03 December 2025 -(Bloomberg Opinion) — An internal memo written by the Food and Drug Administration’s top vaccine regulator offers a concerning glimpse into the future of vaccine regulation in the US – and could have profound implications for both access to and the development of vaccines.
Vinay Prasad’s memo, which was leaked to the news media, makes alarming claims about the Covid-19 vaccine – including the assertion, made without any supporting evidence, that it has caused the death of “at least 10 children.” It also suggests that the FDA will make significant changes to the way vaccines are regulated.
The memo comes at a time of great turmoil at the agency, which intensified this week with the news of yet another leader’s potential exit, and amid increasingly aggressive efforts by Health Secretary Robert F. Kennedy Jr. to both undermine confidence in and limit access to vaccines.
Prasad made the extraordinary claim about the safety of Covid vaccines in the email to his staff at the FDA’s Center for Biologics Evaluation and Research (CBER). He said an internal investigation found the children died due to myocarditis, a form of heart inflammation. Yet he provided no data or research to support the claim – an irresponsible and dangerous approach to regulatory oversight.
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It is also wildly out of step with the agency’s typically careful process of reviewing safety data. Proving that a vaccine caused a death is a complex endeavor that requires significant evidence, explains Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, who previously served on the FDA’s vaccine advisory committee.
In this case, Offit says, regulators would need a raft of information, including an autopsy report that confirms a child had indeed died of myocarditis and not some other cause; documentation showing that the child wasn’t infected with Covid, which can also cause myocarditis; and evidence that they were not infected with one of the many other viruses that can cause fatal inflammation of the heart. If all the evidence pointed to the vaccine being the cause, the FDA’s next step would be to figure out exactly how the harm occurred.
Yet Prasad dropped the bombshell claims without providing proof that such a careful process had taken place. “He’s just raising this horrible specter that if you vaccinate your child, they may die,” Offit says. And he’s doing so, “knowing that the virus is still circulating, knowing that the virus is still causing hospitalizations and ICU admissions and deaths” in children.
Prasad also discussed a new framework for regulating vaccines, one that remains vague, but suggests companies could be asked to conduct much more onerous and expensive studies to prove the safety and efficacy of their vaccines. The goal, he said, is to “direct vaccine regulation towards evidence-based medicine.”
However, getting a new vaccine on the market already requires a rigorous, evidence-based process. When the FDA approved the first RSV vaccine in 2023, it marked the culmination of nearly 50 years of research to understand and develop a vaccine against the virus. To prove the vaccine worked, it was tested in multiple studies, including precisely the kind of large, gold-standard, placebo-controlled trial that Prasad routinely advocates for – in this case, one that enrolled 25,000 older adults.
And while new technologies like mRNA are speeding up vaccine development, the drugs must still undergo similarly massive studies to prove they are safe and effective. For example, last spring, Moderna published data suggesting its experimental mRNA flu vaccine is as good as or perhaps better than shots based on conventional technology. The two studies together enrolled more than 14,000 adults. Last month, Pfizer presented similarly promising data from its own mRNA-based flu shot trial, which recruited nearly 18,500 volunteers.
Prasad’s memo, meanwhile, also suggests changes are afoot for routine shots, including the seasonal flu vaccine. “We will revise the annual flu vaccine framework, which is an evidence-based catastrophe of low-quality evidence, poor surrogate assays, and uncertain vaccine effectiveness measured in case-control studies with poor methods,” he wrote.
Prasad didn’t explain what that revision would entail. But that single sentence could have profound implications. Public health officials have already struggled to convince Americans that the flu shot – an imperfect vaccine, but one that can prevent the worst outcomes of the virus – is worthwhile. Such inflammatory language about the shot (offered, again, without explanation or evidence) from the FDA’s top vaccine regulator is hardly likely to improve consumers’ confidence in its value.
Meanwhile, any regulatory changes that make it harder for people to access the vaccine could have dangerous consequences. Last year’s flu season was a reminder of the virus’ potential to cause severe illness: the CDC estimated it hospitalized 1.1 million Americans and killed 280 children.
The lack of specifics in the memo makes it difficult to assess the full impact on public health. Prasad has made accusations without identifying the data he believes is lacking, without outlining a better process, and without offering a timeline for when any of these changes might be implemented.
In the immediate term, though, the ambiguity is harmful to the environment for vaccine development. As Bloomberg News noted, shares of multiple Covid vaccine developers dipped on news of the memo and the anticipated scrutiny on their products.
It could also hold back investment in future vaccines. Drug developers depend on certainty from regulators about what is needed to approve new products. Instead, they are facing an agency in turmoil, increasingly driven by Prasad’s shifting notion of “gold-standard” science. All of this comes amid vocal skepticism and misinformation about vaccines coming from the highest reaches of US health agencies. Innovation will suffer for it – and so will public health.
This column reflects the personal views of the author and does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.
Lisa Jarvis is a Bloomberg Opinion columnist covering biotech, health care and the pharmaceutical industry. Previously, she was executive editor of Chemical & Engineering News.
(Disclaimer: The views and opinions expressed in this article are those of the authors and Parikh Worldwide Media does not officially endorse, and is not responsible or liable for them.)