Vaccines v placebo for preventing influenza in healthy adults at mean 87 days*
| Outcomes | Comparisons | Weighted event rates | Number of trials | RRR (95% CI) | NNT (CI) |
|---|---|---|---|---|---|
| CDI unspecified | IA v placebo | 7.2% v 20% | 1 | 65% (32 to 82) | 8 (4 to 63) |
| IP v placebo | 17% v 21% | 5 | 31% (5 to 51) | 25 (13 to 250) | |
| CDI specified | IP v placebo | 45% v 53% | 4 | 26% (1 to 45) | 13 (8 to 29) |
| SCI | LA v placebo | 0.7% v 8.5% | 2 | 79% (44 to 92) | Not significant |
| IP v placebo | 2.9% v 8.7% | 4 | 65% (44 to 79) | 18 (12 to 34) |
| RRI (CI) | NNH (CI) | ||||
|---|---|---|---|---|---|
| *CDI = clinically defined influenza; IA = inactivated aerosol vaccine; IP = inactivated parenteral vaccine; LA = live aerosol vaccine; SCI = serologically confirmed influenza. Other abbreviations defined in glossary; RRR, RRI, NNT, NNH, and CI calculated from data in article using random effects. | |||||
| Local adverse events | IP v placebo | 64% v 35% | 4 | 113% (35 to 236) | 4 (3 to 7) |