Seasonal flu vaccine and Guillain-Barre: no correlation!
I spotted this article in the Health Section of the New York Times; an extensive retrospective study published in the journal Clinical Infectious Diseases has found no correlation between receiving the seasonal influenza vaccine and developing the serious neurological condition Guillain-Barré Syndrome (GBS). This finding gave me great joy, and also gives me an opportunity to link back to one of my favorite Rage Stroke®-inducing BIO230 postings. The possibility for correlation arose from the 1976 Swine flu vaccine, in which the Centers for Disease Control and Prevention reported a slightly increased risk for developing GBS following receiving that vaccine, with the risk being approximately 1 case of GBS per 100,000 vaccine doses. This measurable increase led to a moratorium and reformulation of the vaccine.
An extensive investigation by the Institutes of Medicine (IOM) confirmed the increased risk of developing GBS with the 1976 influenza vaccine, and although several theories were put forth to explain the potential correlation, the cause remains unclear. One possibility hypothesized in the IOM study linked above suggests that the clear association between developing GBS and infection with the bacterium Campylobacter jejuni might be to blame. Campylobacter is an ubiquitously distributed organism, however it does infect chickens, and eggs are used to produce the influenza virus used to produce the vaccine. The increased incidence of GBS with that year’s vaccine therefore might have been due to contaminating Campylobacter antigens present in the killed vaccine preparation.
The study described in the New York Times article recounts an extensive retrospective analysis of patients from a California health care system, and data examined covered more than 30 million person-years worth of medical records. In that data set, 415 cases of Guillain-Barré were observed for a total annual incidence of approximately 1 in 90,000 people in the population, a number that is very much in line with what is reported by the CDC. Out of those 415 confirmed cases, 25 of them had a reported influenza vaccine in the 6 weeks prior to developing GBS symptoms. Most of the cohort had received a flu vaccine at some point in their medical history, but had additionally had a large variety of other vaccines. The researchers recognize that the very limited number of GBS cases in relation to the large number of records examined limits the statistical power of their analysis, however no apparent correlation between first receiving a seasonal influenza vaccine and then developing GBS could be demonstrated. The researchers further affirm that during the 1976 outbreak there was a causal link between the swine flu vaccine and developing GBS, but as vaccine formulations have been modified, no further link exists. The much more likely culprit causing Guillain-Barré Syndrome is an underlying infection, most likely due to Campylobacter, which can be easily prevented by properly cooking food and washing your hands.