Dr. Rochelle Walensky, the director of the Centers for Disease Control and Prevention, will step down from her position on June 30, she announced on Friday.

In an agencywide meeting, Dr. Walensky admitted to mixed emotions about her decision and broke down in tears, according to people on a conference call with her.

“I took on this role with the goal of leaving behind the dark days of the pandemic and moving the C.D.C. — and public health — into a much better and more trusted place,” she said in an email to agency staff that followed the call.

It was unclear who would lead the agency after her departure.

During her tenure, Dr. Walensky noted in the email, the agency administered more than 670 million vaccine doses and provided clinical guidance om vaccination, schools and businesses and “protected the country and the world from the greatest infectious disease threat we have seen in over 100 years.”

Dr. Walensky took the helm of the beleaguered agency in January 2021. She had a near-impossible task ahead of her: restoring the reputation of the once storied C.D.C. when public trust in the agency was at a low.

Her email to staff seemed to suggest she believed she had improved the agency’s reputation at least to some extent.

“We collectively moved C.D.C. forward, reorganizing the agency and embarking on the necessary work to orient the enterprise toward public health action and foster accountability, timeliness, and transparency in our work,” she said.

This is a developing story. Please check back for updates.