cb Shonberger 1979.

Methods	Surveillance, population‐based study conducted in the USA during the 1976 to 1977 influenza season. The study tested the association between influenza vaccination and Guillain‐Barré syndrome. Neurologists were directly contacted; physician and hospital records were reviewed. Suspected cases were reported to the CDC directly by patients or medical personnel and 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 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	Unclear risk	High risk
PCS/RCS ‐ selection non‐exposed cohort All outcomes	Unclear risk	High risk
PCS/RCS ‐ comparability All outcomes	Unclear risk	High risk
PCS/RCS ‐ assessment of outcome All outcomes	Unclear risk	High risk
Summary assessment	Unclear risk	High risk