The measles, mumps, and rubella vaccination—popularly known as MMR—has turned those three diseases into stories to be heard at your grandmother's knee. But the vaccine itself has risks, too; some children have febrile seizures—convulsions with a high fever—after getting vaccinated. Fever is a common consequence of the vaccine. It would be helpful to know which children are likely to have seizures, and it's unclear whether post-MMR seizures make a child more likely to develop epilepsy. A group of Danish researchers followed every child born in the country to find out more about the association between the MMR vaccine and seizures.

What the researchers wanted to know: What children are more likely to have seizures after getting the MMR vaccine? Are those seizures likely to lead to epilepsy?

What they did: The researchers looked at data on every single child born in Denmark in 1991–1998 (at least, the ones who lived to be 3 months old); they followed more than 500,000 children using a national database of information on hospital visits.

What they found: Eighty-two percent of the children were vaccinated; 973 of them had a seizure within two weeks of the vaccination. There was no detectable increase for children who had a family history of epilepsy, for premature babies, low-income children, or any of a number of other variables the researchers looked for. Children who'd had a febrile seizure before were more likely to have a seizure after the MMR vaccination, but other than that, only children with siblings with epilepsy appeared to have a higher risk of seizure—an increase that wasn't statistically significant (there weren't enough children with such siblings). As for whether the seizures cause epilepsy, children who'd had one seizure were slightly more likely to have more seizures, but they did not have a higher risk of epilepsy.

What the study means to you: Unfortunately, they didn't find a way to predict which kids will have seizures after getting the MMR shot. But if they're right that febrile seizures don't increase a child's risk of getting epilepsy, that's good news.

Caveats: Since relatively few children in the study got epilepsy, it's hard to be really definite about the risk of that disease.

Find out more: The CDC's site on MMR

Read the article: Vestergaard, M., Hviid, A., Madsen, K.M., Wohlfahrt, J., Thorsen, P., Schendel, D., Melbye, M., and J. Olsen. "MMR Vaccination and Febrile Seizures." Journal of the American Medical Association. July 21, 2004, Vol. 292, No. 3, pp. 351–357.

Abstract online: http://jama.ama-assn.org