Guillain-Barré syndrome (GBS) is a rare autoimmune disorder, the incidence of which is estimated to be 0.6-4/100,000 person/year worldwide. Often, GBS occurs a few days or weeks after the patient has had symptoms of a respiratory or gastrointestinal microbial infection. The disorder is sub-acute developing over the course of hours or days up to 3 to 4 weeks. About a third of all cases of Guillain-Barré syndrome are preceded by Campylobacter jejuni infection. C. jejuni strains isolated from GBS patients have a lipooligosaccharide (LOS) with a GM1-like structure. Molecular mimicry between LOS and the peripheral nerves as a cause of GBS was demonstrated in animal models of human GBS. Following the "swine flu" virus vaccine program in the USA in 1976, an increase in incidence of GBS was observed and the calculated relative risk was 6.2. Later studies have found that influenza vaccines contained structures that can induce anti-GM1 (ganglioside) antibodies after inoculation into mice. More recent information has suggested that the occurrence of GBS after currently used influenza and other vaccines is rare. GBS involves genetic and environmental factors, may be triggered by infections or vaccinations, and predisposition can be predicted by analyzing some of these factors.