Tetanus vaccination and risk of multiple sclerosis: a systematic review.

OBJECTIVE To conduct a systematic review on the association between tetanus vaccination and the risk of multiple sclerosis (MS). METHODS The authors searched the databases Medline, LILACS, EMBASE, and Science Citation Index including the period 1966 to September 1, 2005. Eligible studies had to meet the following inclusion criteria: presentation of original data, case-control or cohort design, physician-confirmed diagnosis of MS as the outcome of interest, attempt to ascertain vaccinations in a period before the diagnosis, and report of an association measure between tetanus vaccination and incidence of MS, and its 95% CI or enough information to compute it. Study specific log ORs were weighted by the inverse of their variances to obtain a pooled estimate and its 95% CI. RESULTS The OR of MS associated with history of tetanus vaccination was 0.67 (95% CI: 0.55 to 0.81). There was little indication of heterogeneity of results across studies. CONCLUSION Tetanus vaccination is associated with a lower risk of multiple sclerosis.