WASHINGTON (AP) — Dr. Anthony Fauci said Friday that he remains confident that a coronavirus vaccine will be ready by early next year, telling lawmakers that a quarter-million Americans already have volunteered to take part in clinical trials.

But if the future looks encouraging, public health alarms are still going off in the present. Officials testifying with Fauci at a contentious House hearing acknowledged that the U.S. remains unable to deliver all COVID-19 test results within two or three days, and they jointly pleaded with Americans to comply with basic precautions such as wearing masks, avoiding crowds, and washing their hands frequently.

Those simple steps can deliver “the same bang for the buck as if we just shut the entire economy down,” said a frustrated Dr. Robert Redfield, director of the Centers for Disease Control and Prevention, adding that he has studies to back that up.

Looking ahead, Fauci said he’s “cautiously optimistic that we will have a vaccine by the end of this year and as we go into 2021. I don’t think it’s dreaming … I believe it’s a reality (and) will be shown to be reality.” As the government’s top infectious disease expert, Fauci heads the National Institute of Allergy and Infectious Diseases.

Under White House orders, federal health agencies and the Defense Department are carrying out a plan dubbed Operation Warp Speed to deliver 300 million vaccine doses on a compressed timeline. That will happen only after the Food and Drug Administration determines that one or more vaccines are safe and effective. Several candidates are being tested.

Don’t look for a mass nationwide vaccination right away, Fauci told lawmakers. There will be a priority list based on recommendations from scientific advisers. Topping the list could be critical workers, such as as medical personnel, or vulnerable groups of people such as older adults with other underlying health problems.

“But ultimately, within a reasonable period of time, the plans now allow for any American who needs a vaccine to get it within the year 2021,” Fauci said.

Fauci, Redfield, and Department of Health and Human Services “testing czar” Admiral Brett Giroir testified at a moment when early progress against the coronavirus seems to have been frittered away. High numbers of new cases cloud the nation’s path. The three officials appeared before a special House panel investigating the government’s pandemic response, itself sharply divided along party lines.