Study designs of evaluations included in the review
Case-control and cohort studies were eligible for inclusion. All of the included studies were case-control studies; some were nested case-control studies.
Specific interventions included in the review
Studies that attempted to ascertain vaccinations for the period before the diagnosis of MS were eligible for inclusion. Most of the included studies ascertained vaccination status by self-report; others used computerised records. Exposure period of vaccination, where reported, ranged from lifetime exposure to less than 3 years before the diagnosis of MS; however, most studies did not specify the exposure period. The studies were conducted in six countries.
Participants included in the review
Studies of patients with a physician-confirmed diagnosis of MS were eligible for inclusion. Comparator groups were hospital patients, the general population, patients with other neurological diseases, blood donors, friends and relatives.
Outcomes assessed in the review
Studies had to report a measure of association between tetanus vaccination and the incidence of MS, along with its 95% confidence interval (CI), or sufficient data to calculate these data, to be eligible for inclusion.
How were decisions on the relevance of primary studies made?
The authors did not state how the papers were selected for the review, or how many reviewers performed the selection.