SHERIDAN, WYOMING - December 2, 2025 - A leaked memo from FDA vaccine chief Vinay Prasad alleging that COVID-19 vaccines caused the deaths of 10 children has triggered a sharp backlash from scientific experts and investors, underscoring deep tensions inside U.S. vaccine regulation and adding fresh volatility for mRNA players Moderna and BioNTech.
An internal memo with external market consequences
In a six-page document titled "Deaths in children due to COVID-19 vaccines and CBER's path forward," Center for Biologics Evaluation and Research head Vinay Prasad claimed that an internal investigation had identified 10 child deaths "linked" to COVID-19 vaccination, based on reports in the Vaccine Adverse Events Reporting System (VAERS). The memo, published by The Washington Post, did not provide specific data, case details or manufacturer names.
Even in the absence of evidence, the impact was immediate. Moderna's stock, already down more than 40% year-to-date, fell a further 7% on Monday to $24.16, while BioNTech shares slipped 3.9% to $98.44. Analysts and vaccine makers now face the dual challenge of responding to heightened regulatory uncertainty and countering renewed public anxiety about safety across COVID-19, influenza and pneumonia vaccines.
Experts question VAERS-based conclusions and lack of transparency
Scientists and former regulators reacted with unusually strong criticism. "After years of working at the FDA I've never seen a memo like that," Peter Lurie, president of the Center for Science in the Public Interest and a former associate commissioner at the FDA, told BioSpace. "It's a screed that veers into things of no clear relevance whatsoever."
Lurie and others questioned why Prasad would rely on raw VAERS reports-which are unconfirmed and often incomplete-to draw conclusions about causality without presenting corroborating clinical data. In the memo, Prasad said VAERS cases had been investigated but did not specify whether standard FDA follow-up procedures were used.
Paul Offit, director of the Vaccine Education Center at the Children's Hospital of Philadelphia, highlighted the risks of making such claims without evidence. "He gives you no data to support that surprising assertion; he just puts it out there," Offit told BioSpace. "When you make a sensational claim like that, a frightening claim like that, at the very least, you owe it to the public to provide the evidence."
Data hierarchy under fire: observational studies vs. passive reporting
Beyond the headline allegation, experts are concerned by what they see as an inversion of the agency's usual evidence hierarchy. Prasad's memo criticized observational cohort and case-control data as having "notorious methdologic [sic] biases" without specifying the nature or impact of those biases. Lurie countered that "those data are usually from sources-clinical trials, people presenting to emergency rooms, etc.-considered preferable to VAERS reports," arguing that Prasad's position represents an "elevation of poor-quality data" and an attempt at "poking holes" in traditional clinical and cohort evidence.
Dorit Reiss, professor of law at UC Law San Francisco, raised alarm about the governance implications. "He's expressly not doing cost/benefit analysis, even though it's his job," she said. "This is a bad way to do policy" that demonstrates Prasad's lack of experience as a regulatory leader, Reiss added. "Essentially, he's announcing that he's making changes by fiat."
Prasad also signaled that dissent should remain behind closed doors and suggested resignation as an option for staff unwilling to comply with his framing-language observers see as at odds with the FDA's tradition of internal scientific debate and consensus-building.
Broader headwinds for vaccines under a politicized HHS
The memo lands in an already fragile environment for vaccines. Since Robert F. Kennedy Jr. became Secretary of Health and Human Services in February, anti-vaccine rhetoric has gained a louder platform inside the federal health apparatus. Kennedy has revamped the CDC's vaccine advisory committee, and the FDA has moved toward narrower vaccine approval guidelines.
Major manufacturers including Pfizer, Merck, GSK and Sanofi have reported declining sales as sentiment shifts and COVID-19 demand normalizes. Moderna, still searching for a post-pandemic growth narrative, looks particularly exposed. "We see further headwinds towards [Moderna's] declining COVID-19 franchise alongside further negative sentiment that this memo and subsequent actions may generate," William Blair analysts wrote on Monday.
The firm specifically flagged Moderna's updated trivalent flu vaccine, which showed a 26.6% efficacy improvement over a previous shot in a 40,000-patient Phase III head-to-head trial. While they described the dataset as "high-quality evidence," analysts cautioned that Prasad's memo could invite additional CBER scrutiny due to higher rates of non-serious adverse events such as fatigue, headache and myalgia-even in the absence of myocarditis cases.
Strategic outlook for vaccine developers and investors
For biopharma executives and investors, the episode underscores the importance of regulatory risk management in vaccine portfolios. Companies may need to prepare for:
- More probing CBER reviews of safety signals, even when supported by large, active-controlled trials.
- Increased volatility in vaccine-exposed stocks following internal leaks or public statements by senior regulators.
- A more politicized environment in which evidentiary standards and communication practices can shift quickly with leadership changes.
At the same time, sustained criticism from respected experts such as Lurie, Offit and Reiss may pressure FDA leadership and HHS to clarify the agency's stance on data standards, transparency and the role of VAERS versus clinical and observational evidence in vaccine safety decisions.
For ongoing updates on U.S. vaccine regulation, safety surveillance and manufacturer responses, industry stakeholders should closely monitor official communications from the FDA, CDC and leading vaccine companies.