WASHINGTON (NewsNation Now) — The nation’s top infectious diseases expert, Dr. Anthony Fauci, and Centers of Disease Control and Prevention Director Dr. Robert Redfield addressed concerns about a coronavirus vaccine and inconsistencies on virus prevention guidance at a Senate hearing Wednesday.

Fauci told the Senate Committee on Health, Education, Labor and Pensions that government scientists should know about whether they have a safe and effective COVID-19 vaccine by the end of this year.

In an attempt to quell concerns, Fauci said he “certainly would” take a vaccine authorized by the Food and Drug Administration.

Several vaccines are in the final stage of testing in the U.S. On Wednesday, Johnson & Johnson announced it’s beginning the final phase of a trial for a single-shot coronavirus vaccine, and should have results by year-end or early next year. Pfizer Inc. and Moderna Inc. are also in late stage trials.

Dr. Brett Giroir, an assistant secretary at the Department of Health and Human Services who also testified before the Senate committee, echoed Fauci’s confidence in the safety of a vaccine approved by the FDA. He said he’d “have no hesitancy” to take the vaccine, adding that people should have discussions with their health care providers about it as well.

Redfield said he expects there to be about 700 million doses of vaccines available by late March or April, enough for 350 million people.

Redfield also addressed criticism about recent contradictions in guidance provided by the CDC.

He said the agency’s change to guidance for testing for asymptomatic individuals with close contact to a COVID-19 positive person was poorly written. It has since been updated to make it clear that such individuals should get a test, he said.

The CDC will release new guidance on the role of aerosolized coronavirus in its spread, Redfield said. The agency took down a Sept. 18 update to its transmission guidance that mentioned airborne virus for the first time, as it lacked the needed technical review.

FDA Commissioner Dr. Stephen Hahn was also present at the Senate hearing Wednesday.

The hearing comes as the country reaches a grim milestone of 200,000 coronavirus-related deaths, the highest in the world, according to Johns Hopkins University’s count.