U.S. Centers for Disease Control and Prevention Director Dr. Rochelle Walensky late Thursday endorsed the Pfizer coronavirus vaccine booster shot for younger at-risk workers, which is seen as a rare break from the agency's Advisory Committee on Immunization Practices panel.

The panel had recommended the booster for Americans 65 and older and for those over 50 with underlying medical conditions, but voted against the younger at-risk worker recommendation.

Walensky put it back in, saying it aligns with a U.S. Food and Drug Administration booster authorization from earlier this week.

Rochelle Walensky, director of the U.S. Centers for Disease Control and Prevention (CDC), speaks during a Senate Health, Education, Labor, and Pensions Committee confirmation hearing in Washington, D.C

Rochelle Walensky, director of the U.S. Centers for Disease Control and Prevention (CDC), speaks during a Senate Health, Education, Labor, and Pensions Committee confirmation hearing in Washington, D.C., U.S., on Tuesday, July 20, 2021. (Photographer: J. Scott Applewhite/AP Photo/Bloomberg via Getty Images (Photographer: J. Scott Applewhite/AP Photo/Bloomberg via Getty Images)

"As CDC Director, it is my job to recognize where our actions can have the greatest impact," Walensky said in a statement. "At CDC, we are tasked with analyzing complex, often imperfect data to make concrete recommendations that optimize health. In a pandemic, even with uncertainty, we must take actions that we anticipate will do the greatest good."

The younger at-risk group includes teachers and front-line medical workers.

CDC directors rarely reverse panel decisions and in doing so can risk undermining the process, The New York Times reported. The lateness of the CDC statement showed the complex nature of deciding who needs the booster most. 

But Walensky aligned herself with the FDA and the White House, which recommended giving boosters to more Americans. 

"I am surprised that Dr. Walensky overturned one of the four ACIP votes today, and I believe others will be as well," Dr. Yvonne Maldonado, an infectious disease expert on the committee, told The Times. But she agreed the vote was close and didn't begrudge Walensky's decision. 

An email was sent out to the panelists minutes before the CDC statement was released, advising them Walenksy was reversing the decision.

"I am hoping to share this news with you before you see it in the press," Dr. Amanda Cohn, who oversaw the panel, wrote, according to The Times.

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The panel had offered the option of a booster for those ages 18 to 49 who have chronic health problems and want one. But the advisers refused to go further and open boosters to otherwise healthy front-line health care workers who aren't at risk of severe illness but want to avoid even a mild infection.

Walensky opened Thursday's meeting by stressing that vaccinating the unvaccinated remains the top goal "here in America and around the world." Around 55% of Americans are fully vaccinated. 

The CDC and the panel did not immediately respond to after-hour emails from Fox News.

The Associated Press contributed to this report.