The vaccine for measles, mumps, rubella and chicken pox is not associated with an increased risk of febrile seizures — brief convulsions that can occur during a high fever — in children four to six years old, new research suggests.

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There's reassuring evidence that vaccines against measles don't increase the risk of brief convulsions that can occur during a high fever, researchers say. (Beawiharta Beawiharta/Reuters)

The U.S. study looked at the risk of febrile seizures among nearly 67, 500 children who received an older version of the measles, mumps, rubella (MMR) vaccine followed by the varicella or chicken pox shot the same day. The febrile seizure risk was compared with another group of 86,750 children who received a newer version of the vaccine, called MMRV, that combines all four inoculations in one shot.

The U.S. Centers for Disease Control and Prevention funded the research in Monday's issue of the journal Pediatrics to evaluate the risk of febrile seizures in preschoolers following an earlier study that pointed to an increased risk of the convulsions among babies and toddlers receiving MMR or MMRV.

The newer version containing all four is available in Canada.

The researchers found there was no increased risk of febrile seizures, most of which don't require treatment, in either group of four- to six-year-olds who received the vaccines between 2000 and 2008.

"There was one febrile seizure seven to 10 days after MMRV and none after [the older version]," reads the study.

The researchers conclude there is no increased risk of febrile seizures in either group.

"The results provide reassuring evidence that neither MMRV, nor MMR plus V, appear to be associated with an increased risk of post-vaccination febrile seizures in this four-to-six age group," said lead author Dr. Nicola Klein, co-director of the Kaiser Permanente Vaccine Study Center, in a release.

"As febrile seizures are generally much less likely to occur among four- to six-year-old children, it is  probably not too surprising that we did not detect increased febrile seizures," after vaccination, reads the study.

Combo vaccine available in Canada

The research follows an earlier study that found that among one- to two-year-olds, the risk of febrile seizures seven to 10 days after MMRV was double that of MMR plus V.

In Canada, MMRV was approved for use in December 2007, where it is sold by GlaxoSmithKline as Priorix-Tetra. On its website, the Public Health Agency of Canada states that unlike ProQuad, made by Merck, Priorix-Tetra has not been identified as posing a risk of febrile seizure.

"The rate of febrile seizures after the administration of the GSK's MMRV vaccine, Priorix-Tetra has not been reported to be higher when compared with MMR plus V administered separately," reads PHAC's website. 

"This is in spite of the observed higher rate of fever [greater than or equal to 38 C, although not for greater than or equal to 39.5 C] after the first dose of MMRV in children under two years of age."