The US Food and Drug Administration intends to put a “black box” warning on Covid-19 vaccines, according to two people familiar with the agency’s plans, the latest move by President Donald Trump’s health officials to undermine a vaccine that was a standout victory of his first term. The plan shocked outside experts, who said there was no basis for the warning.

A boxed warning, which appears at the top of prescribing information for medicines, is the agency’s most serious, designed to warn about risks such as death or life-threatening or disabling reactions that should be weighed against the intervention’s benefits. They can also be used when a risk might be lowered by using a medicine in a targeted way, such as only in certain groups.

Boxed warnings on opioids, for example, warn about risks of abuse, addiction, overdose and death. The acne medication Accutane carried a warning about the risks of birth defects when used during pregnancy. ACAM2000, a smallpox and mpox vaccine, has a warning about complications such as heart inflammation and encephalitis.

The plan to install the warnings for Covid-19 vaccines is being orchestrated by Dr. Vinay Prasad, the FDA’s chief medical and scientific officer and director of the agency’s Center for Biologics Evaluation and Research, according to one person, who declined to be named because they weren’t authorized to share the information publicly.

The plan has not been finalized and may still change. It wasn’t immediately clear whether the plans for the warnings, expected to be unveiled by the end of the year, would be applied only to mRNA vaccines or to all Covid-19 vaccines, or whether they would apply to all age groups. Three vaccines are approved by the FDA for use in the US, and two of them — from Pfizer and Moderna – use mRNA technology, which has been a key focus of the administration.

“Unless the FDA announces it, any claim about what it will do is pure speculation,” US Department of Health and Human Services spokesperson Andrew Nixon said Thursday.

In response to CNN’s inquiry about the FDA’s plans, Moderna pointed to a statement it issued in September about the safety of its Covid-19 vaccine, SpikeVax. It notes that the safety of its vaccine is “rigorously monitored by Moderna, the US FDA, and regulators in more than 90 countries,” and that, with more than a billion doses distributed worldwide, those systems “have not reported any new or undisclosed safety concerns in children or pregnant women.”

Pfizer too issued a statement in September supporting the safety and efficacy of its Covid-19 vaccine. The statements from both companies came after reports that federal health officials might seek to tie the vaccines to safety risks in pregnant women and children. Pfizer declined to provide further comment Thursday.

One study estimated that in their first year of use, Covid-19 vaccinations averted almost 20 million deaths around the world.

Children who received Covid-19 vaccines in the 2024-25 respiratory virus season also had a “substantially lower risk” of emergency department and urgent care visits related to the virus, according to a CDC report published Thursday. The vaccines were about 76% effective in preventing these outcomes among healthy children ages 9 months to 4 years and about 56% effective among children ages 5 to 17 compared with those who did not receive an updated vaccine for the 2024-25 season.

The record-speed development of Covid-19 vaccines during the pandemic, under the project dubbed Operation Warp Speed, was a crowning achievement of President Donald Trump’s first term, one that several Republican lawmakers have recently said should be awarded the Nobel Peace Prize. But Trump installed as his Health and Human Services Secretary Robert F. Kennedy Jr., a vaccine skeptic who has faced criticism from public health experts and lawmakers for his efforts to impose his personal views despite the science.

Administration targets vaccines

Kennedy and his allies have long questioned the safety and effectiveness of the Covid-19 vaccines, which were studied in placebo-controlled trials in about 75,000 people and given to millions of people in the US and around the world during the pandemic.

Prasad has been a controversial figure, both in his role at the FDA and previously, as a podcaster and professor in the Department of Epidemiology and Biostatistics at the University of California at San Francisco. A critic of the government’s response to the Covid-19 pandemic and vaccine policy, he was named CBER director under FDA Commissioner Dr. Marty Makary in May before resigning in July under pressure from the White House and right-wing activist Laura Loomer. Prasad then returned to the job weeks later.

In late November, Prasad sent a memo to staff within CBER, the division at the FDA that oversees vaccines, claiming that staff in the agency’s Office of Biostatistics and Pharmacovigilance had “found that at least 10 children have died after and because of receiving Covid-19 vaccination.” He did not provide additional information but promised “swift action” in response.

“The FDA takes very seriously any death that is attributed to a regulated medical product,” Nixon, of HHS, said Thursday.

Prasad focused on myocarditis, or heart inflammation, a very rare side effect after administration of the mRNA vaccines. It was detected with early use of those shots, when the first and second doses were recommended to be spaced as closely as three weeks apart, and was predominantly seen in boys and young men.

