Risk of Guillain-Barré Syndrome from Influenza Vaccination
The risk of developing Guillain-Barré syndrome (GBS) after receiving the flu shot is extremely low—approximately 1 additional case per 1 million people vaccinated—and this small risk is substantially outweighed by the benefits of preventing severe influenza illness, hospitalization, and death. 1
Quantifying the Risk
The evidence consistently demonstrates minimal GBS risk associated with modern influenza vaccines:
- The estimated excess risk is approximately 1-1.6 additional cases of GBS per million vaccinations, with cases typically peaking 2 weeks after vaccination 1, 2
- A 2013 Canadian study found the attributable risk was 1.03 GBS admissions per million vaccinations, compared to 17.2 GBS admissions per million influenza-coded healthcare encounters (meaning influenza infection itself carries a 15-fold higher GBS risk than vaccination) 3
- The relative incidence of GBS within 6 weeks of vaccination was 1.52 (95% CI 1.17-1.99) compared to control periods, while the relative incidence after actual influenza illness was 15.81 (95% CI 10.28-24.32) 3
Context and Perspective
The absolute risk is extraordinarily small and must be weighed against the substantial morbidity and mortality prevented by vaccination:
- Only 0.4% of all GBS cases in Denmark were attributable to recent influenza vaccination in a 15-year nationwide study 4
- The case-fatality ratio for GBS is 6% and increases with age, but this mortality rate does not differ between vaccinated and unvaccinated persons who develop GBS 1
- Influenza-associated hospitalization rates range from 200-300 per million for healthy adults to 2,000-10,000 per million for persons aged ≥65 years during epidemics 1
- Influenza-associated death rates range from 300 to >1,500 per million persons aged ≥65 years during epidemics 1
Important Caveats
The 1976 swine influenza vaccine was an exception, with a substantially higher GBS rate of approximately 10 cases per million vaccinated 1. This has not been observed with subsequent seasonal or pandemic influenza vaccines 1.
Special Considerations for Patients with Prior GBS
The approach differs based on risk stratification:
- For persons NOT at high risk for severe influenza complications who developed GBS within 6 weeks of a previous influenza vaccination: generally should not receive subsequent influenza vaccines; consider antiviral chemoprophylaxis as an alternative 1
- For persons at HIGH risk for severe influenza complications with a history of GBS: the established benefits of influenza vaccination likely outweigh risks, and yearly vaccination may be justified 1
- A Kaiser Permanente study following 107 persons with prior GBS found zero cases of recurrent GBS after influenza vaccination over an 11-year period, including 2 individuals who initially developed GBS within 6 weeks of vaccination 5
Clinical Bottom Line
The odds of getting GBS from the flu shot are approximately 1 in 1 million, while the odds of getting GBS from influenza infection itself are approximately 17 in 1 million—making the infection 15-17 times more likely to cause GBS than the vaccine. 3 This risk-benefit calculation strongly favors vaccination for the vast majority of individuals.