Table 2. Overall and indirect vaccine effectiveness against cholera using ring vaccination strategy.
| Duration of Follow-Up | High Vaccine Coverage Cohorts* (Coverage ≥ 30%) | Low Vaccine Coverage Cohorts* (Coverage ≤ 12%) | VE (95% CI; p-Value) | |||
|---|---|---|---|---|---|---|
| Index Cases/Population † | Number of Cases ‡ (IR/1,000) | Index Cases/Population † | Number of Cases ‡ (IR/1,000) | Crude | Adjusted £ | |
| Overall VE | ||||||
| 2 y | 55/22,344 | 2 (0.09) | 51/21,254 | 22 (1.04) | 91% (63 to 98; <0.001) | 91% (62 to 98; 0.0011) |
| 3 y | 116/46,059 | 7 (0.15) | 95/40,380 | 29 (0.72) | 79% (52 to 91; <0.001) | 75% (44 to 89; <0.001) |
| 4 y | 156/64,295 | 17 (0.26) | 136/62,287 | 44 (0.71) | 63% (35 to 79; <0.001) | 62% (32 to 79; 0.0012) |
| 5 y | 182/72,978 | 18 (0.25) | 151/68,790 | 44 (0.64) | 62% (33 to 78; <0.001) | 62% (31 to 79; <0.001) |
| Indirect VE | ||||||
| 2 y | 55/12,998 | 1 (0.08) | 51/20,624 | 22 (1.07) | 93% (47 to 99; 0.0101) | 93% (44 to 99; 0.0113) |
| 3 y | 116/27,452 | 5 (0.18) | 95/38,615 | 29 (0.75) | 76% (37 to 91; 0.0034) | 72% (27 to 89; 0.0088) |
| 4 y | 156/38,760 | 13 (0.34) | 136/59,207 | 44 (0.74) | 55% (16 to 76; 0.0117) | 52% (10 to 75; 0.0233) |
| 5 y | 182/43,900 | 14 (0.32) | 151/65,299 | 44 (0.67) | 53% (14 to 74; 0.0147) | 51% (8 to 74; 0.0257) |
*The vaccine coverage of individuals living within 25 m of index cases was calculated as the number of two-dose vaccine recipients divided by all population within 25 m.
†Number of index cases over cumulative total population within 25 m of the index cases.
‡Cumulative total cholera cases within 25 m of the index cases (excluding index cases) and within 8–28 d of onset of index cases.
£Adjusted for age for the 2-y analysis, for age and sex for the 3-y analysis, and for age, sex, and distance from household to nearest water body for the 4-y and 5-y analyses.
IR, incidence rate; VE, vaccine effectiveness.