U.S. top infectious disease expert Anthony Fauci said on Friday that he is "cautiously optimistic" that the U.S. could have coronavirus vaccine in late fall or early winter this year.

Fauci said, "We hope that by the time we get into late fall and early winter, we will have in fact a vaccine that we can say that would be safe and effective. One can never guarantee the safety or effectiveness unless you do the trial, but we are cautiously optimistic this will be successful."

He made the remarks while testifying at the coronavirus crisis hearing in Capitol Hill.

During the hearing, Fauci was been asked about why the Europe did better job than the U.S. in the aspect of containing COVID-19.

Fauci answered that the European countries fully locked down to curb the spread of the virus. However, the shutdown of the U.S. only worked for about 50 percent of the country.

As of Friday morning, the U.S. reported more than 4.49 million COVID-19 cases, with 152,082 deaths, according to the latest tally from Johns Hopkins University.

(Cover: Dr. Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, arrives to testify before the House Select Subcommittee on the Coronavirus Crisis hearing in Washington, D.C., U.S., July 31, 2020. /Reuters)