| Methods |
Randomised controlled trial, double‐blind, conducted in the USA during the 1986 to 1987 influenza season. Follow‐up lasted the whole epidemic period. Influenza period was defined by viral surveillance. Specimens for culture and acute‐convalescent blood specimens were obtained from ill people. At spring time, volunteers were asked to record any illness that occurred during the epidemic period, and blood specimens were collected. |
| Participants |
940 healthy employees working in the Texas Medical Center in Houston, Texas, or in surrounding industrial companies: 723 treated and 217 placebo. Age of participants was 30 to 60. |
| Interventions |
Trivalent, killed, whole, intramuscularly administered vaccine. Schedule and dose were: 2 doses; 15 µg of haemagglutinin of each influenza strain. Vaccine composition was: A/Mississippi/1/85/H3N2), A/Chile/1/83 (H1N1), and B/Ann Arbor/1/86 plus A/Taiwan/1/86 (H1N1). Placebo was sterile saline for injection. Vaccine was recommended but did not match the circulating strain. |
| Outcomes |
ILI, influenza. Illnesses were classified as "any", "flu‐like" (lower respiratory or systemic illness, or both), and "febrile" (oral temperature of 37.8 °C or higher). Laboratory confirmation was based on culture and/or 4‐fold or greater rise in antibody titre occurring between postvaccination (pre‐epidemic), acute, convalescent and/or spring (postepidemic) sera. Surveillance was passive. |
| Notes |
Influenza‐like illness and influenza cases were detected in 3 groups: first vaccinated, multivaccinated, and placebo. Febrile illnesses were included in the analysis; the first 2 groups' cases were combined. Circulating strain was A/Taiwan/1/86. Effectiveness data only were extracted. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Random sequence generation (selection bias) |
Low risk |
Volunteers were randomly allocated to receive vaccine or placebo using a table of random numbers according to prior vaccination experience. |
| Allocation concealment (selection bias) |
Unclear risk |
Insufficent information available to judge |
| Blinding (performance bias and detection bias)
All outcomes |
Unclear risk |
Described as double‐blind, but no further details available. |
| Incomplete outcome data (attrition bias)
All outcomes |
Unclear risk |
No description |
| Summary assessment |
Unclear risk |
No description |
