The US Food and Drug Administration (FDA) is reportedly planning its most serious warning for Covid-19 vaccines, a “black box” label, according to two sources familiar with the agency’s plans. This decision has alarmed outside experts who say there is no scientific basis for such a warning.
A black box warning appears at the top of a medicine’s prescribing information. It is the FDA’s strongest type of warning, designed to alert patients and doctors to life-threatening or disabling risks. Such warnings are usually used when there is a known danger that needs careful consideration against a medicine’s benefits.
For example, opioids carry black box warnings about addiction, abuse, overdose, and death. Accutane, a drug for acne, warns about birth defects during pregnancy. The ACAM2000 vaccine for smallpox and mpox carries warnings about rare but serious complications like heart inflammation and encephalitis.
The plan to add this warning for Covid-19 vaccines is said to be led by Dr. Vinay Prasad, the FDA’s chief medical and scientific officer and director of the agency’s Center for Biologics Evaluation and Research (CBER), according to a source who spoke anonymously.
It is important to note that the plan has not been finalized. Officials have not clarified whether the warning would target mRNA vaccines specifically, all Covid-19 vaccines, or all age groups. The FDA has approved three Covid-19 vaccines in the US, with Pfizer and Moderna using mRNA technology.
“Unless the FDA announces it, any claim about what it will do is pure speculation,” said Andrew Nixon, a spokesperson for the US Department of Health and Human Services (HHS).
In response to inquiries, Moderna pointed to its September statement affirming that its vaccine, SpikeVax, is “rigorously monitored by Moderna, the US FDA, and regulators in more than 90 countries.” Moderna emphasized that over a billion doses have been distributed without new or undisclosed safety concerns in children or pregnant women.
Pfizer also issued a statement supporting the safety and effectiveness of its Covid-19 vaccine in September. Both statements came after reports that federal officials were considering tying the vaccines to potential risks in children and pregnant women.
Studies show that Covid-19 vaccines have saved millions of lives. One estimate suggested that nearly 20 million deaths were prevented worldwide during the first year of vaccine rollout.
A recent CDC report also showed that children vaccinated during the 2024-25 respiratory virus season had a “substantially lower risk” of emergency department visits due to Covid-19. Vaccines were about 76% effective for children aged 9 months to 4 years and 56% effective for children aged 5 to 17.
The rapid development of Covid-19 vaccines, under Operation Warp Speed, was one of President Donald Trump’s major accomplishments. Some Republican lawmakers even suggested the effort deserved a Nobel Peace Prize.
However, Trump later appointed Robert F. Kennedy Jr., a vaccine skeptic, as his Health and Human Services Secretary. Kennedy has been criticized for allowing personal views to influence vaccine policy, despite scientific evidence supporting their safety.
Prasad has been a controversial figure at the FDA and beyond. He previously served as a professor and podcaster, often criticizing government Covid-19 policies. He was named CBER director in May, resigned in July under pressure, and then returned weeks later.
In November, Prasad sent a memo claiming that at least 10 children had died after receiving Covid-19 vaccines. He promised “swift action” but provided no further details.
“The FDA takes very seriously any death that is attributed to a regulated medical product,” said Nixon.
Prasad has highlighted myocarditis, a rare heart inflammation following mRNA vaccines, mostly in young males. Early doses spaced closely together showed higher rates, but recent data shows most adolescents recover fully, and the risk has declined with longer intervals between doses.
The FDA already requires safety warnings for Pfizer and Moderna vaccines about myocarditis and pericarditis. Current labels note that the highest observed risk is in males aged 12 to 24.
Children’s Health Defense, led by Kennedy, filed a petition urging the FDA to revoke mRNA vaccine licenses. They claim the vaccines are “misbranded” because they were initially approved under emergency use authorizations.
HHS said the FDA is investigating deaths across multiple age groups to see if they are linked to Covid-19 vaccines.
Outside experts are concerned about the lack of transparency and data. A dozen former FDA commissioners wrote an open letter warning against “sweeping new FDA assertions about vaccine safety.”
A former federal health official described the situation as “death by a thousand cuts,” warning that misinformation could erode public trust in lifesaving vaccines and lead to unnecessary deaths.
Dr. Aaron Kesselheim of Harvard noted that black box warnings usually follow a clear process, including public advisory panels. None of these steps appear to have occurred in this case, raising concerns about political influence on FDA decisions.
Dr. Fiona Havers, a former CDC epidemiologist, said, “To only talk about potential harms for vaccines, without talking about the thousands of hospitalizations and pediatric deaths these vaccines prevented, is irresponsible.”
Virologist Dr. Angela Rasmussen questioned the scientific basis for a black box warning, noting, “We haven’t seen any data suggesting serious risks. This seems politically motivated rather than science-driven.”
HHS rejected claims of evidence manipulation. Nixon said, “Any questions regarding potential safety issues are being thoroughly reviewed by the FDA’s established scientific and regulatory processes, ensuring all decisions are based on rigorous, independent evaluation of the data.”
The situation remains fluid. Experts and the public await clarity from the FDA before making any decisions about Covid-19 vaccine safety and communication. Meanwhile, millions of lives continue to benefit from vaccines that have been tested and monitored for safety worldwide.
