By Adam Cancryn, CNN

(CNN) — In the weeks before they moved to oust Dr. Susan Monarez as head of the US Centers for Disease Control and Prevention, top US Department of Health and Human Services officials repeatedly pressed her in meetings to commit to signing off on potential new vaccine restrictions, two people familiar with the matter said.

Among those present: Jim O’Neill, the No. 2 HHS official, who has since become the CDC’s new acting chief, the people said.

It was not immediately clear what role O’Neill played in the meetings or whether he directly sought to convince Monarez to pledge her support for recommendations that might limit access to proven vaccines, two people familiar with the matter told CNN.

HHS Secretary Robert F. Kennedy Jr., and his deputy chief of staff, Stefanie Spear, led the internal push to secure Monarez’s allegiance, the people said.

But O’Neill’s participation in the meetings, which has not been previously reported, has spurred questions among staffers about whether he would stand up to political pressure in running the CDC, which is charged with making critical public health recommendations that determine Americans’ access to a wide range of vaccines. It could also complicate efforts to ease tensions between HHS leadership and CDC staff, who are still reeling from mass layoffs and a shooting this month that killed a police officer and left employees traumatized.

An HHS spokesperson declined to comment, instead referring to a note Kennedy sent to CDC staff on Thursday announcing O’Neill’s appointment as acting director.

“Together, we will rebuild this institution into what it was always meant to be: a guardian of America’s health and security,” Kennedy wrote in the email, adding that O’Neill would “help advance this mission.”

On Friday, O’Neill acknowledged his new role atop the CDC in a post on X that criticized the agency for losing trust during President Joe Biden’s administration and asserted “we are helping the agency earn back the trust it had squandered.”

In the meetings with Kennedy, O’Neill and other HHS officials, Monarez refused to bend to the pressure, insisting on several occasions that she would not back any actions before examining the underlying evidence, the people said.

The standoff culminated on Wednesday with the Trump administration declaring she’d been fired — a high-profile moment that spurred the resignations of four other senior officials and tipped the agency into crisis.

O’Neill has had little discernible interaction with the CDC’s rank and file since joining the administration in June, the people familiar with the matter said.

But Kennedy, a longtime CDC critic and leading antivaccine activist prior to joining the Trump administration, has taken the agency to task in the aftermath of Monarez’s ouster.

“There’s a lot of trouble at CDC, and it’s going to require getting rid of some people over the long term in order for us to change the institutional culture,” he said during a news conference in Texas on Thursday.

Kennedy has sought to advance major changes to the federal government’s evaluation of vaccines in recent months, despite growing misgivings among career scientists at the CDC and elsewhere within the department.

The dispute with Monarez grew primarily out of the work done by the Advisory Committee on Immunization Practices, a panel of independent experts who make recommendations to the CDC on vaccine policy.

Kennedy fired all of the committee’s members in June and appointed a new slate that includes allies who have questioned the safety of vaccines, sparking concern inside and outside the CDC that they would seek new restrictions on long-accepted vaccines.

The advisory committee is scheduled to meet in mid-September to examine a range of vaccines, including recommendations for the hepatitis B vaccine — an immunization long targeted by Kennedy and others who have sowed doubt about its inclusion among the vaccines routinely given to children.

O’Neill, a longtime biotech investor close to billionaire Peter Thiel who did a stint at HHS during the George W. Bush administration, has said little publicly about vaccines and kept a low public profile since becoming Kennedy’s second-in-command.

During his confirmation hearing in May, O’Neill told Sen. Bill Cassidy, a Louisiana Republican, that he’s “very strongly pro-vaccine” and supported the CDC’s vaccination schedule.

Some Kennedy allies have suggested that his appointment might help dampen the blowback over Monarez’s ouster, especially among Republican lawmakers alarmed by the recent chaos. That is because some view O’Neill as a more experienced government hand with more mainstream health care credentials who can provide some stability, two people familiar with the discussions said.

Still, critics said there’s little expectation that O’Neill will serve as a bulwark against any future efforts to limit vaccine access — and, given his dual role at HHS and CDC, instead now appears positioned to only accelerate Kennedy’s agenda.

“I don’t know who actually will be making those calls, but I do understand that when we’ve been working on these data that we make decisions from, a lot of that is coming from the White House, is coming from HHS,” Dr. Dan Jernigan, one of the senior CDC officials who resigned after Monarez’s firing, said Thursday on “The Source with Kaitlan Collins.” “And so I don’t know exactly where we’re going to go next.”

This story has been updated with additional developments.

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