title: Observational safety study of febrile convulsion following first dose MMRV vaccination in a managed care setting.
abstract: BACKGROUND
  A combined measles, mumps, rubella, varicella live vaccine (MMRV, Merck and Co., Inc., US) was recently licensed in the US. Pre-licensure clinical trial data showed a significant increase in fever in days 5-12 following MMRV vaccination as compared to the vaccines given separately (MMR+V). This post-licensure retrospective cohort study was undertaken to assess the incidence of febrile convulsion following MMRV.
  
  
  METHODS
  Children ages 12-60 months who received a first dose of MMRV in February 2006-June 2007 in a managed care organization were included in the study. Subjects were optimally matched on age, sex, and calendar date of vaccination to children who received MMR+V concomitantly in November 2003-January 2006, before MMRV licensure. Potential cases of febrile convulsion were identified through administrative data and adjudicated by expert panel, according to pre-specified criteria.
  
  
  RESULTS
  During the 30 days post-vaccination, there were 128 and 94 potential convulsion cases among the 31,298 children in the MMRV and MMR+V cohorts, respectively. After review of available medical charts and adjudication, there were 84 cases of confirmed febrile convulsion, 44 (1.41/1000) and 40 (1.28/1000) in the MMRV and MMR+V cohorts, respectively (RR=1.10, 95% CI=0.72, 1.69). In days 5-12 following vaccination, a pre-specified period of interest, the respective numbers were 22 (0.70/1000) and 10 (0.32/1000) (RR=2.20, 95% CI=1.04, 4.65).
  
  
  CONCLUSIONS
  These data suggest that the risk of febrile convulsion is increased in days 5-12 following vaccination with MMRV as compared to MMR+V given separately during the same visit, when post-vaccination fever and rash are also increased in clinical trials. While there was no evidence of an increase in the overall month following vaccination, the elevated risk during this time period should be communicated and needs to be balanced with the potential benefit of a combined vaccine.
authors.affiliation: Department of Research and Evaluation, Kaiser Permanente Southern California, Pasadena, CA 91101, USA. steven.j.jacobsen@kp.org
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Jacobsen
authors.forename: Bradley K
authors.initials: BK
authors.lastname: Ackerson
authors.forename: Lina S
authors.initials: LS
authors.lastname: Sy
authors.forename: Trung N
authors.initials: TN
authors.lastname: Tran
authors.forename: Tonia L
authors.initials: TL
authors.lastname: Jones
authors.forename: Janis F
authors.initials: JF
authors.lastname: Yao
authors.forename: Fagen
authors.initials: F
authors.lastname: Xie
authors.forename: T Craig
authors.initials: TC
authors.lastname: Cheetham
authors.forename: Patricia
authors.initials: P
authors.lastname: Saddier
mesh_terms: D019433:Chickenpox Vaccine / Q000009:adverse effects*; D002675:Child, Preschool; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D008297:Male; D008329:Managed Care Programs; D022542:Measles-Mumps-Rubella Vaccine / Q000009:adverse effects*; D012189:Retrospective Studies; D003294:Seizures, Febrile / Q000209:etiology*; D013997:Time Factors; D014481:United States; D017778:Vaccines, Combined
chemical_list: D019433:Chickenpox Vaccine; D022542:Measles-Mumps-Rubella Vaccine; D017778:Vaccines, Combined; C050102:measles, mumps, rubella, varicella vaccine