Schonberger 1979.

Study characteristics
Methods	Surveillance population‐based study conducted in the USA during the 1976 to 1977 influenza season. Neurologists were directly contacted; physician and hospital records were reviewed. Suspected cases reported to the Centers for Disease Control and Prevention directly by patients or medical personnel were included only if accepted by a state health department. Follow‐up period was 1 October 1976 to 31 January 1977.
Participants	USA population
Interventions	Monovalent A/New Jersey/76 or bivalent A/New Jersey/76 and A/Victoria/75 parenteral vaccine
Outcomes	Cases of Guillain‐Barré syndrome
Notes	Results were stratified by age group and vaccine type. 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