| 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 |
243 volunteer students and staff members: 194 treated and 49 placebo. Age of participants was not indicated. |
| Interventions |
Bivalent AB aerosol vaccine. Vaccine composition was: A2/Japan/170/62 150 CCA units, A2/Taiwan/1/64 150 CCA units, and B/Massachusetts/3/66 200 CCA units. Placebo was saline for injection. Vaccine was recommended but did not match the 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 |
