Rabies vaccination and multiple sclerosis relapse: A retrospective cohort study

•Safety data on rabies vaccination in persons with multiple sclerosis (MS) are lacking.•It is unknown whether MS patients have an increased for relapse after RV.•A self-controlled retrospective cohort of 55 MS patients was followed in the year before and the year after prophylactic RV.•There were fewer relapses in the year after vaccination, including the three-month post-vaccination exposure period, than in the year before.•Rabies vaccination was not associated with MS relapse. No studies assessing rabies vaccine (RV) tolerability in persons with multiple sclerosis (MS) have been conducted. Given the lack of safety data, RV is recommended essentially only for post-exposure prophylaxis, which is difficult to administer effectively in many rabies-endemic countries. We sought to determine whether RV administration as pre-exposure prophylaxis was associated with MS relapse. This retrospective cohort study compared the clinical courses of MS patients in the year before and after rabies vaccination. The year before vaccination was defined as the pre-exposure risk period, the three months thereafter as the exposure-risk period, and the following nine months as the post-risk period. All adult MS patients immunized with RV between 2014 and 2018 and with available medical records in the two-year window were included. The primary outcome was the incidence of symptomatic MS relapse in the exposure-risk period versus the pre-exposure period. Fifty-five patients received at least one dose of RV. Most (38/55, 69%) were female; mean age was 38.5 years (SD ±9.2). While 21 (38%) patients experienced 24 relapses in the year before vaccination, only three (5%) experienced one relapse each in the post-vaccination exposure-risk period; three others (5%) experienced a total of four relapses in the subsequent post-risk period. The annualized relapse rates in the pre-exposure, exposure-risk, and post-risk periods were 0.44, 0.22, and 0.10, respectively (rate ratio for exposure-risk to pre-exposure periods, 0.509 [95% CI 0.098–1.677]). In this cohort, rabies vaccination was not associated with clinical MS relapse. Larger, prospective studies are needed to confirm these results.