What is a febrile seizure or febrile convulsion?

When a child’s or infant’s body temperature rises because of an infection or inflammation, this can cause a febrile seizure, or febrile convulsion. It does not mean that the child has epilepsy.

Febrile seizures affect children under 6 years who have a temperature of 38° Celsius or more. It is most common between 6 months and 5 years, and especially from 6 months to 3 years. About 2 percent to 5 percent of children experience a febrile convulsion before they are 5 years old.

Seizures can look alarming to parents or caregivers, but most seizures are harmless and do not indicate a long-term medical problem. They are usually caused by a sudden spike in temperature.

If a child with a high temperature has a seizure and there is no clear cause or previous diagnosed neurological or developmental issue, it will be considered a febrile seizure.

Types of febrile seizure

[sick child with thermometer]
It is not uncommon for young children to experience a seizure when they have a fever.

There are two types of febrile seizure:

Simple febrile seizures last under 15 minutes and do not happen again during an infection

Complex febrile seizures may happen several times during an infection, and may last longer than 15 minutes

About 9 in every 10 febrile seizures are simple febrile seizures.

What causes febrile seizures?

Febrile seizures tend to occur because the child’s body temperature suddenly rises.

They mostly happen during the first day of the fever, but may occur as the high body temperature is coming down.

Infections that increase the risk of febrile seizures include gastroenteritis, tonsillitis, a urinary tract infection and other common infections.

Far less common but very serious are infections of the central nervous system that affect the brain and the spinal cord, including encephalitis and meningitis. Seizures linked to these conditions may have a more serious cause.

Do vaccinations cause seizures?

There is a very small risk of a febrile seizure after vaccination. Some studies suggest that 25 to 34 children out of every 100,000 have a febrile seizure after the measles, mumps, and rubella (MMR) vaccine.

The risk is even lower following the antidiphtheria, whooping cough, tetanus, polio, and hemophilus influenza type b vaccine (DTaP/IPV/Hib). The rate is around 6 to 9 cases out of every 100,000 vaccinations.

[child receiving vaccination]
After a routine vaccination, there is a very small chance of febrile seizure.

A febrile seizure that occurs soon after a vaccination is probably caused by the fever itself, rather than the vaccination.

The vaccination can cause the temperature to rise as the body “ramps up” to fight the intruder. This can lead to a febrile seizure.

After a DTP immunization, the risk is highest on the day of the vaccination when the fever is most likely to rise, but after the MMR vaccination, it may happen between 8 and 14 days later.

Research shows that while there is a small risk of a seizure following a vaccination, any long-term adverse effects are unlikely.

Doctors encourage immunization, and they urge parents to complete the vaccination schedule, even if a child has febrile seizures after a jab. This is because the risks and complications of diseases such as measles are far greater.

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How can parents recognize a febrile seizure?

A febrile seizure often happens at the beginning of an illness, as the fever starts, and often before the parents realize the child is sick.

The parents or caregivers may notice the following signs:

The child’s body becomes stiff

Arms and legs start to twitch, shake or jerk on both sides of the body

They may have trouble breathing

They will lose consciousness

They may lose control of their bladder or their bowels

They may vomit

They may foam at the mouth

Their eyes may roll back in the head

They may cry or moan.

Most seizures last only a few minutes, but they may cause drowsiness for up to an hour.

Complex febrile seizures may last over 15 minutes, and the child may experience several seizures while they are ill. The child may twitch on only one side of the body, known as a focal seizure.

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