FDA Notifies Flu Vaccine Makers to Add Warning for Increased Febrile Seizure Risk in Young Children Day Following Vaccination

The FDA notified influenza vaccine makers that a warning about an increased febrile seizure risk in babies and preschoolers the day following flu vaccination should be added. This announcement was made in safety labeling notification letters sent on January 9, 2026, to the manufacturers of 6 different flu vaccines: Fluzone (Sanofi), Flumist (MedImmune, LLC), Fluarix, Flulaval (both GSK), Afluria, and Flucelvax (both Seqirus).^1,2

According to a news release from MedPage Today, the new language in the label would state, “In 2 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 manufacturers have 30 days to respond to the FDA’s request.¹

To support their recommendation, the FDA referenced a September 2025 study published in Vaccine. After observing nearly 10 million influenza vaccinees across the collected databases, the authors’ combined meta-analysis demonstrated no statistically significant elevation in risk for any outcome except febrile seizure and transient ischemic attack (TIA). A small, statistically significant elevation in risk was observed for febrile seizure (0–1-day risk interval) following standard-dose (incidence rate ratio [IRR]: 1.68; [95% CI 1.17–2.43]) or any (IRR: 1.67 [95% CI 1.16–2.41]) influenza vaccine. Additionally, the investigators found a statistically significant elevation in risk for TIA (1–21-day risk interval) following a standard-dose (IRR: 1.28 [95% CI 1.04–1.59]) or any (IRR: 1.29 [95% CI 1.05–1.59]) influenza vaccine.³

Febrile seizures are convulsions in a child caused by a fever (≥ 102ºF), often related to an infection. According to Mayo Clinic, febrile seizures can occur in young, healthy children who have normal development and have not demonstrated any prior neurological symptoms. Children having a febrile seizure may shake all over and lose consciousness, or sometimes may be very stiff and twitch in one area of the body. Usually, febrile seizures are harmless, last a few minutes, and do not indicate any serious health problems, but complex seizures can last longer than 15 minutes, occur more than once within a 24-hour period, or be confined to 1 side of the child’s body. Mayo Clinic recommends that additional help be sought if the seizure lasts longer than 5 minutes or is accompanied by vomiting, a stiff neck, extreme sleepiness, and breathing problems.⁴

In 2025, the influenza vaccine—among others—has been under scrutiny and faced a plethora of changes in policy. The US Department of Health and Human Services announced the cancellation of a series of grants for late-stage development of prepandemic influenza vaccines (including one against H5N1 avian influenza), and the Advisory Committee on Immunization Practices voted to recommend that all US adults receive seasonal influenza vaccines in single-dose, thimerosal-free formulations.^5-7 Pharmacists are significant in educating caregivers on the importance of annual influenza vaccination, regardless of prior infection or vaccination history, to protect their children against circulating strains and to remain adherent to formulation changes.⁸

REFERENCES

1. Rudd T. FDA Calls for New Warning on Flu Shots. MedPage Today. January 14, 2026. Accessed January 15, 2026. https://www.medpagetoday.com/pediatrics/vaccines/119429

2. US Food & Drug Administration. 2026 Safety and Availability Communications. Updated January 9, 2026. Accessed January 15, 2026. https://www.fda.gov/vaccines-blood-biologics/safety-availability-biologics/2026-safety-and-availability-communications

3. Lloyd PC, Acharya G, Zhao H, et al. Safety monitoring of health outcomes following influenza vaccination during the 2023–2024 season among U.S. Commercially-insured individuals aged 6 months through 64 years: Self-controlled case series analyses. Vaccine. 2025;63:127614. doi:10.1016/j.vaccine.2025.127614

4. Mayo Clinic. Overview– Febrile Seizure. Accessed January 15, 2026. https://www.mayoclinic.org/diseases-conditions/febrile-seizure/symptoms-causes/syc-20372522

5. Halpern L. HHS Cancels Millions in Pandemic Influenza mRNA Vaccine Development Grants. Pharmacy Times. May 30, 2025. Accessed January 15, 2026. https://www.pharmacytimes.com/view/hhs-cancels-millions-in-pandemic-influenza-mrna-vaccine-development-grants

6. Halpern L. ACIP Recommends Adults Receive Seasonal, Single-Dose Influenza Vaccines Free of Thimerosal. Pharmacy Times. June 26, 2025. Accessed January 15, 2026. https://www.pharmacytimes.com/view/acip-recommends-adults-receive-seasonal-single-dose-influenza-vaccines-free-of-thimerosal

7. Halpern L. Thimerosal Reenters Public Debate as ACIP Scrutinizes Use in Influenza Vaccines. Pharmacy Times. June 27, 2025. Accessed January 15, 2026. https://www.pharmacytimes.com/view/thimerosal-reenters-public-debate-as-acip-scrutinizes-use-in-influenza-vaccines

8. Valletti D. Optimal Timing of Influenza Vaccination in Young Children: Practical Implications for Pharmacists. Pharmacy Times. September 19, 2025. Accessed January 15, 2026. https://www.pharmacytimes.com/view/optimal-timing-of-influenza-vaccination-in-young-children-practical-implications-for-pharmacists