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. 
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 . 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).