| Study characteristics |
| Methods |
Surveillance population‐based study conducted in the USA (4 states: Illinois, Maryland, North Carolina, Washington) during the 1992 to 1993 and 1993 to 1994 influenza seasons. Discharge diagnoses database was used to identify cases. Hospital charts were reviewed to confirm diagnosis. Follow‐up period was 1 September 1992 to 28 February 1993 and 1 September 1993 to 28 February 1994. |
| Participants |
About 21 million people, 18 years or older |
| Interventions |
Seasonal trivalent vaccine |
| Outcomes |
Cases of Guillain‐Barré syndrome. Vaccine‐associated cases were defined a priori as those with onset within the 6‐week period after influenza vaccination. |
| Notes |
Results were stratified by age and adjusted by season and sex. Vaccination rates in population were estimated from a random‐digit dialling telephone survey. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Allocation concealment (selection bias) |
Unclear risk |
D ‐ Not used |
