aa Waldman 1972b.

Methods	Randomised controlled trial, double‐blind, conducted in the USA during the 1968 to 1969 influenza season. Follow‐up lasted the whole epidemic period. The epidemic curve was traced by absenteeism in the local industries and schools and virus isolation and lasted 7 weeks. Identical‐looking, coded vials were used to dispense material. Sampling virological and serological survey of ill people was performed. 2 doses were administered, but as the outbreak occurred mostly between them, only the effectiveness of the first dose was assessed.
Participants	239 volunteer students and staff members: 190 treated and 49 placebo. Age of participants was not indicated.
Interventions	Monovalent A subcutaneous vaccine. Schedule and dose were: 200 CCA units. Vaccine composition was: A2/Aichi/1/69. Placebo was saline for injection. Vaccine was recommended and matched circulating strain.
Outcomes	Clinical cases and adverse effects. Clinical cases were defined as febrile respiratory illness with oral temperature higher then 99.5 °F. Local adverse effects were defined as pain and/or tenderness and redness and/or swelling. Systemic adverse effects were defined as general (fever, muscle pain, nausea or vomiting, diarrhoea, and malaise) or respiratory (runny and/or stuffy nose, sore throat, cough, shortness of breath). Passive surveillance was carried out.
Notes	Illness during the first 1 or 2 weeks after vaccination was not excluded, but the authors stated that this fact did not affect the results. Circulating strain was A2/Aichi/2/68. Efficacy and safety data were extracted. Government funded.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Unclear
Allocation concealment (selection bias)	Low risk	Adequate
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Unclear
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Unclear
Summary assessment	Unclear risk	Unclear