Causes

Usually, a higher than normal body temperature causes febrile seizures. Even a low-grade fever can trigger a febrile seizure.

Infection

The fevers that trigger febrile seizures are usually caused by a viral infection, and less commonly by a bacterial infection. The flu (influenza) virus and the virus that causes roseola, which often are accompanied by high fevers, appear to be most frequently associated with febrile seizures.

Post-vaccination seizures

The risk of febrile seizures may increase after some childhood vaccinations. These include the diphtheria, tetanus and pertussis vaccine and the measles-mumps-rubella vaccine. A child can develop a low-grade fever after a vaccination. The fever, not the vaccine, causes the seizure.