Vaccine v placebo for laboratory confirmed influenza illness‡
| Year | Vaccine | Placebo | RRR (95% CI) | NNT (CI) |
|---|---|---|---|---|
| ‡Abbreviations defined in glossary; RRR, CI, and NNT calculated from data in article. | ||||
| 1997–8 | 2.2% | 4.4% | 50% (−77 to 86) | Not significant |
| 1998–9 | 1.4% | 10.2% | 86% (47 to 96) | 12 (7 to 27) |