Impact of history of febrile convulsions on the risk difference of febrile convulsions with the tetravalent measles-mumps-rubella-varicella vaccine: Post-hoc exploratory analysis of results from a matched-cohort study.

This post-hoc analysis of data from a matched cohort study investigated the risk of febrile convulsions (FC) 5-12 days post-first dose of measles-mumps-rubella-varicella vaccine (MMRV) in a low-risk population, compared to measles-mumps-rubella (MMR) and varicella (V) vaccines administered separately. The low-risk population excluded children with personal history of FC (Scenario 1) and children with personal or/and family history (≥1 parent/sibling) of FC (Scenario 2). Incidence of FC post-MMRV in Scenario 2 (excluding at risk children) (36.3-49.5/100,000) and post-MMR+V in the whole cohort including children with personal/family history of FC (43.6/100,000) were similar. The risk difference of FC increased by 0.2 case/100,000 in Scenario 1 and decreased by 5.3-8.6 cases/100,000 of vaccinated children in Scenario 2, compared to the whole cohort. The overall risk of FC post-first dose MMRV vaccination could be lowered by administering MMRV only to children with no personal or family history of FC.