| Methods |
Single‐blind randomised controlled trial conducted in the USA during the 1974 to 1975 influenza season. Follow‐up lasted from winter to spring. A "two‐month" epidemic period was described by the authors with no reference to a definition and lasted 6 weeks. Study participants were randomly assigned into 3 subgroups to receive either 2 doses of the vaccine (n = 47), 1 dose of vaccine and 1 dose of placebo (n = 48), or 2 doses of placebo (n = 48) at 14 days apart. 6‐month sera were collected on all study participants. |
| Participants |
34 healthy university students: 26 treated and 8 placebo. Age of participants was 18 to 45. |
| Interventions |
Subvirion monovalent parenteral vaccine. Schedule and dose were: single dose; 90 µg rHA0. Vaccine composition was: the recombinant HA vaccine contained HA0 glycoprotein from the influenza A/Beijing/32/92 (H3N2) virus. Placebo was saline for injection. Vaccine was not recommended but matched circulating strain. |
| Outcomes |
Clinical and laboratory‐confirmed cases. An "influenza‐like illness" was defined as the presence of any respiratory symptom(s) for >= 2 days, accompanied by fever or systemic symptoms of myalgia or chills. Laboratory evidence of influenza A (H3N2) virus infection was defined as either or both of the isolation of virus from nasopharyngeal secretion and a >= 4‐fold increase in serum HI antibody titre between the 3‐week postvaccination (preseason) specimen and the corresponding postseason specimen collected in the following spring. |
| Notes |
Safety data were not included; effectiveness data were extracted. |
| 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 |
