Interpreting FDA’s Request for Warning Labels on Influenza Vaccines About Febrile Seizures

In early January, the FDA sent out a letter to the manufacturers of 6 influenza vaccines, including: Fluzone (Sanofi), FluMist (AstraZeneca), Fluarix, FluLaval (both GSK), Afluria, and Flucelvax (both Seqirus), requesting they include an updated warning about the risk of febrile seizures.

“I think it's very smart to tell parents that, yes, your child's getting a vaccine, and they can have fever that goes up rapidly or down rapidly…Having children get febrile seizures is not so new for pediatrics, but more importantly, it is not associated with any kind of long-term seizure disorder or any kind of long-term central nervous system or brain disorder. It is a simple, short seizure associated with fever, and it is not having any long-term consequences,” said Sharon Nachman, MD, chief of pediatric infectious diseases, Stony Brook Children's Hospital.

In the letter, dated January 9, Vinay Prasad, MD, MPH, director, Center for Biologics Evaluation and Research, FDA, wrote to manufacturers providing some general data around these seizures during recent influenza vaccine seasons.

“The SCCS [self-controlled case series] analyses from the 2023-2024 and 2024-2025 seasons identified a significantly increased risks of febrile seizures in the first day following influenza vaccination. The incidence rate ratio (IRR) for febrile seizure following quadrivalent vaccine (2023-2024) in one data partner was 1.97 [95% CI: 1.09, 3.54] with an estimated attributable risk of 21.2 excess febrile seizure episodes per million standard dose quadrivalent vaccinations. In the same data partner, the IRR following trivalent vaccine (2024-2025) was 2.94 [95% CI: 1.72, 5.01] with an attributable risk of 44.2 excess febrile seizure episodes per million standard dose trivalent vaccinations.We consider this information to be “new safety information” as defined in section 505-1(b)(3) of the FDCA.”¹

Regarding the data shared in the FDA letter, Nachman says they reviewed several vaccines, but did not call out the data results of the individual vaccines.

“They looked at a bunch of different vaccines, and what they said is that there was a range of febrile seizures occurring with a risk anywhere from about 20 per a million doses given to children to about 30 per million doses given to children of increased risk for febrile seizures. So in their note, they actually suggested that they looked across several different vaccine types, and that's why they're suggesting that it's easier to do a blanket you're-at-risk, then start picking and choosing.”

Another problematic aspect of their data, according to Nachman, is that they focused only on 2 influenza seasons for the data they shared, and it does not demonstrate the variability associated with different respiratory virus seasons and vaccines.

“By looking at 2 years worth of seasons and those specific vaccines, they are kind of giving a very broad okay, you can have increased variable seizures. So from their perspective, I understand why they did it. From a pediatrician’s perspective, I do worry that we're giving parents the wrong information. They didn't look at other flu seasons. And as you know, every flu season means a different vaccine. So, it could have been something very specific to those 2 seasons,” Nachman said.

“In 2009 we had a huge shift, and it was the first time we saw [influenza A subtype] H1N1, and since then, we've had a couple of drifts with [influenza A subtype] H3N2, etc. It could be some drift in serotype leading to a vaccine, and then an increased fever response to those vaccines that cause the seizures and that may disappear next year when we have different serotypes of X of flu circulating and different vaccine components. While I appreciate the warning, I think it needs to be further explained to families as well as to providers.”

This is part 1 of 2-part interview. In the next episode, Nachman provides some clinical understanding of febrile seizures, and what clinicians and families should know in how to deal with them.

Reference
1. 2026 Safety and Availability Communications. FDA. Updated January 9, 2026. Accessed January 15, 2026. https://www.fda.gov/vaccines-blood-biologics/safety-availability-biologics/2026-safety-and-availability-communications