Kaplan 1982.

Study characteristics
Methods	Surveillance population‐based study conducted in the USA during the 1979 to 1980 and 1980 to 1981 influenza seasons. Case report for each case was obtained from neurologists. All case reports were included. 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 trivalent 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 population were obtained from national immunisation survey.
Risk of bias
Bias	Authors' judgement	Support for judgement
Allocation concealment (selection bias)	Unclear risk	D ‐ Not used