Risk of breakthrough COVID-19 after vaccination among people with multiple sclerosis on disease-modifying therapies

Disease-modifying therapies (DMTs) for people with multiple sclerosis (pwMS) may decrease vaccine effectiveness. We aimed to explore the association between various DMTs and the risk for breakthrough COVID-19.

Population-based data from Clalit Health Services, Israel's largest healthcare organization, were used. PwMS treated with DMTs without prior COVID-19 were followed from the commencement of the mass vaccination campaign in December 2020. The end of follow-up was at the time of COVID-19 infection, the receipt of a third vaccine dose or until the end of August 2021. Time-dependent multivariate Cox proportional hazard models were used to estimate hazard ratios for COVID-19 according to vaccination, DMT, age, gender, disability and comorbidities.

2511 PwMS treated with DMTs were included (Age: 46.2 ± 14.6, 70% Female, EDSS: 3.0 ± 2.1). Of whom, 2123 (84.5%) received 2 vaccine doses. On multivariate models that included all pwMS, vaccination was protective (HR = 0.41, P < 0.001). On multivariate models that included only fully vaccinated pwMS cladribine, ocrelizumab, S1P receptor modulators and natalizumab were associated with breakthrough COVID-19 (HR = 6.1, 4.7, 3.7 and 3.3; P = 0.004, 0.008, 0.02 and 0.05, respectively). On multivariate models that included unvaccinated and fully vaccinated pwMS on each DMT separately, a protective trend was noted for vaccination on all DMTs (0.09 < HR < 0.65), except for cladribine (HR = 1.1). This protective trend was not statistically significant on ocrelizumab, S1P receptor modulators and natalizumab. COVID-19 among pwMS was generally mild. Only 2 vaccinated pwMS had a severe infection with eventual recovery.

Vaccination effectively protects pwMS from COVID-19. An increased risk of breakthrough infection was noted on high-efficacy DMTs, however COVID-19 after vaccination was usually mild.