Researchers from the Kaiser Permanente Vaccine Study Center, Oakland, CA, other centers in the US, and Centers for Disease Control and Prevention, Atlanta. GA, using 2000-2008 Vaccine Safety Datalink data, compared the risk of febrile seizures among children aged 12 to 23 months after MMRV and separate MMR + varicella vaccines. Analyses included Poisson regression and supplementary regressions incorporating chart-review results. Seizure and fever incidence significantly peaked 7 to 10 days after vaccination with all measles-containing vaccines but not after varicella vaccination alone. The relative risk of seizures was 7.6 (P<0.0001) after MMRV combined vaccination, 4.0 (P<0.0001) after MMR + varicella separate vaccinations, and 3.7 (P<0.0001) after MMR vaccination alone. No seizure peak occurred after varicella vaccination alone. Rates for seizures during days 7 to 10 were 84.6/1000 person-years after MMRV, 42.2 seizures per 1000 person-years after MMR + varicella, and 26.4/1000 after MMR alone. Unadjusted rates were 8 times higher for MMRV and 4 and 3.5 times higher for MMR + varicella and MMR vaccination alone, respectively. Outpatient fever visits sharply increased during days 7 to 10, most actively after MMRV. The proportion of children with post-vaccination febrile seizures with a history of seizures was similar for MMRV (16%) and MMR + varicella vaccines (22%) [P=0.21]. Of those with febrile seizures, family history was positive for seizures among 30% of MMRV recipients vs 29% of MMR + varicella vaccines (P=0.90). The use of MMRV vaccine instead of separate MMR + varicella vaccines approximately doubles the risk for fever and febrile seizures. Providers who use the combination vaccine should notify parents of this increased risk of febrile seizures. [1]

COMMENT. The risk of fever and febrile seizures is increased 7 to 10 days following all measles-containing vaccines, and the risk after the combination MMVR vaccine is double that associated with separate MMR + varicella vaccines. Varicella vaccine alone does not increase febrile seizure risk.

Diphtheria-tetanus acellular pertussis vaccine (DTaP) in children aged 6 weeks to 23 months showed no increased risk of seizures within 0 to 3 days after vaccination, in a retrospective study from 1997 through 2006 conducted by 7 managed care organizations and the Vaccine Safety Datalink Team using risk-interval cohort and self-controlled case series analyses [2]. By contrast published studies report a relative risk of 3.3 for febrile seizures within 0-3 days of DTP whole-cell pertussis vaccine (RR 5.7 on the same day as vaccination). [3]