coronavirus as the number of cases across the country increases.

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Trump says Covid is 'disappearing' at first event since testing positive for coronavirus

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More than 215,000 people have died in the United States from the virus, according to NBC News counts.

Speaking Sunday on ABC News' "This Week," Trump's son Eric Trump said the president "got hit hard" within the first day of experiencing symptoms.

"And I can tell you, as a son, it's never fun watching your father fly off to Walter Reed on Marine One, right?" the younger Trump said, adding that his father "sounded 100 percent" by the time they spoke Saturday.

He then incorrectly said Trump had taken a "vaccine" to combat the virus (rather than therapeutics).

"It actually probably goes to speak to how good some of these vaccines that are being created are, and what my father's done on the vaccine front, no one could have done," he said, adding: "He worked to push this vaccine. And now my father just took it."

NBC News has confirmed that 23 people close to Trump and three Republican senators tested positive for Covid-19 in the days around the president's diagnosis.