cb Lasky 1998.

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 databases were used to identify cases. Hospital charts were reviewed to confirm diagnosis. The follow‐up period was 1 September 1992 to 28 February 1993 and 1 September 1993 to 28 February 1994.
Participants	Approximately 21 million people, 18 years or older
Interventions	Seasonal parenteral 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. Rare events (safety) Government funded
Risk of bias
Bias	Authors' judgement	Support for judgement
PCS/RCS ‐ selection exposed cohort All outcomes	High risk	High risk
PCS/RCS ‐ selection non‐exposed cohort All outcomes	High risk	High risk
PCS/RCS ‐ comparability All outcomes	High risk	High risk
PCS/RCS ‐ assessment of outcome All outcomes	High risk	High risk
Summary assessment	High risk	High risk