Washington, Aug 1 (IANS): US top infectious disease expert Dr. Anthony Fauci said incomplete shutdown is among factors contributing to the surging COVID-19 cases in the country.

The director of the National Institute of Allergy and Infectious Diseases made the remarks at a House subcommittee hearing when asked why Europe has been able to largely contain the virus while the United States has seen a rise in new cases, Xinhua news agency reported on Friday.

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

"When you actually look at what we did ... we really functionally shut down only about 50 percent in the sense of the totality of the country," he said.

The senior expert also told lawmakers that he is "cautiously optimistic" that the coronavirus vaccine being developed by Moderna and his agency will be successful.

The US COVID-19 cases reached 4.49 million with over 152,000 fatalities as of 10.35 Eastern Time on Friday, according to a tally by Johns Hopkins University (JHU).