aa Hammond 1978.

Methods	Controlled clinical trial, double‐blinded conducted in Australia during the 1976 influenza season. Follow‐up lasted the whole epidemic period. Epidemic influenza was defined by virus isolation and serology tests and lasted from middle of April to middle of August 1976 (17 weeks). Coded, identical‐looking vials were sequentially administered to enrolled participants. A throat swab was collected from ill people. Serological confirmation was performed on all participants.
Participants	225 medical students or staff members: 116 treated and 109 placebo. Age of participants was not indicated.
Interventions	Trivalent parenteral subunit vaccine. Schedule and dose were: single dose; vaccine composition was: 250 IU of A/Victoria/3/75, 250 IU of A/Scotland/840/74, and 300 IU of B/Hong Kong/8/73. Placebo was diphtheria and tetanus toxoids. Vaccine was recommended and matched circulating strain.
Outcomes	Influenza‐like illness, influenza. Clinical illnesses were not defined. Influenza was defined as respiratory illness that was associated with the isolation of influenza virus, a 4‐fold or greater rise in antibody titre occurring between postvaccination and postepidemic sera, or both. Surveillance was active.
Notes	Clinical illness was not defined, and data were included in the analysis as "clinical cases without clear definition". Circulating strain was A/Vic/3/75‐like. Efficacy data only were extracted. Government funded
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	Alternate
Allocation concealment (selection bias)	High risk	No description
Blinding (performance bias and detection bias) All outcomes	Unclear risk	No description
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	No description
Summary assessment	High risk	No description