WASHINGTON (NewsNation Now) — The director of the Centers for Disease Control and Prevention testified before Congress Wednesday, saying that any version of a coronavirus vaccine available this year would be in “very limited supply.”

CDC Director Dr. Robert Redfield reviewed the country’s COVID-19 response alongside two Health and Human Services Department officials Wednesday morning. HHS Assistant Secretary Admiral Brett Giroir and Assistant Secretary for Preparedness and Response Dr. Bob Kadlec joined Redfield before the Senate Subcommittee on Labor, Health and Human Services, Education and Related Agencies.

Despite President Donald Trump asserting Tuesday that a vaccine could be available within three to four weeks, Redfield estimated that a vaccine wouldn’t be broadly available to most of the U.S. population until the summer or fall of 2021.

Redfield discussed the plan before Senate lawmakers amid concerns that his agency had been pushed to revise several scientific assessments of the virus by Trump appointees. He rejected questions over whether the government’s timeline for states to be ready for a vaccine by Nov. 1 was politically motivated.

The CDC director told the Senate Appropriations Committee that the “scientific integrity” of his agency’s output “has not been compromised and it will not be compromised under my watch.”

Redfield also called face masks the most important and “powerful public health tool we have.”

“I might even go so far as to say that this facemask is more guaranteed to protect me against COVID than when I take a COVID vaccine,” Redfield said.

The hearing comes a day after the CDC released a report on coronavirus deaths in children and young adults in the U.S.

The CDC found that there were 121 deaths among people younger than age 21 from Feb. 21 through the end of July. According to a report, there’s a disproportionate percentage of deaths among Black and Hispanic youth.

The CDC found 54 were Hispanic, 35 were Black, and 17 were white, even though overall there are far more white Americans than Black and Hispanic.

Three out of four deaths occurred among Black, Hispanic and American Indian/Alaska Native persons, the agency announced on Twitter.

“It’s really pretty striking. It’s similar to what we see in adults,” and may reflect many things, including that many essential workers who have to go to work are Black and Hispanic parents, said Dr. Andrew Pavia, a pediatric infectious diseases expert at the University of Utah. He was not involved in the CDC study.