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Peds Geek M.D.

Fevers and Seizures

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This week I was interviewed by Tony Leys, health reporter at the Des Moines Register, about vaccine exemptions in Iowa schools. It was a good article, and I think the issue was portrayed fairly. Near the end of the article I was paraphrased as such:

"Boonstra advised her that combination shots can slightly raise the risk of fever, which can occasionally cause seizures. But he said even the seizures tend not to be dangerous."

You might be thinking, "Dr. Boonstra thinks vaccines are safe, but certain ones can cause seizures?" I could understand that. So let's go over what I meant. I might have phrased it as:

The adjective febrile (or fever-associated) is important here, because there are a lot of kinds of seizures, but febrile seizures are the most common, and among the least concerning.

What are febrile seizures?

A seizure is a sudden surge of electrical activity in the brain. A febrile seizure, simply put, is when a fever makes the electrical activity go off. No one knows exactly why a fever can cause a seizure, and it's not really well understood whether the likelihood of a febrile seizure is increased by how high the fever gets, or how quickly it rises. Around 4% of kids will have a febrile seizure at some point in their lives. They are often due to a fever from a viral infection like influenza, but any fever for any reason can cause a febrile seizure.

A child that has a febrile seizure will lose consciousness and likely shake his or her whole body. They are usually brief, less than two minutes, though in the moment it may feel like an eternity to a parent. After a seizure, a child will usually be "post-ictal," meaning they will be very disoriented for fifteen minutes or longer (sometimes hours). During this time, the child will be awake, but may not know where they are or recognize family members. This is one way to help tell a true seizure apart from other events like breath holding spells.

Are febrile seizures dangerous?

In general, no. Seizures can be very scary, and leave a parent feeling helpless. But simple febrile seizures (ones lasting less than 15 minutes) do not cause brain damage and are not associated with long term neurological effects, like epilepsy (a seizure disorder). Around 1% of the population has epilepsy, and this isn't changed if a child has had a single, simple febrile seizure. However, children who have multiple febrile seizures may be at an increased risk of epilepsy (around a 2.4% chance). Epilepsy in this situation is probably not caused by the febrile seizures. Instead, it's likely that people that develop epilepsy were at an increased risk of febrile seizures as children.

What should I do if my child has a febrile seizure?

As difficult as it may be, don't panic. Most febrile seizures are brief, and not dangerous. Your child's brain is not being harmed. There are a few steps you can take to make sure no accidents happen during the seizure. From the AAP's parents' site healthychildren.org:

  1. Place her on the floor or bed away from any hard or sharp objects.
  2. Turn her head to the side so that any saliva or vomit can drain from her mouth.
  3. Do not put anything into her mouth; she will not swallow her tongue.
  4. Call your child's doctor.
  5. If the seizure does not stop after 5 minutes, call 911 or your local emergency number.

What about vaccines and febrile seizures?

Since anything that causes a fever can theoretically, in rare cases, cause a febrile seizure, then a vaccine can do so. Fever happens after vaccination because fever is a part of activating the immune system to respond to a an illness or a vaccine. This is perhaps best studied after the measles-mumps-rubella (MMR) vaccine, which causes about one to two extra febrile seizures per one thousand vaccinated children. Fever from the MMR vaccine is usually around two weeks after the vaccine is given.

Some combinations of vaccines, when given together, have an increased risk of fever and febrile seizure than if they would be given on separate visits. Two of the most common combinations are the MMR and varicella (chicken pox) vaccine, as well as the pnemococcus and influenza vaccines.

In one particular study published in Pediatrics, the risk of febrile seizure  after MMR vaccine was found to be around 3.5 x higher than what would be considered the baseline risk. No significant increase in febrile seizures was seen after varicella vaccine alone, but when given simultaneously with the MMR vaccine, the risk increased slightly to 4x. Because this risk is still very low (remember we are talking somewhere a little above the range of 1-2 per thousand), it's generally very common to give the vaccines together, to avoid another poke for the child, although the varicella could be given at the 15 month visit and still be on schedule. Delaying the MMR vaccine until after 15 months, however, is actually associated with more febrile seizures.

There is also the MMRV vaccine, a combination measles, mumps, rubella and varicella vaccine in one poke. It's not preferred to give to infants because the risk of febrile seizure is significantly higher, around eight times the baseline risk, in children under the age of 4. It is not associated with increased febrile seizures in four-to-six year olds, which is great because the MMRV saves them an extra traumatic poke.

What about the flu shot? Most studies have not consistently found a strong increase in febrile seizures after influenza vaccination. However, a 2012 study found an increase in febrile seizures  when given at the same time as the pneumococcal vaccine, which prevents a bacterial infection that causes pneumonia and meningitis. The study found one additional febrile seizure for every 2,000 to 3,000 children vaccinated.

The pneumococcal vaccine is given at two, four, and six months of age, and again usually at 12-15 months. The influenza vaccine is for children six months and up. Both of these vaccines are pretty time sensitive (you don't want to miss any of the flu season unprotected, and infants are in a high risk period for pneumococcal disease). Because of this, I don't think it's a good idea to delay either vaccine to avoid the small risk of febrile seizure.

The upshot is, though a febrile seizure following vaccination is possible, the risk is small and they are not dangerous. They are far less common than febrile seizures from the diseases they prevent. For more information on febrile seizures, read:

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