| Methods |
Randomised controlled trial, double‐blind, conducted in the USA during the 1968 to 1969 influenza season. Follow‐up lasted the whole epidemic period. Epidemic curve was traced by absenteeism in the local industries and schools and virus isolation and lasted 7 weeks. Randomisation methods were not described. One‐half of the volunteers gave serial blood and nasal wash samples. |
| Participants |
590 schoolteachers: 471 treated and 119 placebo. Age of participants was not indicated. |
| Interventions |
Polyvalent inactivated intramuscular vaccine. Schedule and dose were: 1 or 2 doses. Vaccine composition was: A2/Japan/170/62 150 CCA units, A2/Taiwan/1/64 150 CCA units, B/Massachusetts/3/66 300 CCA units. Placebo was saline for injection. Vaccine was recommended but did not match the circulating strain. |
| Outcomes |
Clinical cases and side effects. Clinical case definition was based on the presence of a temperature > 100 °F or a feverish feeling plus any 2 of the following symptoms: sore throat, muscle or joint pain, cough, stuffy or runny nose. Passive surveillance was carried out. |
| Notes |
Data concerning adverse effects were only partially reported by graph. Circulating strain was A2/Hong Kong/68. Efficacy data only 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) |
Unclear risk |
Unclear |
| 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 |
