The agency, or the CDC, has been at the forefront of pushing COVID-19 vaccination during the pandemic since the first vaccine received emergency authorization late last year.

"What percent of CDC employees are vaccinated?" Sen. Bill Cassidy (R-La.) asked Dr. Rochelle Walensky, the CDC's head, during a Senate Health Committee hearing in Washington.

"We're actively encouraging vaccination in all of our employees and doing outreach in order to get our agency vaccinated," Walensky responded.

Sen. Richard Burr (R-N.C.), the top Republican on the panel, revisited the topic just before the hearing ended.

"Do you really not know the answer to the number of vaccinated individuals at CDC or did you just not want to answer Sen. Cassidy's question?" Burr wondered.

Walensky declined to answer directly.

"We're still actively working on collecting those data and those data are updated in real-time," she said.

Burr asked for the numbers to be sent to the committee by Nov. 8.

"We are working toward updating that data. I would have to speak with my staff about where we are and whether those numbers are going to be available on Monday," Walensky said.