Influenza vaccines (inactivated parenteral vaccine [IP], live aerosol vaccine [LA], or inactivated aerosol vaccine [IA]) v placebo for preventing influenza in healthy persons 14–60 years of age at a mean follow up of 87 days*
| Outcome | Number of trials (n) | Comparison | Weighted event rates | RRR (95% CI)† | NNT (CI) |
|---|---|---|---|---|---|
| *CDI = clinically defined influenza; SCI = serologically confirmed influenza. Other abbreviations defined in glossary; weighted event rates, NNT, and CI calculated from data in article using a random effects model. | |||||
| †RRR is referred to as vaccine efficacy in the original Cochrane review. | |||||
| CDI unspecified | 8 (6566) | IP v placebo | 17% v 21% | 31% (5 to 51) | 25 (13 to ∞) |
| 2 (438) | IA v placebo | 7% v 20% | 65% (32 to 82) | 8 (4 to 50) | |
| CDI specified | 10 (4271) | IP v placebo | 36% v 44% | 22% (9 to 33) | 12 (7 to 34) |
| 2 (4591) | LA v placebo | 20% v 23% | 15% (5 to 24) | 34 (17 to 100) | |
| 2 (1069) | IA v placebo | 20% v 28% | 27% (0 to 47) | 17 (7 to ∞) | |
| SCI | 9 (2411) | IP v placebo | 2% v 8% | 67% (51 to 78) | 17 (13 to 34) |
| 2 (427) | LA v placebo | 0.5% v 8.5% | 79% (44 to 92) | 13 (6 to ∞) | |