Adjusted vaccine effectiveness in stratified analyses or according to influenza virus characteristics
| Stratifying variable(s) | Level | V/E (95% CI) | p Value for difference between strata |
| Year | 2005/06 | 67% (41 to 82) | 0.15 |
| 2006/07 | 55% (26 to 73) | ||
| 2007/08 | 67% (41 to 82) | ||
| Period | Nov–Jan | 67% (47 to 80) | 0.51 |
| Feb–Apr | 61% (42 to 74) | ||
| Age | <65 | 70% (57 to 78) | 0.27 |
| ≥65 | 46% (−17 to 75) | ||
| Interval- illness onset to swab sample | ≤4 days | 65% (48 to 76) | 0.78 |
| >4 days | 66% (41 to 80) | ||
| Viral load | CT <30 | 59% (38 to 72) | 0.81 |
| CT ≥30 | 70% (53 to 80) | ||
| Flu type | A | 65% (50 to 75) | 0.96 |
| B | 62% (33 to 78) | ||
| Year and flu type | 2005/06 A | 66% (21 to 85) | 0.53 |
| 2005/06 B | 67% (31 to 85) | ||
| 2006/07 A | 54% (25 to 72) | ||
| 2006/07 B | - | ||
| 2007/08 A | 64%(30 to 84) | ||
| 2007/08 B | 70% (24 to 88) |