Antibody response elicited by the SARS‐CoV‐2 vaccine booster in patients with multiple sclerosis: Who gains from it?

Abstract Background and purpose Although two doses of COVID‐19 vaccine elicited a protective humoral response in most persons with multiple sclerosis (pwMS), a significant group of them treated with immunosuppressive disease‐modifying therapies (DMTs) showed less efficient responses. Methods This prospective multicenter observational study evaluates differences in immune response after a third vaccine dose in pwMS. Results Four hundred seventy‐three pwMS were analyzed. Compared to untreated patients, there was a 50‐fold decrease (95% confidence interval [CI] = 14.3–100.0, p < 0.001) in serum SARS‐CoV‐2 antibody levels in those on rituximab, a 20‐fold decrease (95% CI = 8.3–50.0, p < 0.001) in those on ocrelizumab, and a 2.3‐fold decrease (95% CI = 1.2–4.6, p = 0.015) in those on fingolimod. As compared to the antibody levels after the second vaccine dose, patients on the anti‐CD20 drugs rituximab and ocrelizumab showed a 2.3‐fold lower gain (95% CI = 1.4–3.8, p = 0.001), whereas those on fingolimod showed a 1.7‐fold higher gain (95% CI = 1.1–2.7, p = 0.012), compared to patients treated with other DMTs. Conclusions All pwMS increased their serum SARS‐CoV‐2 antibody levels after the third vaccine dose. The mean antibody values of patients treated with ocrelizumab/rituximab remained well below the empirical "protective threshold" for risk of infection identified in the CovaXiMS study (>659 binding antibody units/mL), whereas for patients treated with fingolimod this value was significantly closer to the cutoff.