When President-elect Donald Trump said he would nominate one of the nation’s most prominent anti-vaccine movement leaders to lead the Health and Human Services Department, some social media users warned Americans to update their vaccines.

“IMPORTANT — vaccines could now be BANNED for part of this winter by Trump and RFK Jr, although hopefully any such ban would get halted with an injunction in court,” read one Nov. 15 Threads post. “GET CAUGHT UP ON VACCINES NOW — just in case.”

For two decades, Robert F. Kennedy Jr. has repeated false and misleading claims about science and public health. His unsuccessful presidential campaign of conspiracy theories earned him PolitiFact’s 2023 Lie of the Year. Kennedy, the nephew of Democratic President John F. Kennedy and the son of former presidential candidate Sen. Robert Kennedy Sr., D-N.Y., ran as an independent before suspending his campaign in August and backing Trump.

Scientists signaled their alarm at Trump’s decision to tap Kennedy. There are 13 agencies housed within that department, including the U.S. Centers for Disease Control and Prevention, the Food and Drug Administration and the National Institutes of Health.

Scientists were far from alone in expressing concern about what Kennedy could do as Health and Human Services secretary.

“Serious question — can he outlaw vaccines?” one Threads user asked Nov. 14. “Like if I want to get a Covid and flu vaccine next year, is it possible they won’t be available?”

The outlook is murky, partly because we can’t be sure what Kennedy will do. On. Nov. 6, before Trump officially tapped him for the seat, Kennedy told an NBC News reporter, “If vaccines are working for somebody, I’m not going to take them away.”

Vaccine law and policy experts told PolitiFact that Kennedy couldn’t unilaterally ban vaccines and that any effort to ban vaccines would likely face a legal battle. But Kennedy could still  reduce how accessible they are for Americans, they said. And some of his power rests on whether Trump’s administration can get buy-in from other lawmakers and public health leaders, some of whom Trump could also appoint.

Wendy Parmet, a Northeastern University law professor and the director of the law school’s Center for Health Policy and Law, said Kennedy couldn’t ban vaccines “by fiat,” or with one order or decree.

But he “could begin the process of having the FDA re-review the safety of vaccines and move to revoke or place restrictions on some vaccine approvals,” she said. “But this would take time and would undoubtedly be challenged in court.”

There are limits to the Health and Human Services secretary’s level of control over vaccines, Parmet said. But if he’s confirmed, Kennedy would “control the people who control the agencies that have a lot of authority over vaccines,” she said.

Kennedy could have those people act to limit vaccine access by revoking vaccines’ licenses or directing the CDC to change its vaccine messaging and recommendations, which would affect insurance coverage and medical practice, Parmet said.

Still, “there is no authority to ban vaccines as a group nationwide,” she said. “He would need an act of Congress for that.”

Dorit Reiss, a vaccine law and policy expert at University of California Law, San Francisco, told PolitiFact that federal regulations dictate how approved vaccines are taken off the market.

“You need to meet procedural requirements and show that the removal was not arbitrary and capricious,” she said. “And the main actor on that is the FDA commissioner, not the secretary, and we do not know who that will be” or whether they’ll be “sympathetic to the idea yet.”

The regulations say the FDA commissioner — whom Trump would also appoint — could begin the license revocation process if the commissioner finds that “the licensed product is not safe and effective for all of its intended uses.”

For years, Kennedy’s refrain has been that vaccines are unsafe. In July 2023, he told a podcaster that some vaccines “are probably averting more problems than they’re causing,” but in the same breath Kennedy maintained: “There’s no vaccine that is, you know, safe and effective.”

After notifying the manufacturer of the agency’s plan to revoke a vaccine license, the FDA commissioner would have to hold a hearing and also provide the manufacturer “reasonable” time to achieve compliance with whatever the government had asked of them.

“Manufacturers may well sue if they disagree,” Reiss said. “If there is no sufficient justification, (they) may win in court against the revocation.”

Kennedy could make vaccines less accessible, experts said

Reiss said it’s easier to stop the approval of new vaccines than it is to revoke access to existing vaccines, but it would require an FDA commissioner who is receptive to the idea.

She added that, as secretary, Kennedy could, for example, rescind emergency use authorizations for COVID-19 vaccinations for children, which would result in children younger than 12 losing access to those vaccines.

Kennedy could also nominate or remove members of federal advisory committees, including the Advisory Committee on Immunization Practices, which recommends vaccines that the CDC reviews and adopts. He could fill the committee with people who hold antivaccine beliefs who could then rescind vaccine recommendations, Reiss said.

Parmet said the CDC’s adopted vaccine recommendations determine the vaccines “covered without charge” under the Affordable Care Act and the immunizations available under the Vaccines for Children program, which provides vaccines to Medicaid-enrolled and uninsured children.

Kennedy could undermine grant programs that support state and local immunization programs, such as the CDC’s Section 317 Immunization Program, a reference to Section 317 of the Public Health Service Act. The program aims to ensure that children and adults are immunized by awarding federal grant money to state and local public health agencies to support vaccine purchases and operation costs, the 317 Coalition website said. Its 2023 report to Congress said that most of the program’s funding supports the mandatory Vaccines for Children program.

Pennsylvania’s Health Department says the program “plays a critical role in achieving national immunization coverage targets and reductions in disease.” Oklahoma’s State Department of Health described the program as “a precious national resource” that provides routine vaccination for people without insurance and responds to outbreaks of vaccine-preventable diseases.

Even without changes to official vaccine recommendations, Parmet said “informal changes” in CDC recommendations might change parents’ willingness to vaccinate their kids, influence states’ vaccination recommendation and impact some pediatricians’ practice.

“In other words, by simply changing the wording on its website,” the CDC could “discourage or reduce vaccine uptake,” she said.

Efforts to ban vaccines would face legal challenges, industry pushback

If Kennedy’s agency tried to enact a nationwide ban without any congressional action, the effort would likely face successful legal challenges, Parmet said.

It’s unclear whether a vaccine ban would win congressional support, but antivaccine lawmakers have made gains in statehouses nationwide in recent years, passing legislation that removes vaccine requirements for homeschooled children or preemptively prohibits schools from requiring students to receive COVID-19 vaccines.

Kennedy could also begin to have the FDA rereview vaccine safety and move to revoke or restrict some vaccine approvals. But those actions, “would take time and would undoubtedly be challenged in court,” Parmet said.

Reiss said existing laws and regulations could constrain Kennedy.

“He cannot violate express statutory provisions unless they change, and needs to contend with other agency heads,” such as the people in charge of the CDC and FDA, she said.

Just as he’ll name the Health and Human Services secretary and FDA commissioner, Trump will appoint the CDC and National Institutes of Health commissioners. In 2025, all these roles will need Senate approval, and the Senate will have a Republican majority in January. Trump had not announced his picks for these jobs as of Nov. 20.

Kennedy could “certainly try and persuade these people, and there’s some inter-dependence — they need the secretary to pass rules and to appoint people to advisory committees,” Reiss said. “But it’s the president who has the removal power over them, not the secretary.”

It’s also likely pharmaceutical companies would resist by lobbying against efforts to ban vaccines and suing the government, Reiss said.

PolitiFact researcher Caryn Baird contributed to this report.

This fact check was originally published by PolitiFact, which is part of the Poynter Institute. See the sources for this fact check here.