Dr. Anthony Fauci, the nation's top infectious disease expert, said Tuesday that the unique qualities of the “unprecedented” novel coronavirus that helped it “explode” into a global pandemic represent the kind of nightmarish scenario that keeps him up at night.

“What keeps me up at night is the emergence of a brand new infection, likely jumping species from an animal, that's respiratory born, highly transmissible, with a high degree of morbidity and mortality. And, lo and behold, that's where we are right now,” Fauci said during a livestreamed interview Tuesday with The Economic Club of Washington, D.C. "And the reason it's so unprecedented, it exploded upon us."

“Everyone is at risk,” the director of the National Institute of Allergy and Infectious Diseases said. “With this, everyone seems vulnerable, with a disease that's highly transmissible.”

“This is really unprecedented,” he added.

Fauci said the illness “exploded in a way that's been unprecedented in a compact period of time.”

Later in the interview, Fauci reiterated his view that the pandemic will persist through the fall.

“I’m almost certain it will come back. The virus is so transmissible,” he said. “In my mind, it’s inevitable that we will have a return of the virus or that maybe it never went away.”

He added that it will come down to “how we handle it” in the fall that “will determine our fate.”

“If by that time we have put into place all of the countermeasures … if we address that, we will do reasonably well,” he said. “If we don’t do that, we could be in for a bad fall and a bad winter.”

At the same time, Fauci repeated his view that a widely available vaccine won’t be available for at least “likely a year to a year and a half.”

“Hopefully by that time we get to this coming winter, we will know whether we have a safe and effective vaccine,” he said. “The challenge would then be to scale it up.”