Each year millions of children are vaccinated against measles , mumps , and rubella with the MMR vaccine. Although today’s vaccinations are extremely safe overall, research has shown that there is a slight increased risk of febrile seizures following the MMR vaccine.

Febrile seizures, which are characterized by a brief jerking or staring fit that is brought on by a high fever, are quite common: approximately one out of 25 children experience at least one such seizure during their childhood. And according to the Centers for Disease Control, about one out of 3,000 MMR vaccinations result in a febrile seizure. But whether the risk of seizures is linked to other factors—such as family history of seizures, birth weight, or socioeconomic status—is not known. Another unknown is the long-term outcome of these seizures.

A new study in the July 21, 2004 issue of the Journal of the American Medical Association found that children who received the MMR vaccination had almost three times the risk of having febrile seizures, than those who did not, but only during the two weeks following their immunization. Additionally, the long-term rate of epilepsy did not differ between the children who had febrile seizures after MMR vaccination and those whose febrile seizures stemmed from a different cause.

About the Study

This study included data on 537,171 children born in Denmark between January 1, 1991 and December 31, 1998, who were alive at three months. The researchers searched national databases to obtain the following information on each participant:

  • MMR vaccination status
  • History of febrile seizures and epilepsy – for both the participant and any siblings
  • Birth weight and duration of pregnancy
  • Socioeconomic status
  • Maternal education

The researchers followed the children through 1999 and compared incidences of febrile seizures between children who received the MMR vaccination and those who did not. They also compared the risk of seizure after vaccination among different subgroups of children, measured the recurrence of febrile seizures, and looked at whether or not a child went on to develop epilepsy.

The Findings

The 82% of children who received the MMR vaccination were 2.75 times more likely to experience a febrile seizure than those who were not vaccinated—but only during the two weeks following immunization, after this there was no difference in risk.

The greatest risk of seizure following MMR vaccination was among children with a history of febrile seizures. Siblings of children with a history of febrile seizures or epilepsy also had a slightly greater risk of seizure. Interestingly, the risk of seizure increased slightly with younger age of vaccination.

The researchers also found that children who experienced febrile seizures within two weeks of MMR vaccination had a 19% increased risk of recurrent febrile seizures, but no increased risk of epilepsy.

How Does This Affect You?

These findings are consistent with previous research showing that there is a slight, but increased risk of febrile seizures in children during the two weeks following MMR vaccination. However, these febrile seizures do not appear to be related to long-term risk of epilepsy. Additionally, this study suggests that the greatest risk factors for developing a febrile seizure after MMR vaccination are personal and family history of febrile seizures.

No previous study had calculated the difference in seizure risk depending on age at vaccination, and the results of this study suggest that further research is needed to determine whether age at vaccination affects the risk of seizure, as it appeared to in this study. The American Academy of Pediatrics currently recommends that all children receive the first of two doses of this vaccine between 12 and 15 months of age.

It’s important to note that febrile seizures, although scary to a parent, are usually harmless and not associated with long-term health effects. Thus when the risk associated with seizures is weighed against the risks associated with measles, mumps, and rubella, the MMR vaccine is the safer choice.

Although the risk associated with febrile seizures is low, just to be on the safe side parents should contact a healthcare provider if they think their child is having a febrile seizure. Additionally, some health care providers suggest giving children an aspirin-free pain reliever, such as Tylenol or Ibuprofen, at the first sign of a fever during the two weeks following MMR vaccination.