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 having 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 after 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, provided clinical guidance on vaccination and advice to schools and businesses, and “protected the country and the world from the greatest infectious disease threat we have seen in over 100 years.”