| Study characteristics |
| Methods |
Experimental study conducted in Liverpool, UK during the 1999 to 2000 influenza season, randomised, single‐blind, placebo controlled. Data sources were self administered questionnaire and medical records. Follow‐up period was the entire winter season. |
| Participants |
729 community‐dwelling elderly without risk factors (552 treated and 177 controls, all included in the analysis), 65 to 74 years old |
| Interventions |
Parenteral influenza vaccine: A/Beijing/262/95, A/Sydney/5/97, B/Beijing/184/93. All participants also received pneumococcal vaccine. Vaccine strains matched the circulating strains. |
| Outcomes |
Clinically defined ILI (all of the following symptoms: sudden onset, fever, cough, prostration, weakness, myalgia, widespread aches), pneumonia, hospitalisation for any respiratory illness, death from all causes |
| Notes |
Vaccine contained the WHO recommended strains. The study was supposed to run for 2 influenza seasons: 99‐00 and 00‐01. After the first season, the UK's Department of Health changed the coverage policy for influenza vaccine, and recruitment to the placebo arm dwindled, affecting the validity of the trial. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Random sequence generation (selection bias) |
Low risk |
Computer random number generation |
| Allocation concealment (selection bias) |
Low risk |
Opaque envelopes were sealed and serially numbered to assign participants to intervention. |
| Blinding (performance bias and detection bias)
All outcomes |
Unclear risk |
Described as placebo controlled, but no further details provided. |
| Incomplete outcome data (attrition bias)
All outcomes |
Unclear risk |
Insufficient information available to reliably assess. |
