Tetravalent Influenza Vaccine Is Not Associated With Neuroaxonal Damage in Multiple Sclerosis Patients.

Background: Efficacy of vaccines and disease activity linked to immunization are major concerns among people with multiple sclerosis (pwMS). Objective: To assess antibody responses to seasonal influenza antigens and vaccine-associated neuroaxonal damage utilizing serum neurofilament light chain (sNfL) in pwMS receiving dimethyl fumarate (DMF). Methods: In this prospective study, the 2020/2021 seasonal tetravalent influenza vaccine was administered to 20 pwMS treated with DMF and 15 healthy controls (HCs). The primary endpoints were responder rate of strain-specific antibody production (seroconversion or significant (4-fold) increase in influenza-antibody titers for ≥2/4 strains) at 30 days post-vaccination and changes in sNfL levels. Results: All patients treated with DMF fulfilled the responder criteria for immunization compared with 53% of the controls. However, higher proportions of HCs already had influenza-antibody titers ≥1:40 at baseline (53% vs. 41%, p = 0.174). sNfL levels were comparable among both groups at baseline and did not increase 34 days after vaccination. In addition, no clinical or radiological disease reactivation was found. Conclusion: DMF-treated patients mount an adequate humoral immune response to influenza vaccines. Within the limits of the small cohort investigated, our data suggest that influenza immunization is not associated with clinical or subclinical disease reactivation.