Vaccines don't cause Guillain-Barre Syndrome (GBS), concludes a study of millions of patients at Kaiser Permanente facilities in northern California. Just 415 cases of GBS were confirmed in medical records from 1994 to 2006, and only 25 of those 415 people had received any kind of immunization within six weeks before the onset of symptoms. Slightly more men than women developed GBS, and GBS was 50% more likely to occur in winter than summer months. Two-thirds of all people with GBS had had a respiratory or gastrointestinal infection within the 90 days preceding GBS onset. The results "provide reassurance that the risk of GBS following any vaccination, including influenza vaccines, is extremely low," conclude the authors in Clinical Infectious Diseases (published online May 10).