A presentation from the US Centers for Disease Control and Prevention in June said most adolescents and young adults recovered from myocarditis after vaccination, and it found no known deaths or heart transplants. Rates have declined significantly in more recent years as the recommended interval between the first and second doses in the initial series has been lengthened for the mRNA vaccines.

Still, the FDA said in May that it was requiring safety warnings in the prescribing information for Pfizer and Moderna’s Covid-19 vaccines about the risk of myocarditis and pericarditis, or inflammation of the tissue surrounding the heart, to be expanded to a broader age range. The labels now say, “the observed risk has been highest in males 12 years through 24 years of age.”

On Tuesday, Children’s Health Defense, the nonprofit led by Kennedy before his presidential bid, filed a citizen petition saying the agency should revoke the licenses for the vaccines. It argues that the mRNA vaccines are misbranded because they were initially approved under the standards of emergency use authorizations.

HHS also said this week that the FDA was looking into whether deaths “across multiple age groups” might be related to Covid-19 vaccines.

Prasad’s memo, which promised an overhaul of how the FDA regulates vaccines more broadly, drew alarm from outside public health experts, many of whom demanded to see the data supporting Prasad’s claims. A dozen former FDA commissioners wrote an open letter published in the New England Journal of Medicine expressing concern around “sweeping new FDA assertions about vaccine safety.”

‘Death by a thousand cuts’

“What’s happening now is death by a thousand cuts,” said a former federal health official who declined to be named because they were not authorized to share information with a reporter.

Recent messaging by the administration that goes against established scientific evidence – saying, for example, that vaccines are riskier when given together and that kids get too many vaccines that have potentially dangerous ingredients – is working to weaken the public’s confidence in lifesaving shots, the person said.

“What we’re watching is misinformation and lies in aggregate that will discourage the population from vaccination. It will lead us to, ultimately, to having loss of life unnecessarily, and it’s very disturbing,” the former official added.

Dr. Aaron Kesselheim, who runs the Program on Regulation, Therapeutics and Law at Harvard University, said these kinds of warnings can be initiated by the manufacturer or the FDA, but typically, the agency notifies the public that it’s looking into a safety question around a drug or vaccine. It may also convene an advisory committee — a panel of independent outside experts – to publicly vet the safety data and give advice.

None of these steps seems to have been taken so far.

“I guess my concern is that in this case, there’s not a process,” said Kesselheim, who has studied the impact of black box warnings on drug labels. “There isn’t that same opportunity for discussion and good-faith review of the data on which this decision is being made.

“My concern is that this will be seen as yet another in the long line of decisions that this FDA is making based on its own political goals, rather than after a dutiful and thoughtful and public review of the science.”

Nixon, the HHS spokesperson, said, “Any questions regarding potential safety issues are being thoroughly reviewed by the FDA’s established scientific and regulatory processes, ensuring that all decisions are based on rigorous, independent evaluation of the data.”

Others say they’re disturbed by the lack of transparency around whether deaths can be directly linked to the vaccine.

“The FDA has not released any data on how they determined that the Covid vaccines were linked to these pediatric deaths,” said Dr. Fiona Havers, a medical epidemiologist who resigned from the CDC in June over the administration’s interference in the agency’s vaccine programs.

“Very rare adverse events with vaccines can occur. I don’t know if they did in this case, because, again, they haven’t released any information,” she said. “But to only talk about potential harms for vaccines, without talking about the thousands of hospitalizations and the many pediatric deaths that these vaccines prevented, is irresponsible and not how our government should be messaging about vaccines to the public.”

Dr. Angela Rasmussen, a virologist at the University of Saskatchewan and co-editor-in-chief of the journal Vaccine, said the basis for a black-box warning was hard to understand.

“Scientifically, I don’t think it makes any sense at all, because we haven’t seen any of this data,” she said. “Presumably it’s going to say something like ‘this vaccine is dangerous.’ The FDA puts those on things when there are serious safety risks associated with them. And so it doesn’t make sense from an evidence-based perspective, at least based on any of the data that anybody’s seen.”

Still, the move doesn’t surprise her. Rasmussen said Prasad has a longstanding and well-documented antipathy toward the Covid-19 vaccine, as do other administration officials.

“Everything that they’ve done so far kind of signals to me that they’re very opposed to the Covid vaccines, and they’re really trying to manufacture evidence to justify something like that,” she said. “That’s been clear for a long time.”

Nixon said it’s “irresponsible for outside commentators to speculate about secondhand information they have not seen directly. We categorically reject the suggestion that anyone on our team is attempting to ‘manufacture evidence.’”