What causes GBS?
Scientists do not fully understand what causes GBS, but it is believed that stimulation of the body’s immune system may play a role in its development. Here’s what scientists know for sure: About two-thirds of people who develop GBS symptoms do so several days or weeks after they have been sick with a diarrhea or respiratory illness. Infection with the bacterium Campylobacter jejuni is one of the most common risk factors for GBS. People can also develop GBS after having the flu or other infections (such as cytomegalovirus and Epstein Barr virus). On very rare occasions, they may develop GBS in the days or weeks following receiving a vaccination.<snip>
Do vaccines cause GBS?
It is not fully understood why some people develop GBS, but it is believed that the nerve cells are damaged by a person’s own immune system. Many types of infections, and in very rare cases vaccines, may activate the immune system to cause damage to the nerve cells.
How common is GBS, and how common is it after people are vaccinated for seasonal influenza?
GBS is rare. Each year, about 3,000 to 6,000 people in the United States develop GBS whether or not they received a vaccination – that’s 1 to 2 people out of every 100,000 people. This is referred to as the background rate.
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In 1976, there was a small risk of GBS following influenza (swine flu) vaccination (approximately 1 additional case per 100,000 people who received the swine flu vaccine). That number of GBS cases was slightly higher than the background rate for GBS. Since then, numerous studies have been done to evaluate if other flu vaccines were associated with GBS. In most studies, no association was found, but two studies suggested that approximately 1 additional person out of 1 million vaccinated people may be at risk for GBS associated with the seasonal influenza vaccine. It is important to keep in mind that severe illness and possible death can be associated with influenza, and vaccination is the best way to prevent influenza infection and its complications.