Side effects following vaccination in multiple sclerosis: a prospective, multi-centre cohort study.

Vaccines play a crucial role in preventing infections in patients with multiple sclerosis (MS), although concerns have been raised about potential worsening of the underlying disease. To investigate this, we conducted a prospective, multicentre, non-randomized observational study assessing changes in disease activity, safety, and clinical tolerability of vaccination in 222 MS patients on disease-modifying drugs. The majority of patients were female (76.6%) and 89.6% had relapsing-remitting MS. The vaccines administered were primarily seasonal influenza (56.3%) or tetanus-based vaccines (33.8%). Disease activity, as measured by annualized relapse rate, decreased significantly from 0.64 the year prior to vaccination to 0.38 in the following year. Moreover, the extended disability status scale remained stable within six months after vaccination in comparison to pre-vaccination values. Side effects were reported in 19.2% of vaccinated subjects, most commonly local side effects (65.2%) or flu-like symptoms (34.8%). Our findings suggest that standard non-live vaccines are safe and well-tolerated in MS patients and do not negatively impact disease activity.