Efficacy of vaccination against influenza in patients with multiple sclerosis: The role of concomitant therapies.

Multiple sclerosis is a chronic progressive demyelinating disease affecting over 2.1 million patients worldwide. Patients affected by MS are exposed to an increased risk of infection from communicable diseases, which may lead to severe disease relapses. Studies have analysed the issue of vaccination of MS-affected patients. These studies, however, deal mostly with safety-related issues documenting that most vaccines have been proven to be safe in MS patients and that vaccination is not associated with an increased risk of relapses. By contrast, evidence on the efficacy is comparatively scant and not yet systematised in a comprehensive picture. This aspect is however important, as both MS and its treatment alter the immune responses, a situation that may be associated with a reduced vaccine efficacy. We have now reviewed the literature and assessed the effects of the therapy for MS on vaccine efficacy; we focused on the vaccine against influenza as for the other vaccines the information is still too scant. The majority of drugs appear not associated with a reduced response to vaccination against influenza, with the notable exception of mitoxantrone and glatiramer acetate. For a few drugs, among which natalizumab, information is not sufficiently clear and additional studies are needed to draw a definite conclusion. These results highlight the importance to evaluate the efficacy of vaccination in patients treated with immunosuppressant drugs.