Table 3. Vaccine Efficacy Measurements, According to Analysis and Study Group*.
| Outcome | Intention-to-Treat Analysis | Per-Protocol Analysis | ||||
|---|---|---|---|---|---|---|
| Vaccine (N = 43) |
Placebo (N = 41) |
Relative Reduction | Vaccine (N = 38) |
Placebo (N = 39) |
Relative Reduction | |
| no. (%) | % (95% CI) | no. (%) | % (95% CI) | |||
| Norwalk virus infection and illness | 17 (40) | 29 (71) | 44 (15.0 to 63.2) | 14 (37) | 27 (69) | 47 (15 to 67) |
| Norwalk virus infection | ||||||
| Positive RT-PCR assay | 28 (65) | 33 (80) | 19 (−6 to 38) | 23 (61) | 32 (82) | 26 (1 to 45) |
| Positive for antigen | 25 (58) | 24 (59) | 1 (−43 to 31) | 20 (53) | 23 (59) | 11 (−33 to 40) |
| Seroconversion | 27 (63) | 34 (83) | 24 (1 to 42) | 23 (61) | 32 (82) | 26 (1 to 45) |
| Positive on any assay | 28 (65) | 34 (83) | 22 (−2 to 39) | 23 (61) | 32 (82) | 26 (1 to 45) |
| Vaccine (N = 43) |
Placebo (N = 41) |
P Value† | Vaccine (N = 38) |
Placebo (N = 39) |
P Value† | |
| Vesikari score for disease severity‡ | ||||||
| All participants | 3.8±2.8 | 5.5±2.6 | 0.008 | 3.6±2.9 | 5.5±2.7 | 0.009 |
| Norwalk virus infection | 5.0±2.4 | 6.1±2.4 | 0.07 | 5.0±2.6 | 6.1±2.4 | 0.14 |
| Norwalk virus infection and illness | 6.2±1.9 | 6.7±2.1 | 0.39 | 6.4±2.1 | 6.7±2.2 | 0.72 |
| Duration of Norwalk virus illness — hr | ||||||
| Norwalk virus infection, all | 0.28 | 0.47 | ||||
| Median | 18.4 | 30.2 | 14.5 | 29.4 | ||
| Range | 0.0 to 85.5 | 0.0 to 108.0 | 0.0 to 85.5 | 0.0 to 108.0 | ||
| Norwalk virus infection and illness | 0.44 | 0.45 | ||||
| Median | 45.4 | 36.2 | 44.0 | 34.7 | ||
| Range | 8.6 to 85.5 | 5.2 to 108.0 | 8.6 to 85.5 | 5.2 to 108.0 | ||
| Time to illness onset — hr | 37.1±7.0 | 32.8±9.0 | 0.02 | 35.9±7.1 | 33.8±6.7 | 0.12 |
*
Plus–minus values are means ±SD. Illness was defined as viral gastroenteritis. RT-PCR denotes reverse transcriptase–polymerase chain reaction.
†
P values were calculated with the use of the Wilcoxon test, except for comparisons of the time to onset of illness, for which the log-rank test was used.
‡
The severity of norovirus disease was assessed on the basis of the modified Vesikari score, with possible scores ranging from 0 to 17 and higher scores indicating more severe disease.