Dr. Anthony Fauci the director of the National Institute of Allergy and Infectious Diseases was asked why Europe has been able to largely contain the virus while the US has seen a rise in new cases.

Fauci said it was a complex question, but described some of the contributing factors. He first pointed out that many European countries locked down more wholly than the US.

"If you look at what happened in Europe, when they shut down or locked down or went to shelter in place — however you want to describe it — they really did it to the tune of about 95% plus of the country did that," Fauci said.

However, "when you actually look at what we did, even though we shut down, even though it created a great deal of difficulty, we really functionally shut down only about 50% in the sense of the totality of the country," Fauci added.

He also noted that some states had better success at following reopening guidelines than others.

"Some were followed very carefully and some were not," he said.

(With input from the agencies)