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The number of reported cases of Gillain-Barre syndrome (a rare paralytic disorder) that occur following influenza vaccination has decreased over the past 12 years, according to a study in the November 24 issue of JAMA.
Guillain-BarrÃ© syndrome (GBS) is a paralytic disorder in which the body's immune system affects part of the peripheral nervous system, according to background information in the article. The first symptoms include varying degrees of weakness or tingling sensations in the legs followed by progressive weakness. Concerns about the risk of developing GBS following influenza vaccination have been present since an association was first noticed during the 1976-1977 A/New Jersey ("swine influenza") season. Evidence for a relationship between GBS and other influenza vaccines, however, has been less clear. GBS remains the most frequent neurological condition reported after influenza vaccination to the Vaccine Adverse Events Reporting System (VAERS) since its inception in 1990.
Penina Haber, MPH, of the Centers for Disease Control and Prevention (CDC), Atlanta, and colleagues evaluated trends of reports to VAERS of GBS following influenza vaccination in adults. Reports of GBS in persons 18 years or older following influenza vaccination were evaluated for each influenza season from July 1, 1990, through June 30, 2003. The number of people vaccinated was estimated from the National Health Interview Survey and U.S. census data. Beginning in 1994, active follow-up was conducted to verify GBS diagnosis and obtain other clinical details.
The researchers found that from July 1990 through June 2003, VAERS received 501 reports of GBS following influenza vaccination in persons at least 18 years old. Annual reporting rates of GBS per 100, 000 influenza vaccinations declined from a high of 0.17 in 1993-1994 to a low of 0.04 in 2002-2003, a four-fold decrease. A GBS diagnosis was confirmed in 82 percent of reports. Preceding illness within 4 weeks of vaccination was identified in 24 percent of reported cases.
Reports of GBS had a different pattern of onset intervals from non-GBS reports, with the median onset interval for GBS reports (13 days) being longer than that of non-GBS reports after influenza vaccination (1 day). Fifty-nine percent of all GBS reports (n = 286) noted symptom onset within 0 to 14 days following vaccination, while 94.5 percent of all non-GBS reports noted symptom onset within the same time interval.
"The long onset interval and low prevalence of other preexisting illnesses are consistent with a possible causal association between GBS and influenza vaccine. These findings require additional research, which can lead to a fuller understanding of the causes of GBS and its possible relationship with influenza vaccine," the authors write.