The retrospective study by researchers at the Kaiser Permanente Vaccine Study Center spanned 13 years and was controlled for seasonality.
“If there is a risk of Guillain-Barré syndrome following any vaccine, including influenza vaccines, it is extremely low,” said Roger Baxter, MD, co-director of the Kaiser Permanente Vaccine Study Center.
During the 13-year period (1994 to 2006), 415 confirmed cases of Guillain-Barré syndrome were observed. Within this group, the researchers found only 25 patients had received any vaccine in the six weeks prior to the onset of the disease. The study also found that 277 patients had a respiratory or gastrointestinal illness in the 90 days preceding the onset.
Guillain-Barré syndrome is an acute disease thought to be an autoimmune disorder resulting in destruction of a nerve’s myelin sheath and peripheral nerves. In many cases, the syndrome is temporally associated with an infectious disease; most published case series report that approximately two-thirds of all cases are preceded within three months by a gastrointestinal or respiratory infection. Guillain-Barré syndrome had been linked to the influenza vaccine in a 1976 study, but not clearly since. There have been reports of an association with other vaccines, which have not been confirmed.
Previous studies of Guillain-Barré syndrome as a possible adverse event related to vaccines have been subject to confounding by differences between vaccinated and unvaccinated individuals which may be unmeasured, said Dr. Baxter, who led the team that conducted this new research.
The Vaccine Study Center researchers further 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. For this reason, they said, it is necessary to use special epidemiologic and statistical methods to overcome these variables.
The case-centered study design used to conduct this research focuses on the outcome, then looks back to determine vaccination status. This method can control for many of the variables that change over time and, consequently, lead to a more accurate assessment of Guillain-Barré syndrome risk or recurrence following vaccination.
Additional authors on the study include Nicola P. Klein, MD, PhD, Bruce Fireman, MA, Paula Ray, MPH, and Edwin Lewis, MPH, with the Kaiser Permanente Vaccine Study Center; Nandini Bakshi, MD, with The Permanente Medical Group; and Claudia Vellozzi, MD, MPH, with the Immunization Safety Office, Centers for Disease Control and Prevention.
About the Kaiser Permanente Vaccine Study Center
FFounded in 1985, the Kaiser Permanente Vaccine Study Center began as a way of responding to numerous requests to use Kaiser Permanente’s large population for vaccine efficacy studies. Key studies have focused on Haemophilus influenza, type B (Hib), chickenpox, pneumococcus, rotavirus and flu vaccines. The center operates 31 sites in Northern California and collaborates with Kaiser Permanente’s Northwest, Hawaii and Colorado regions, as well as participates in several Centers for Disease Control and Prevention and National Institutes of Health studies. For more information, visit www.dor.kaiser.org/external/DORExternal/vsc/index.aspx.
About the Kaiser Permanente Division of Research
The Kaiser Permanente Division of Research conducts, publishes and disseminates epidemiologic and health services research to improve the health and medical care of Kaiser Permanente members and the society at large. It seeks to understand the determinants of illness and well-being and to improve the quality and cost-effectiveness of health care. Currently, DOR’s 600-plus staff is working on more than 250 epidemiological and health services research projects. For more information, visit www.dor.kaiser.org.
About Kaiser Permanente
Kaiser Permanente is committed to helping shape the future of health care. We are recognized as one of America’s leading health care providers and not-for-profit health plans. Founded in 1945, our mission is to provide high-quality, affordable health care services and to improve the health of our members and the communities we serve. We currently serve more than 9.1 million members in nine states and the District of Columbia. Care for members and patients is focused on their total health and guided by their personal physicians, specialists and team of caregivers. Our expert and caring medical teams are empowered and supported by industry-leading technology advances and tools for health promotion, disease prevention, state-of-the-art care delivery and world-class chronic disease management. Kaiser Permanente is dedicated to care innovations, clinical research, health education and the support of community health.