Medical experts and political officials have said there are signs that social distancing is working in America and the spread of the coronavirus is slowing. But Dr. Anthony Fauci, the nation's top infectious disease expert, said the country can't loosen social restrictions yet and needs to be ready for a possible return of the virus.

"We are doing a very good job on mitigation, on the physical separation, the adherence to the guidelines," Fauci said on "CBS This Morning" Thursday.

A new model from the Institute for Health Metrics and Evaluation at the University of Washington shows COVID-19 deaths could total around 60,000 by August, a drop from earlier predictions that said there could be 100,000 to 200,000 deaths.

"That's good news," Fauci said about the model, but he said that doesn't mean we can pull back on mitigation. "We've got to continue in many respects to redouble our efforts at the mitigation of physical separation in order to keep those numbers down and hopefully even get them lower than what you've heard recently."

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With the bit of good news, many Americans are wondering if they will be able to return to something resembling normal life this summer. Fauci said it's possible, but steps need to be taken first to prevent a second wave of infections.

"When we pull back and try to open up the country, … we have to be prepared that when the infections start to rear their heads again that we have in place a very aggressive and effective way to identify, isolate, contact, trace, and make sure we don't have those spikes that we've seen now."

He also cautioned that different parts of the country will be able to "open up" at different times.

"New York City, the terrible ordeal that they've gone through, is very different from some of the places in the middle of the country or the mountain regions, so when you say get back to normal, it's not going to be a light switch that you turn on and off," he said. "It's going to be differential and gradual depending upon where you are and where the burden of infection is."

The "bottom line," he said, is that's it's "very likely" we will be progressing toward normalization as we get closer to April 30, the date the federal social distance guidelines were extended to.

"I think that's going to be a good time to look and see how quickly can we make that move to try and normalize," Fauci said. "Hopefully by the time we get to the summer, we will have taken many steps in that direction."

Fauci also commented on his remark on the Wall Street Journal podcast that people shouldn't "ever" shake hands again. He said the comment was "a little bit tongue-in-cheek," but "there was a bit of reality" to it.

"Respiratory infections, particularly brand-new, ominous respiratory infections like we're going through right now, are clearly spread, very much, not only by droplets, but by people touching their face, shaking hands, and that's the reason why we talk about washing hands so often," he said. "I don't think in reality that we're going to all of a sudden never again shake hands, but I think I threw that out there to get people to start thinking much more about personal hygiene and the way that impacts the spread of a really deadly infection."