FDA Requests Febrile Seizure Warning for Six Major Flu Vaccines Following Post-Marketing Safety Analysis
Key Insights
The FDA has requested six major influenza (search) vaccine manufacturers to add warnings about increased febrile seizure risk in children aged 6 months to 4 years during the first day after vaccination.
Post-marketing observational studies covering nearly 10 million vaccinees found a statistically significant 68% increased risk of febrile seizures (search) with an attributable risk of 44.2 excess episodes per million vaccinations.
The affected vaccines include widely used products from Sanofi, GSK, AstraZeneca, and CSL Seqirus (search), with manufacturers given 30 days to respond to the labeling change request.
The U.S. Food and Drug Administration has requested six major influenza (search) vaccine manufacturers to update their product labeling to include warnings about a small but statistically significant increased risk of febrile seizures (search) in young children. The safety labeling notification letters, sent on January 9, 2026, target vaccines from Sanofi (Fluzone), AstraZeneca (FluMist), GSK (Fluarix and FluLaval (search)), and CSL Seqirus (search) (Afluria and Flucelvax).
Post-Marketing Safety Analysis Reveals Increased Risk
The FDA's request stems from two separate post-marketing observational studies conducted through the agency's Biologics Effectiveness and Safety System (BEST), covering the 2023-2024 and 2024-2025 influenza (search) seasons. The analysis examined nearly 10 million influenza vaccinees across three commercial insurance claims datasets using a self-controlled case series design.
The studies found an increased risk of febrile seizures (search) during the first day following vaccination with standard-dose trivalent (2024-2025 formula) and quadrivalent (2023-2024 formula) influenza (search) vaccines in children aged 6 months through 4 years. Specifically, researchers observed a statistically significant elevation in febrile seizure risk following standard-dose vaccination, with an incidence rate ratio of 1.68 (95% CI 1.17-2.43) for the 0-1 day risk interval.
The FDA has calculated an attributable risk estimate of 44.2 excess febrile seizure episodes per million standard-dose trivalent vaccinations, providing a quantitative measure of the additional risk.
Proposed Warning Language and Regulatory Timeline
The FDA has suggested specific language for inclusion in the Warnings and Precautions section of product labels: "In two separate postmarketing observational studies, an increased risk of febrile seizures (search) was observed during the first day following vaccination with standard dose trivalent (2024-2025) and quadrivalent (2023-2024) influenza (search) vaccines in children 6 months through 4 years of age."
Manufacturers have been given 30 days to respond to the FDA's request, with options to accept the suggested language, propose modifications, or submit a rebuttal. The regulatory action proceeds under the agency's authority to require labeling updates when new safety information emerges under section 505-1(b)(3) of the Federal Food, Drug, and Cosmetic Act.
Clinical Context and Risk Assessment
Febrile seizures (search) are convulsions in children caused by fever (≥102°F), often related to infections. According to Mayo Clinic guidance referenced in the analysis, febrile seizures can occur in young, healthy children with normal development who have not demonstrated prior neurological symptoms. These episodes typically involve shaking, loss of consciousness, or stiffness and twitching in specific body areas.
Background estimates indicate that febrile seizures (search) affect roughly 2 to 5 percent of children in the affected age range, with infections such as influenza (search) and common respiratory viruses commonly precipitating such events. Most febrile seizures are harmless, lasting only a few minutes and not indicating serious health problems.
Continued Vaccination Recommendations
Despite the identified risk, the Centers for Disease Control and Prevention continues to recommend annual influenza (search) vaccination for people aged six months and older to prevent serious illness, hospitalizations, and death. Public health experts emphasize that transparent communication is essential to maintain confidence in routine childhood immunization, particularly in communities with limited access to medical care and higher baseline risks from influenza.
The warning represents a narrow and quantitative risk assessment that, if implemented carefully, can help parents and clinicians weigh a small immediate risk against the known benefits of influenza (search) vaccination. The affected vaccines have been marketed in the United States for many years, with some products like Fluzone available since 1980 and Afluria approved in 2007.
Broader Regulatory Context
The labeling requests arrive during an active period of regulatory reassessment for influenza (search) vaccines. In 2025, the Advisory Committee on Immunization Practices voted to recommend that all U.S. adults receive seasonal influenza vaccines in single-dose, thimerosal-free formulations, while the U.S. Department of Health and Human Services announced the cancellation of grants for late-stage development of prepandemic influenza vaccines.