President Trump asked Americans during Monday's coronavirus briefing to maintain their social distancing through the end of the month to bring the coronavirus under control.

And if people really do observe the stay-at-home orders, models suggest that the epidemic could wane by summer. There's also hope that the changing weather will help slow the spread of the virus, though that's far from certain.

But there's a problem. Even if things "get better all of a sudden," as the president suggested he hoped would happen, the virus will not have gone away.

"This virus is now in thousands, if not hundreds of thousands of locations around the world," said Mark Denison, director of the division of pediatric infectious diseases at the Vanderbilt University Medical Center. "And it's not finished with its human exploration."

Not that the virus is intentionally exploring, it's just doing what viruses do: infecting cells and making copies of itself. That doesn't happen when enough people are immune from infection, either because people have been exposed to the virus, and recovered, or because they've been vaccinated.

Virologists call people who don't have that immunity "naïve." Their immune system hasn't learned how to deal with the threat the virus represents.

"This virus has about 8 billion immune-naive people on the planet," said Denison. He worries that the virus could easily flare up again once people start going back to work and restarting their accustomed activities.

"This thing is scaring the hell out of me," said Denison.

"When the virus is gone, people are going to sit next to each other," Trump said, at sporting events and restaurants. But that may be farther off than the president thinks.

The best protection against the virus would be a vaccine. But that's probably at least a year away, even if the crash development programs now underway succeed.

Still, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said it may be possible to loosen societal restrictions sooner. "I don't think that you're going to have to say that the country cannot get back to a real degree of normalcy until you absolutely have a safe and effective vaccine," he said during the briefing.

A test that measures people's antibodies, and presumably their immunity, to the virus will be available widely by May, according to U.S. Public Health Service Adm. Brett Giroir.

That kind of test will be "so important," Fauci said, because then health officials will know how widely the virus has spread.

Broader testing capability, including antibody testing, would help the country reduce the kind of COVID-19 mitigation by social distancing that is in effect now. "We will have in place the capability of identifying [cases], contact tracing and isolating so it never gets out of hand," he said.

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