The FDA Adds Febrile Seizure Warning to Flu Vaccines and Moderna COVID Shot
FDA labeling changes and emerging safety data intensify scrutiny over pediatric seizure risks and informed consent
Recent regulatory action by the U.S. Food and Drug Administration (FDA) is drawing renewed attention to a safety signal that has long concerned many parents: febrile seizures following vaccination in young children.
A febrile seizure is a convulsion triggered by fever. These seizures typically occur in infants and young children when body temperature rises rapidly. Episodes can involve shaking, stiffening, loss of awareness, or uncontrolled movements. While often described as brief, febrile seizures are deeply frightening for families and represent a neurological event, not merely a benign reaction.
Febrile seizures most commonly occur between six months and five years of age.
In January 2026, the FDA formally instructed several influenza vaccine manufacturers to update their product information to include warnings about febrile seizure risk. The decision followed post-marketing safety analyses identifying a statistically significant increase in seizures triggered by fever within one day of injection among children aged six months through four years.
The agency classified the findings as “new safety information” and stated that the data “suggest a causal relationship.”
Vaccines Affected by the FDA Labeling Directive
According to FDA notification letters, the labeling update applies to standard-dose trivalent and quadrivalent influenza vaccines manufactured by major pharmaceutical companies, including:
• Sanofi Pasteur influenza vaccines
• AstraZeneca, including FluMist
• GlaxoSmithKline (GSK) influenza vaccines
• CSL Seqirus influenza vaccines
The FDA specified that updated warnings must reference an increased risk of febrile seizures within one day of vaccination in children aged 6 months through 4 years.
Manufacturers were given 30 days to accept the revised warning language or submit alternative proposals.
FDA Identifies Measurable Excess Risk
The FDA’s review of observational data from the 2023–2024 and 2024–2025 influenza seasons produced quantifiable estimates:
• 21.2 excess febrile seizure episodes per million quadrivalent doses
• 44.2 excess febrile seizure episodes per million trivalent doses
While regulators described the overall risk as low, the requirement for mandatory label changes signals that the agency considers the safety signal clinically and legally significant.
Similar Seizure Signal Reported for Moderna’s COVID Shot
The influenza labeling directive arrives alongside a peer-reviewed FDA-funded study published in Vaccine, examining febrile seizure risk following Moderna’s COVID-19 shot in young children.
Researchers reported a statistically significant increase in febrile seizures within one day of injection, particularly among children aged 2 to 4 years. The study estimated seizure risk during the first day post-injection was approximately 2.5 times higher than during later comparison periods.
Despite the findings, the publication included a disclaimer stating the conclusions “should not be construed to represent FDA’s views or policies.”
It remains unclear whether regulators issued a formal public advisory when the seizure signal first appeared as a preprint in 2024.
A Risk Historically Minimized
Febrile seizures — convulsions triggered by fever — occur most commonly in children between six months and five years of age. Public health messaging has often characterized these events as brief and generally harmless.
Brian Hooker, Ph.D., CHD’s Chief Scientific Officer, disputes that framing:
“Any seizure is bad, period.”
Hooker points to evidence suggesting:
• Even seizures labeled “simple” may increase epilepsy risk
• “Complex” seizures may carry greater long-term neurological consequences
A 2023 review in Frontiers in Cell and Developmental Biology warned that seizures during early brain development may contribute to later neurological disease.
A 2024 review in Pediatric Neurology concluded febrile seizures may be associated with:
• Cognitive deficits
• Structural brain abnormalities
• Elevated epilepsy risk in a subset of children
Study Design Leaves Long-Term Questions
Critics note that many postmarketing safety studies observe outcomes only for weeks or months following injection.
Karl Jablonowski, Ph.D., senior research scientist at Children’s Health Defense, cautioned:
“Neurological harm would likely only be evident throughout the child’s development.”
The FDA BEST System study tracked insurance claims for only 63 days post-injection and did not evaluate long-term neurodevelopmental outcomes.
Consistency in Risk Disclosure Under Scrutiny
The FDA’s decision to mandate febrile seizure warnings for influenza vaccines has prompted broader questions about regulatory consistency and risk communication.
Observers have questioned:
• Why warnings sometimes appear years after rollout
• Whether similar seizure signals across vaccine categories are treated equally
• Whether parents received timely, transparent disclosure
When safety communications follow widespread use rather than precede it, families are left questioning whether informed consent was ever fully informed.
The Bottom Line
The addition of febrile seizure warnings to influenza vaccine labels represents a notable regulatory shift — one acknowledging a measurable post-injection risk in young children.
At the same time, similar seizure findings associated with pediatric COVID-19 shots highlight a concern many families continue to raise:
Timely, transparent safety communication remains inconsistent.
For parents and caregivers, the issue is not whether a risk is described as “rare,” but whether it was clearly disclosed before consent was given.
Sources:
Michael Nevradakis, Ph.D., The Defender
FDA Asks for Warning on Flu Vaccines About Febrile Seizure Risks in Kids
Suzanne Burdick, Ph.D., The Defender
Moderna COVID Vaccine Linked to Higher Risk of Febrile Seizure.
Frontiers in Cell and Developmental Biology
The long-term neurodevelopmental outcomes of febrile seizures and underlying mechanisms
Pediatric Neurology
Febrile Seizures, Ongoing Epileptiform Activity, and the Resulting Long-term Consequences: Lessons from Animal Models
Mayo Clinic – Febrile seizures
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