[2][3] Prior to her appointment at the CDC, she had served as the chief of the Division of Infectious Diseases at Massachusetts General Hospital and a professor of medicine at Harvard Medical School.

[11] Walensky was a professor of medicine at Harvard Medical School from 2012 to 2020, and served as chief of the division of infectious diseases at Massachusetts General Hospital from 2017 to 2020.

She conducted research that used the methods of decision science, Monte Carlo mathematical simulation and cost-effectiveness analyses to promote access to HIV care in the US and internationally.

Walensky worked to improve HIV screening and care in South Africa, led health policy initiatives, and researched clinical trial design and evaluation in a variety of settings.

[20] Early in the pandemic and prior to vaccine availability, she used model-based analyses to demonstrate how SARS screening strategies could be used to safely reopen college campuses.

[28] On August 26, as was widely expected,[29] the U.S. Supreme Court struck down the extension as unconstitutional, ruling that only the U.S. Congress had the authority to issue such a moratorium.

[30] As the pandemic entered the Omicron variant wave, Walensky acknowledged that officials on the CDC response team were burned out,[31] and tried to reassign workers.

Walensky and other top officials had a plan to dissolve large parts of the pandemic response team, which has more than 1,500 staffers, and reassign members to their original posts.

Walensky shelved the plan with the emergence of Omicron as cases began to tick up across the U.S.,[31] bringing morale lower than ever at the CDC.

"What we’re seeing is policy failures, accompanied by poor messaging," said Anne N. Sosin, a public health researcher at Dartmouth College, who added that the rest of the administration is also to blame.

"[33] During a January 26, 2022 news conference about the rise of the Omicron variant and high hospitalization rates, Dr. Walensky said the nation should not ease up on COVID-19 safety protocols, saying, "Milder does not mean mild and we cannot look past the strain on our health systems and substantial number of deaths."

[35] On August 17, 2022, she delivered a sweeping rebuke of her agency's handling of the coronavirus pandemic, saying it had failed to respond quickly enough and needed to be overhauled.

[37] On November 29, 2022, Dr. Walensky marked the 50th year of the Tuskegee Syphilis Study,[38] and said that she would be meeting with colleagues and leaders in public health the following day, with a commitment to "ethical research & practice".