Vaccination with combination measles-mumps rubella-varicella (MMRV) vaccine or separate measles-mumps-rubella (MMR) and varicella vaccines does not increase the risk for febrile seizures among 4- to 6-year-olds, results of a large cohort study indicate.

“This study provides reassurance that MMRV and separately administered MMR and varicella vaccines were not associated with increased risk of febrile seizures among 4- to 6-year olds,” Nicola P. Klein, MD, PhD, of the Kaiser Permanente Vaccine Study Center in Oakland Calif., and colleagues reported in Pediatrics.

The researchers examined risk for febrile seizures among this age group, after previous studies showed that MMRV vaccine doubled the risk for febrile seizures in the seven to 10 day after immunization in younger children aged 12- to 23-months, compared with those administered the MMR and varicella shots separately but on the same day.

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Due to these findings, current CDC recommendations favor vaccinating younger infants with separate MMR and varicella vaccines in lieu of the combined MMRV vaccine.

The current study involved more than 150,000 children who were vaccinated from 2000 to 2008 — 86,750 of whom were vaccinated with MMRV and 67,438 of whom received separate MMR plus varicella vaccines.

Using ICD-9 codes, the researchers confirmed just one febrile seizure with 86,750 MMRV doses. Furthermore, there were no seizures in the 67,000 who received the MMR and varicella vaccines separately but on the same day.

“We can rule out with 95% confidence a risk greater than one febrile seizure per 15,500 MMRV doses and one per 18,000 MMR + V doses,” the researchers wrote.

These study findings are consistent with existing data from both pre- and post-licensure safety studies in 4- to 6-year olds, that indicate the risk for febrile seizure with the MMRV, and the MMR and varicella vaccines, drops off as children get older.

Febrile seizures cause no long-term harm, and can be caused by ear infections, colds and other viral illnesses, the researchers added. They occur in about 5% of all children aged 5 years and younger, and peak around 18 months of age.

Klien NP et al. Pediatrics. 2012;129:1-6.