Patients are not at increased risk of Guillain-Barré syndrome in the six-week period after receiving any vaccine, including influenza, according to a study.
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, Roger Baxter, MD, the studys lead author and co-director of the Kaiser Permanente Vaccine Study Center, said in a news release.
During the 13-year period (1994-2006), 415 confirmed cases of Guillain-Barré syndrome were observed. Within this group, only 25 patients had received any vaccine in the six weeks prior to onset of the disease, while 277 patients had a respiratory or gastrointestinal illness in the 90 days preceding onset.
In the study sample, the researchers reported, the risk of developing Guillain-Barré syndrome within six weeks of receiving any vaccine was not notably higher than during the previous nine to 12 months.
Guillain-Barré syndrome had been linked to the influenza vaccine in a 1976 study, but not clearly since, according to background information for the new study, which will be published in the July 15 issue of the journal Clinical Infectious Diseases. Reports of an association with other vaccines 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 that may be unmeasured, Baxter said.
The researchers further explained that variables that change over time such as 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 focused on the outcome, then looked 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, the researchers said.
Read the study abstract: http://cid.oxfordjournals.org/content/57/2/197.abstract.