Why did some people develop Guillain-Barre syndrome (GBS) after they received the 1976 swine flu vaccine?

The Institute of Medicine (IOM) conducted a thorough scientific review in 2003 and concluded that people who received the 1976 swine influenza vaccine had a slight increased risk for developing GBS. Scientists have multiple theories on why this increased risk may have occurred, but the exact reason for this association remains unknown.

For more information about Guillain-Barré Syndrome see:

• National Institute of Neurological Disorders and Stroke Information Page
• Fact Sheet: Guillain-Barré Syndrome 

Last Updated: 09/14/2009

• What happened in 1976 with Guillain-Barre syndrome (GBS) and the swine flu vaccine?
• What causes Guillain-Barre syndrome (GBS)?
• How common is Guillain-Barre syndrome (GBS), and how common is it after people are vaccinated for seasonal flu?

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    • Guillain-Barre Syndrome (GBS)