Prognostic factors in multiple sclerosis: role of intercurrent infections and vaccinations against influenza and hepatitis B.

Since the first historical description of multiple sclerosis (MS) it has been known that febrile illnesses frequently trigger relapses of the disease. In spite of this knowledge, vaccination against influenza has been hampered for a long period by neurologists on the basis of anecdotal cases of post-vaccination encephalomyelitis. Randomized, double-blind, placebo-controlled studies during the past decade have shown that influenza vaccination of MS patients neither increases the relapse rate nor worsens the course of the disease. In contrast, the reduction of viral infection episodes leads to a lower number of exacerbations of MS. Influenza vaccination is safe and should be recommended to MS patients in order to avoid attacks of the disease. After publication of case reports of hepatitis B (HB) vaccination followed by onset of MS, a media-driven scare campaign mainly in France was conducted. The French health authorities decided to suspend routine vaccination of adolescents in schools, invoking the "principle of precaution". This fact has caused widespread confusion and concern about the HB vaccination. Epidemiological studies in large populations have recently been performed to investigate a possible link between HB vaccination and MS: all results argue against a causal relation between HB vaccine and MS or other demyelinating diseases. Since the vaccination provides complete protection against hepatitis B and its severe long-term complications, the World Health Organization recommends continuing the implementation of the HB vaccination programs.