Reports of Rare Syndrome After Flu Shot Drop
Fewer Guillain-Barré Syndrome Cases Reported After Flu Vaccine
Nov. 23, 2004 -- The risk of a rare immune system disorder following a flu shot appears to be decreasing, a new study shows.
Researchers found the number of cases of Guillain-Barré syndrome that has occurred following vaccination with a flu shot has decreased dramatically during the last 12 years.
Guillain-Barré syndrome is a rare nervous system disorder in which the body's immune system attacks part of the nervous system. This immune system malfunction is usually triggered by an infection or other illness. Guillain-Barré usually occurs a few days or weeks after symptoms of a respiratory or stomach viral infection. Occasionally, surgery or vaccinations will trigger the syndrome.
The link between Guillain-Barré syndrome and the flu vaccination isn't clear. But researchers say concerns about the possible risk of developing Guillain-Barré syndrome after vaccination emerged after an association was noticed during the 1976-1977 "swine influenza" season, and the fact that Guillain-Barré syndrome is the most frequently reported nervous system condition reported after flu vaccination.
Flu Vaccine-Related Guillain-Barré Syndrome Cases Declining
In the study, CDC researchers examined the number of Guillain-Barré syndrome cases reported in adults who received a flu vaccine from July 1990 through June 2003.
During that time, the CDC received 500 reports of Guillain-Barré syndrome following flu vaccination.
They found the annual rates of the disorder decreased from a high of 0.17 cases per 100,000 flu vaccinations in 1993-1994 to a low of 0.04 cases per 100,000 in 2002-2003, which is a fourfold drop.
Guillain-Barré syndrome was confirmed by medical diagnosis in 82% of these cases reported to the CDC, and a preceding illness within four weeks of vaccination that may have also triggered the disorder was identified in 24% of all cases.
Researchers found there was also a longer delay between the time people received their flu shot and when symptoms of Guillain-Barré syndrome, such as weakness or a tingling sensation in the legs, emerged compared with other reported complications.
For example, symptoms emerged within 14 days of vaccination in 59% of all Guillain-Barré syndrome cases compared with 95% of all other reported complications.
The results appear in the Nov. 24 issue of The Journal of the American Medical Association.