WASHINGTON - US COVID-19 cases driven by the Delta variant may double to 200,000 a day in the fall, said Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases, on Wednesday.

"Remember, just a couple of months ago, we were having about 10,000 cases a day," Fauci told McClatchy in an interview. "I think you're likely going to wind up somewhere between 100,000 and 200,000 cases."

The COVID-19 cases driven by the Delta variant are rising in a "very steep fashion" across the United States and the country could be "in trouble" entering the fall unless a large portion of unvaccinated Americans decide to get the shots, said Fauci.

"What we're seeing, because of this increase in transmissibility, and because we have about 93 million people in this country who are eligible to get vaccinated who don't get vaccinated - that you have a significant pool of vulnerable people," said Fauci.

The infectious disease expert said he is concerned the high number of unvaccinated people could lead to a stronger variant emerging that could combat the vaccines that have been given out.

"If we don't crush the outbreak to the point of getting the overwhelming proportion of the population vaccinated, then what will happen is the virus will continue to smolder through the fall into the winter, giving it ample chance to get a variant," Fauci said.

As of Aug 2, the 7-day rolling average of daily COVID-19 cases in the United States was 84,389, according to the US Centers for Disease Control and Prevention.