Study to Investigate the Immune Response to Influenza Vaccine in Patients With Multiple Sclerosis on Teriflunomide

Primary Objective: Assess the antibody response to influenza vaccine in patients with relapsing form of multiple sclerosis (RMS) treated with teriflunomide compared to a reference population. Secondary Objectives: * Assess the effect of teriflunomide on immunoglobulin levels; * Assess the safety of influenza vaccination in patients with RMS treated with teriflunomide. The reference population was defined as multiple sclerosis (MS) patients with a stable treatment with interferon-β-1. Antibody response was measured using hemagglutination inhibition assay (HIA) and the hemagglutinin antigens representing the stains of H3N2, H1N1, and B as present in the influenza vaccine used.