Washington, July 14 -- U.S. top infectious diseases expert Anthony Fauci said on Monday the United States is seeing a surge in new COVID-19 infections because the country never shut down entirely, according to a CNBC report.

"We did not shut down entirely," said Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, during a webinar with the Stanford School of Medicine.

"We need to draw back a few yards and say, 'OK, we can't stay shut down forever.' ...You've got to shut down but then you've got to gradually open," Fauci said.

He said he is "cautiously optimistic" scientists will be able to create at least one safe and effective vaccine by the end of the year or early 2021.

More than 3,353,000 COVID-19 cas...