‘Maybe I’m Immune, I Don’t Know’

President Trump returned to the White House yesterday night, a little hobbled by the coronavirus but with his typical bravado intact. After arriving in Marine One, the president walked up a flight of stairs, turned toward the live television cameras and removed his mask. Then he saluted and walked inside, where several masked people appeared to be standing.

He tweeted a video of himself soon afterward in which he declared that he was already “better” and that “maybe I’m immune, I don’t know.” But just hours earlier, a White House physician had acknowledged to reporters that the president was not yet out of danger.

Speaking from outside Walter Reed National Military Medical Center, Sean Conley, the president’s physician, said Trump’s medical team was waiting to see if his condition remained stable through the weekend before taking “that final deep sigh of relief.”

Conley said Trump had received steady doses of the antiviral drug remdesivir and the steroid dexamethasone, which is considered beneficial to coronavirus patients who are severely ill. He affirmed that the president had improved steadily over the previous 24 hours. But he dodged certain questions, including about Trump’s lung function and the date of his last negative coronavirus test.

In the video Trump posted on Twitter, he echoed statements he had made in another tweet earlier in the day urging Americans to be calm and not to worry too much about the virus.

“Don’t let it dominate you — don’t be afraid of it,” he said. “You’re going to beat it. We have the best medical equipment, we have the best medicines.” The virus has killed more than 210,000 people in the United States.

Trump also said that he expected a virus vaccine to be made available “momentarily,” an analysis that runs against the statements of medical experts.

The White House is still holding out hope that a coronavirus vaccine could be approved before Election Day — and it doesn’t want too many safety checks to stand in the way.

Top administration officials have refused to authorize strict new guidelines for the emergency release of a vaccine, objecting to a stipulation that would effectively make it impossible for a vaccine to be authorized before the election on Nov. 3, people familiar with the process told The Times.

Officials at the Food and Drug Administration are trying to do an end-around to guarantee that any approved vaccine meets the guidelines. They may share the standards with an outside advisory committee that would meet publicly before a vaccine was authorized, in hopes that the committee will enforce the guidelines, regardless of the White House’s reaction.

The Centers for Disease Control and Prevention released new guidelines on Monday affirming something that scientists now widely accept: The coronavirus is transmitted through the air.

But the new language stopped short of what the C.D.C. had put forward last month, in a set of guidelines that were abruptly yanked from its website. That original language had said the virus could be spread by “aerosols, produced when an infected person coughs, sneezes, sings, talks, or breathes.”

The new guidelines are less explicit about the means of transmission, and emphasize that while the virus is spread through the air, it’s more common to get it when in close contact with someone who is infected — defining close contact as being within six feet of the person for at least 15 minutes.

The previous guidelines had referred to the coronavirus as “an airborne virus,” a term that — while widely accepted as truthful by the medical community — may have forced hospitals to treat infected patients in special rooms and caused health care workers to wear N95 masks anywhere in a hospital.