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Scientists have found no evidence that vaccines increase the risk of Guillain-Barré syndrome.

New research revealed no evidence that patients are at an increased risk of Guillain-Barré syndrome in the six-week period after vaccination with any vaccine, including influenza.

Guillain-Barré syndrome, which is an acute disease believed to be an autoimmune disorder, can result in destruction of a nerve's myelin sheath and peripheral nerves.  The syndrome is sometimes temporally associated with an infectious disease.  Recent studies revealed that around two-thirds of all cases are preceded within three months by a gastrointestinal or respiratory infection. Researchers said that Guillain-Barré syndrome had been linked to the influenza vaccine in a 1976 study.  However, newer studies have failed to find a clear link between vaccines and the disease. While there have been reports of an association with other vaccines, those findings have not been confirmed, according to researchers.

In the recent study published in the journal Clinical Infectious Diseases, researcher Dr. Roger Baxter, co-director of the Kaiser Permanente Vaccine Study Center, looked at 415 confirmed cases of Guillain-Barré syndrome between 1994 and 2006.  Within this group, researcher found that only 25 patients had received any vaccine in the six weeks prior to the onset of the disease.  Baxter and his team also found that 277 patients had a respiratory or gastrointestinal illness in the 90 days preceding the onset.

Researchers noted that previous studies of Guillain-Barré syndrome as a possible side effect related to vaccines have been subject to confounding by differences between vaccinated and unvaccinated individuals which may be unmeasured.

They explained that variables that change over time, like infectious diseases or rates of vaccination, can lead to confusion in observational studies which look at already collected data rather than randomizing people to treatment versus placebo.  Because of these factors, researchers said it is necessary to use special epidemiologic and statistical methods to overcome these variables

The latest study, which focuses on the outcome and then looks back to determine vaccination status, can control for many variables that change over time.  The latest findings from the study, which researchers say leads to a more accurate assessment of Guillain-Barré syndrome risk or recurrence following vaccination, found no evidence of increased risk of Guillain-Barre syndrome following vaccination, researchers concluded.