Once a coronavirus vaccine is approved as safe and effective, Americans should have widespread access within a reasonable time, Dr. Anthony Fauci assured lawmakers Friday.

Appearing before a House panel investigating the nation’s response to the pandemic, Fauci expressed “cautious” optimism that a vaccine would be available, particularly by next year.

“I believe, ultimately, over a period of time in 2021, that Americans will be able to get it,” Fauci said, referring to the vaccine.

There will be a priority list for who gets early vaccinations. “I don’t think we will have everybody getting it immediately,” Fauci explained.

But “ultimately, within a reasonable time, the plans allow for any American who needs the vaccine to get it,” he added.

Under direction from the White House, federal health authorities are carrying out a plan dubbed Operation Warp Speed to manufacture 300 million doses of a vaccine on a compressed timeline.

Fauci, the nation’s top infectious disease official, said a quarter-million people have expressed interest in taking part in studies of experimental vaccines for the coronavirus.

He said that 250,000 people have registered on a government website to take part in vaccine trials, which are pivotal for establishing safety and effectiveness. Not all patients who volunteer to take part in clinical trials are eligible to participate.

Fauci was joined by Centers for Disease Control and Prevention head Dr. Robert Redfield and Health and Human Services testing czar Adm. Brett Giroir.

Giroir acknowledged that currently it’s not possible for the US to return all coronavirus test results to patients in two to three days. He blamed overwhelming demand across the nation.

Many health experts say that COVID-19 results are almost worthless when delivered after two or three days because by then the window for contact tracing has closed.

The latest government data shows about 75 percent of testing results are coming back within five days, but the remainder are taking longer, Giroir told lawmakers.

Rapid, widespread testing is critical to containing the coronavirus outbreak, but the US effort has been plagued by supply shortages and backlogs since the earliest days of the outbreak.