Guillain-Barré syndrome (GBS) is a rare disorder where the body’s immune system damages nerve cells, causing muscle weakness and sometimes paralysis. While its cause is not fully understood, the syndrome often follows infection with a virus or bacteria. In the United States, an estimated 3,000 to 6,000 people develop GBS each year. Most people recover fully from GBS, but some have permanent nerve damage.
GBS is rare.
Anyone can develop GBS but people older than 50 are at greatest risk. In addition, about two-thirds of people who get GBS do so several days or weeks after they have been sick with diarrhea or a lung or sinus illness. Infection with the bacteria Campylobacter jejuni, which causes gastroenteritis (including symptoms of nausea, vomiting and diarrhea), is one of the most common risk factors for GBS. People also can develop GBS after having the flu or other infections such as cytomegalovirus and Epstein Barr virus. On very rare occasions, people develop GBS in the days or weeks after getting a vaccination.
To study whether a new vaccine might be causing GBS, CDC would compare the usual rate of GBS to the observed rate of GBS in persons getting vaccinated. This helps to determine whether a vaccine could be causing more cases.
GBS and the link to flu vaccine
In 1976, there was a small increased risk of GBS after swine flu vaccination, which was a special flu vaccine for a potential pandemic strain of flu virus. The Institute of Medicine (IOM) conducted a scientific review of this issue in 2003 and found that people who received the 1976 swine flu vaccine had an increased risk for developing GBS. The increased risk was approximately one additional case of GBS for every 100,000 people who got the swine flu vaccine. Scientists have several theories about the cause, but the exact reason for this link remains unknown.
There have been several studies of the risk of GBS after flu vaccine and CDC monitors for GBS during each flu season. The data on an association between seasonal influenza vaccine and GBS have been variable from season-to-season. When there has been an increased risk, it has consistently been in the range of 1-2 additional GBS cases per million flu vaccine doses administered.
Studies suggest that it is more likely that a person will get GBS after getting the flu than after vaccination. It is important to keep in mind that severe illness and death are associated with flu, and getting vaccinated is the best way to prevent flu infection and its complications.
CDC and FDA closely monitor the safety of all vaccines.
Tracking vaccine safety is a high priority for CDC. Several systems are in place to monitor vaccine safety. One of these systems is the Vaccine Adverse Event Reporting System (VAERS).
CDC and the U.S. Food and Drug Administration (FDA) co-manage VAERS, which serves as an early warning system to detect possible health problems that people experience following vaccinations. Anyone can report a suspected health problem after vaccination to VAERS. CDC and FDA scientists regularly review reports to detect new, unusual, or rare health events that could be linked to vaccines.
Another system is the Vaccine Safety Datalink (VSD). The VSD is a collaborative project between CDC’s Immunization Safety Office and eight integrated healthcare organizations. CDC conducts near real-time monitoring of influenza vaccine safety in the VSD each influenza season.
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