Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield attends a Senate Appropriations subcommittee hearing on "Review of Coronavirus Response Efforts" on Capitol Hill in Washington, D.C., the United States, on Sept. 16, 2020. It will be the late second quarter or third quarter of 2021 before a COVID-19 vaccine is generally available to the American public, said Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield on Wednesday. (Andrew Harnik/Pool via Xinhua)

Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield attends a Senate Appropriations subcommittee hearing on "Review of Coronavirus Response Efforts" on Capitol Hill in Washington, D.C., the United States, on Sept. 16, 2020. It will be the late second quarter or third quarter of 2021 before a COVID-19 vaccine is generally available to the American public, said Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield on Wednesday. (Andrew Harnik/Pool via Xinhua)

Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield attends a Senate Appropriations subcommittee hearing on "Review of Coronavirus Response Efforts" on Capitol Hill in Washington, D.C., the United States, on Sept. 16, 2020. It will be the late second quarter or third quarter of 2021 before a COVID-19 vaccine is generally available to the American public, said Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield on Wednesday. (Andrew Harnik/Pool via Xinhua)

Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield attends a Senate Appropriations subcommittee hearing on "Review of Coronavirus Response Efforts" on Capitol Hill in Washington, D.C., the United States, on Sept. 16, 2020. It will be the late second quarter or third quarter of 2021 before a COVID-19 vaccine is generally available to the American public, said Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield on Wednesday. (Andrew Harnik/Pool via Xinhua)

Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield attends a Senate Appropriations subcommittee hearing on "Review of Coronavirus Response Efforts" on Capitol Hill in Washington, D.C., the United States, on Sept. 16, 2020. It will be the late second quarter or third quarter of 2021 before a COVID-19 vaccine is generally available to the American public, said Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield on Wednesday. (Andrew Harnik/Pool via Xinhua)

Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield attends a Senate Appropriations subcommittee hearing on "Review of Coronavirus Response Efforts" on Capitol Hill in Washington, D.C., the United States, on Sept. 16, 2020. It will be the late second quarter or third quarter of 2021 before a COVID-19 vaccine is generally available to the American public, said Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield on Wednesday. (Andrew Harnik/Pool via Xinhua)

Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield attends a Senate Appropriations subcommittee hearing on "Review of Coronavirus Response Efforts" on Capitol Hill in Washington, D.C., the United States, on Sept. 16, 2020. It will be the late second quarter or third quarter of 2021 before a COVID-19 vaccine is generally available to the American public, said Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield on Wednesday. (Andrew Harnik/Pool via Xinhua)

Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield attends a Senate Appropriations subcommittee hearing on "Review of Coronavirus Response Efforts" on Capitol Hill in Washington, D.C., the United States, on Sept. 16, 2020. It will be the late second quarter or third quarter of 2021 before a COVID-19 vaccine is generally available to the American public, said Director of the U.S. Centers for Disease Control and Prevention (CDC) Robert Redfield on Wednesday. (Andrew Harnik/Pool via Xinhua)