FDA asks six flu vaccine makers to warn of small febrile seizure risk in young children

The U.S. Food and Drug Administration’s Center for Biologics Evaluation and Research asked makers of six widely used influenza vaccines to update product labeling to warn of a small increased risk of febrile seizures in children aged 6 months through 4 years during the first day after vaccination.

The agency sent safety‑label change notifications to manufacturers on Jan. 9, 2026 and gave companies 30 days to accept the suggested language, propose modifications, or submit a rebuttal. The letters named Sanofi’s Fluzone, AstraZeneca’s FluMist, GSK’s FluLaval and Fluarix, and CSL Seqirus’s Afluria and Flucelvax. FDA documents note those vaccines have been marketed in the United States for many years; AFLURIA was approved in 2007 and Fluzone has been available since 1980.

FDA based the request on two post‑marketing observational analyses conducted through the agency’s Biologics Effectiveness and Safety System, or BEST, covering the 2023–2024 and 2024–2025 influenza seasons. Analysts used three commercial insurance claims datasets and employed a self‑controlled case series design that compared event rates in a 0–1 day risk window after vaccination with a control period 8–63 days later. The agency stated an increased risk of febrile seizures was observed on the first day after vaccination with standard‑dose trivalent (2024–2025 formula) and quadrivalent (2023–2024 formula) influenza vaccines in children 6 months through 4 years.

The FDA suggested placing this language in the Warnings and Precautions section of product labels and cross‑referencing it in the pediatric adverse reactions section: “In two separate postmarketing observational studies, an increased risk of febrile seizures was observed during the first day following vaccination with standard dose trivalent (2024‑2025) and quadrivalent (2023‑2024) influenza vaccines in children 6 months through 4 years of age.” The agency’s materials also include an attributable risk estimate of 44.2 excess febrile seizure episodes per million standard‑dose trivalent vaccinations.

Clinicians and public health officials stressed that febrile seizures are typically brief convulsions linked to fever and rarely cause lasting neurological damage. Background estimates place febrile seizures in roughly 2 to 5 percent of children in the affected age range and note infections such as influenza and common respiratory viruses commonly precipitate such events. At the same time, the Centers for Disease Control and Prevention continues to recommend annual influenza vaccination for people aged six months and older to prevent serious illness, hospitalizations and death.

The regulatory action reflects FDA’s characterization of the finding as “new safety information” under section 505‑1(b)(3) of the Federal Food, Drug, and Cosmetic Act and proceeds under the agency’s authority to require labeling updates. The analyses are tied to a Vaccine journal publication cited in the agency correspondence. Manufacturers now have a defined window to respond; if labels are updated, clinicians will need to incorporate the new language into conversations with caregivers.

Public health experts say 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 is narrow and quantitative and, if implemented carefully, can help parents and clinicians weigh a small immediate risk against the known benefits of influenza vaccination. The agency’s labeling requests arrive as FDA also reviews safety language for other products, underscoring an active period of regulatory reassessment.