Oakland, Calif. – In a large, retrospective study, using a new methodology that controls for seasonality, researchers did not find evidence of an increased risk of Guillan-Barre Syndrome (GBS) in the six week period after vaccination — with any vaccine, including influenza.
Researchers from the Kaiser Permanente Vaccine Study Center also examined confirmed cases of GBS over many years to determine whether vaccination was associated with recurrence of GBS. They found no evidence that vaccination is associated with GBS recurrence.
The research is being presented this week at the 49th Annual Meeting of the Infectious Disease Society of America held in Boston, MA.
Guillain-Barré syndrome (GBS) is an acute disease thought to be an autoimmune disorder and has been reported following these vaccines: rabies, combined diphtheria and tetanus, hepatitis B, influenza, and meningococcal conjugate vaccines.
The Current CDC recommendation is to avoid vaccinating people who have had a history of GBS within six weeks of a prior influenza vaccination if they are not at high risk of severe complications from the flu.
Previous studies of GBS as a possible adverse event related to vaccines have been subject to confounding by differences between vaccinated and unvaccinated individuals which may be unmeasured, explained Roger Baxter, MD, co-director of the Northern California Kaiser Permanente Vaccine Study Center who led the team that conducted this new research.
The Vaccine Study Center researchers further explain 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 vs. placebo. For this reason, they said, it is necessary to use special epidemiologic and statistical methods to overcome these confounding variables.
A new methodology, identified by researchers at the Kaiser Permanente Vaccine Study Center and used to conduct the research being presented this week, focuses on the outcome, then looks back to determine vaccination status. The researchers explain that this method can control for many of the variables that change over time and, consequently, the method leads to a more accurate assessment GBS risk or GBS recurrence following vaccination.
Researchers identified GBS cases from the Kaiser Permanente Northern California (KPNC) databases from 1995 into 2006, using hospital discharge codes; each medical record was neurologist-reviewed and only confirmed GBS cases were included for follow up. They followed confirmed cases through 2008 for vaccinations and recurrences of GBS.
Additional researchers include: Nicky Klein, MD, PhD; Ned Lewis, MPH; and Paula Ray, MPH, with the Kaiser Permanente Vaccine Study Center; and Bruce Fireman with the Kaiser Permanente Division of Research. The research was funded by the Centers for Disease Control and Prevention, Atlanta, GA.