The attempted ousting of the director of the Centers for Disease Control and Prevention (CDC) and resignations of four high-profile officials on Wednesday were the latest developments in turmoil that has been plaguing the federal health agency.

Over the past few months, the CDC has seen several resignations, mass layoffs, shakeups of key committees and major changes in vaccine policy.

At the center is Health and Human Services (HHS) Secretary Robert F. Kennedy Jr., who has claimed he wants to restore trust in the CDC and weed out alleged corruption.

Here is a timeline of changes that have occurred at CDC.

Nov. 22, 2024

Then-President-elect Donald Trump nominates Dr. Dave Weldon to lead the CDC.

Jan. 23, 2025

Trump selects Susan Monarez to be acting CDC director.

Feb. 18, 2025

Dr. Nirav Shah, principal deputy director of the CDC, resigns, saying he made the decision to leave independently, according to local reports. Shah led the CDC’s bird flu response.

March 13, 2025

The White House pulls the nomination of Weldon for CDC director ahead of his appearance before the Senate Health, Education, Labor and Pensions (HELP) Committee because he didn’t have the votes to be confirmed.

Weldon was expected to be grilled on his past comments questioning vaccine safety, such as falsely suggesting vaccines are linked to autism.

March 24, 2025

Monarez is nominated by Trump to be CDC director. The president writes on Truth Social that she brings “decades of experience championing Innovation, Transparency, and strong Public Health Systems.”

March 25, 2025

Five high-level CDC officials depart from the agency, in a move described as “retirements,” according to the Associated Press.

The departures included:

• Leslie Ann Dauphin, founding director of the National Center for State, Tribal, Local, and Territorial Public Health Infrastructure and Workforce.
• Karen Remley, director of the National Center on Birth Defects and Developmental Disabilities.
• Sam Posner, head of the Office of Science.
• Debra Lubar, chief operating officer.
• Leandris Liburd, acting director for the Office of Health Equity.

April 1, 2025

Mass layoffs begin at HHS, affecting more than 10,000 people. This includes about 2,400 CDC employees, which is about one-fifth of the workforce.

April 3, 2025

Kennedy announces that some programs and employees would be reinstated because they were mistakenly cut. This includes the division at the CDC that handles lead surveillance.

It’s later revealed the HHS hired back more than 450 CDC employees who had been fired.

May 27, 2025

Kennedy announced the CDC will no longer be recommending the COVID-19 vaccine for “healthy children and pregnant women.”

The CDC later updates the guidance to a “shared clinical decision making” model — leaving the decision to vaccinate between patients or parents and a doctor.

June 5, 2025

Dr. Lakshmi Panagiotakopoulos, who oversaw the CDC’s recommendations for COVID-19 vaccines, resigns after mixed messages over who would be eligible for vaccines.

June 9, 2025

Kennedy removes all 17 members of CDC’s vaccine advisory panel, the Advisory Committee for Immunization Practices (ACIP), which makes recommendations on the safety, efficacy and clinical need of vaccines.

Kennedy says replacing the sitting committee members would help restore public trust and claims they were plagued by conflicts of interest.

June 11, 2025

Kennedy appoints eight hand-selected members to sit on the ACIP, including some who have expressed vaccine-skeptic views.

June 16, 2025

Dr. Fiona Havers, who led the CDC’s tracking of hospitalizations from COVID-19 and RSV, resigns, citing concerns over how the data could be used to shape national vaccine policy, according to Reuters.

June 25, 2025

In ACIP’s first meeting since Kennedy replaced all the members, the committee says it will be reviewing the current childhood immunization schedule.

June 26, 2025

ACIP recommends an RSV monoclonal antibody shot for babies but recommends against flu vaccines containing the preservative thimerosal.

Thimerosal is a mercury-based preservative, which is used to prevent microbial contamination of vaccines. Most flu vaccines currently used in the U.S. contain little to no thimerosal, but both the Food and Drug Administration and the CDC say there is no evidence low doses of thimerosal in vaccines cause harm other than minor reactions at the injection site, such as redness or swelling. 

July 29, 2025

The Senate confirms Monarez as CDC director by a vote of 51-47 along party lines.

She is the first CDC director nominee who required Senate confirmation after Congress passed a law requiring it in 2022. 

Aug. 8, 2025

A gunman opens fire at CDC headquarters in Atlanta, resulting in the death of a police officer. Investigators and sources close to the gunman later said he was harboring a years-long grievance against the COVID-19 vaccine.

Aug. 12, 2025

Monarez sends a note to the company’s more than 10,000 employees, linking misinformation to the deadly shooting at CDC.

Aug. 27, 2025

HHS sends out a post on X stating that Monarez is “no longer director” of the CDC.

Sources tell ABC News that Kennedy and Stefanie Spear, his principal deputy chief of staff, called on Monarez to support changes to COVID vaccine policy and the firings of high-level staff, a source familiar with the conversations told ABC News, which Monarez would not commit to.

Lawyers for Monarez state she will not leave her post and that, because she was appointed by Congress, Trump has to personally dismiss her.

The White House, which has the authority to dismiss Monarez, followed up late Wednesday night with a statement saying Monarez was indeed “terminated.”

Following HHS’s statement about Monarez’s departure, four other senior career officials at the CDC also resign:

• Dr. Deb Houry, Chief Medical Officer and Deputy Director for Program and Science.
• Dr. Dan Jernigan, Director of the National Center for Emerging and Zoonotic Infectious Diseases.
• Dr. Demetre Daskalakis, Director of the National Center for Immunization and Respiratory Diseases.
• Dr. Jennifer Layden, Director for the Office of Public Health Data, Surveillance, and Technology.

In a departure email to colleagues, Daskalakis writes that he will no longer serve in his role “because of the ongoing weaponizing of public health.”

Aug. 28, 2025

Monarez’s attorneys say she has still not heard directly from the president on the matter and has not had any further communications with the White House since the previous evening.

The White House named Health and Human Services Deputy Secretary Jim O’Neill as the interim director Thursday evening.

ABC News’ Will McDuffie, Sony Salzman and Dr. Jade Cobern contributed to this report.