Hepatitis B vaccination and first central nervous system demyelinating events: Reanalysis of a case–control study using the self-controlled case series method

The hypothesis that hepatitis B vaccination is a risk factor for multiple sclerosis has been discussed at length. The data from an earlier case–control study were reanalyzed using the self-controlled case series method. Using the matched cases from the case–control study, we found a relative incidence of 1.68, 95% CI (0.77–3.68) for the 0–60-day post-vaccination risk period; this compares to an odds ratio of 1.8, 95% CI (0.7–4.6). When an additional 53 unmatched cases not used in the case–control study were included, the relative incidence was 1.35, 95% CI (0.66–2.79). Our results throw further light on the methodological aspects of the case series method. We recommend that, when case–control studies of vaccination and adverse events are planned, case series analyses based on the cases are also undertaken when appropriate.