Table 3.
Incidence of blood culture-confirmed typhoid fever and protective effectiveness of Vi-TT by age group*
|
Events/person-years† |
Incidence, per 100 000 person-years |
Protective effectiveness | p value | p value for interaction | |||
|---|---|---|---|---|---|---|---|
| SA 14-14-2 group | Vi-TT group | SA 14-14-2 group | Vi-TT group | ||||
| Total vaccine protection | |||||||
| 9 months to <2 years | 23/2804 | 4/2800 | 820 (520–1231) | 143 (39–366) | 81% (39 to 94) | 0·0052 | 0·49 |
| 2 to 4 years | 62/6413 | 12/6173 | 967 (741–1239) | 194 (100–340) | 80% (62 to 89) | <0·0001 | .. |
| 5 to <16 years† | 107/21 037 | 13/21 375 | 509 (417–615) | 61 (32–104) | 88% (78 to 93) | <0·0001 | .. |
| Overall vaccine protection | |||||||
| <2 years | 35/7779 | 13/7861 | 450 (313–626) | 165 (88–283) | 63% (20 to 83) | 0·011 | 0·056 |
| 2 to 4 years | 86/9295 | 34/9041 | 925 (740–1143) | 376 (260–526) | 59% (40 to 73) | <0·0001 | .. |
| 5 to <16 years | 141/32 316 | 50/32 462 | 436 (367–515) | 154 (114–203) | 65% (50 to 75) | <0·0001 | .. |
| ≥16 years† | 69/106 069 | 47/105 085 | 65 (51–82) | 45 (33–59) | 33% (−2 to 55) | 0·061 | .. |
| Indirect vaccine protection | |||||||
| <2 years | 12/4846 | 8/4913 | 248 (128–433) | 163 (70–321) | 32% (−127 to 80) | 0·53 | 0·38 |
| 2 to 4 years | 24/2884 | 23/2880 | 832 (533–1238) | 799 (506–1198) | 6% (−78 to 51) | 0·84 | .. |
| 5 to <16 years | 34/11 415 | 37/11 227 | 298 (206–416) | 330 (232–454) | −13% (80 to 29) | 0·60 | .. |
| ≥16 years† | 69/106 061 | 47/105 081 | 65 (51–82) | 45 (33–59) | 33% (−2 to 55) | 0·060 | .. |
Data are incidence rate/person-years, n (95% CI), or % (95% CI). SA 14-14-2=Japanese encephalitis vaccine. Vi-TT=Vi-tetanus toxoid conjugate vaccine.
Age at vaccination for the subgroup analyses of total vaccine protection, and age at date of residence for that of overall and indirect vaccine protection analyses; protective effectiveness, p values and CIs were adjusted for the stratifying variables for randomisation, including geographical ward, distance to study clinics, number of eligible children at baseline, and other baseline covariates prespecified in the statistical analysis plan, including age, sex, toilet type in the house, drinking water source, treatment of drinking water, handwashing before meals, and handwashing after defecation.
11 vaccinees were ≥16 years at vaccination and were included in the total vaccination analysis of the 5 to <16 years age group, resulting in a 12 person-years difference between overall and indirect vaccine protection analysis of the ≥16 years age group.