cb Kaplan 1982.

Methods	Surveillance population‐based study conducted in the USA during the 1979 to 1980 and 1980 to 1981 influenza seasons. The study tested the association between influenza vaccination and Guillain‐Barré syndrome. Reports from each case were obtained from neurologists. All case reports were included. The follow‐up period was 1 September 1979 to 31 March 1980 and 1 September 1980 to 31 March 1981.
Participants	USA (minus Maryland), adult population, 18 years or older
Interventions	Seasonal parenteral vaccine
Outcomes	Cases of Guillain‐Barré syndrome. Vaccine‐associated cases were defined as those with onset within the 8‐week period after influenza vaccination.
Notes	Vaccination rates in the population were obtained from a national immunisation 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