Thomas Frieden:

Any time we come back out again, we are at risk of seeing a resurgence of COVID disease.

Even New York City, where we have had a terrible epidemic, with more than 15,000 people killed, that's as many as were killed in a whole year of the great influenza pandemic of 1918. This is the worst health threat in a century.

And yet, even so, most New Yorkers aren't immune, haven't been infected, and it could get much worse. That means we need to loosen the faucet on physical distancing gradually. We need to do it in stages, because, when you loosen once, it may be three or four weeks before you see the spread of the disease from that loosening, if it happens.

If you do it in a faster pace, you could have a roaring infection that rages through society, that kills people in your nursing homes, that endangers health care workers, and that's very hard to reverse.

So, it's not just, unfortunately, a question of a second wave. It's the question of multiple waves that we're at risk for if we don't emerge from our sheltering in place very carefully, gradually, protecting those who are most vulnerable, using hand sanitizer, using other ways to physically distance, so we reduce the risk.