Fig 1.
During the screening process, participant exclusions were made either during initial telephone screening or at/after the study centre screening visit. ‘Other’ reasons for exclusions were: contact with young children (3), contact with vulnerable individuals (9), food-related occupation (5), previously resident in typhoid-endemic area for >6 months (15), unable to contact (6) & unknown (8).
Table 1.
Participant characteristics by enrolled vaccine group.
Table 2.
Summary of vaccine efficacy endpoints and severity measures reached during the 14-day challenge period.
Fig 2.
Cumulative incidence of typhoid infection after S. Typhi challenge at Time = 0.
Time to infection, measured from challenge agent ingestion to development of first fever ≥38°C or first positive blood culture sampling. Non-diagnosed participants censored at 348 hours (dashed line). P value from log-rank test comparing all three groups.
Fig 3.
Cumulative incidence of bacteraemia or fever after S. Typhi challenge at Time = 0.
(A) Time to bacteraemia, measured from challenge agent ingestion to time of first positive blood culture sampling. Non-bacteraemic participants censored at time of diagnosis or at 348 hours (dashed line). P value from log-rank test comparing all three groups and comparing M01ZH09 and Ty21a to placebo, respectively. (B) Time to fever, measured from challenge agent ingestion to first recording of fever (oral temperature ≥38°C). Afebrile participants censored at time of diagnosis or at 336 hours (dashed line). P value from log-rank test comparing all three groups.
Fig 4.
Changes in physiological signs in those participants developing typhoid by time after diagnosis according to vaccine group allocation.
(A) Temperature, (B) Heart rate and (C) Systolic blood pressure. Mean change from baseline and 95% confidence interval. Dashed black vertical line marks point of typhoid diagnosis; grey horizontal bar indicates all participant mean (95% CI) values pre-vaccination.
Fig 5.
Proportion of participants reporting each solicited symptom during 14 days after challenge according to vaccine group allocation.
(A) Placebo, (B) M01ZH09, and (C) Ty21a vaccine recipient groups. Maximum severity score per participant for each symptom was used and graded according to criteria detailed in the study protocol: fever thresholds are Grade 1: 38.0–38.4°C; Grade 2: 38.5–38.9°C; Grade 3: 39.0–40.0°C; Grade 4: >40.0°C.
Fig 6.
Group mean changes (95% confidence intervals) in haematological blood parameters compared to pre-challenge measurements according to vaccine allocation and challenge outcome.
(A) Haemoglobin, (B) platelets, (C) total white cell count, (D) neutrophils, (E) lymphocytes, and (F) eosinophils. TD, typhoid diagnosis; nTD, non-typhoid diagnosis.
Fig 7.
Group mean changes (95% confidence intervals) in biochemistry blood parameters compared to individual baseline measurements according to vaccine allocation and challenge outcome.
(A) Sodium, (B) potassium, (C) urea, (D) creatinine, (E) Albumin, (F) amylase, (G) alkaline phosphatase, (H) alanine aminotransferase, (I) bilirubin, and (J) C-reactive protein. TD, typhoid diagnosis; nTD, non-typhoid diagnosis.
Table 3.
Summary of microbiological results obtained over the entire study period (including stool clearance samples).
Fig 8.
Blood quantification of Salmonella Typhi bacteria present at point of typhoid diagnosis by vaccine group.
10mL peripheral blood was collected at typhoid diagnosis (prior to antibiotic treatment) into an Isolator 10 tube (Wampole Laboratories). Lysis centrifugation was performed (30min x 3000G without brake) after which the deposit was plated to XLD and incubated aerobically at 37°C for 24 hours. After incubation, colony counts and slide agglutination tests were performed. P values calculated using Mann Whitney U test. Median [IQR] bacterial loads in CFU/mL were: M01ZH09 (n = 14): 0.13 [0.05–0.80]; Placebo (n = 15): 1.30 [0.30–5.40]; Ty21a (n = 12): 0.05 [0.05–0.99]. Lower limit of detection, 0.1 CFU/mL; zero values were substituted with LOD/2, i.e. 0.05 CFU/mL.
Table 4.
Summary of stool shedding by participants between Day 0 (including pre-challenge) until completion of challenge, according to vaccine group allocation, challenge outcome and phase of shedding.
Fig 9.
Proportion of participants reporting each solicited symptom during the 7-days after receipt of (first) vaccine dose.
(A) Placebo, (B) M01ZH09, and (C) Ty21a vaccine recipient groups. Maximum severity score per participant for each symptom was used; grade 1: symptom reported but no interference with daily activity; grade 2: some interference with normal daily activities; grade 3: significant symptoms preventing normal daily activity; grade 4: potentially life-threatening (see S1 Protocol).
Fig 10.
Immunoglobulin G ASC and antibody responses to S. Typhi LPS and flagellin before (Day -28) and after vaccination (either Day -21 or Day 0 for ASC and ELISA assays, respectively).
(A) LPS and (B) flagellin specific IgG antibody secreting cell responses, respectively, measured pre-vaccination (Day -28) and 7 days later (Day -21). (C) Anti-LPS and (D) anti-flagellin antibody titres, respectively, measured pre-vaccination (Day -28) and 28 days later (Day 0, i.e. prior to S. Typhi challenge). Data are grouped according to vaccine allocation.
Table 5.
Analysis of covariance comparisons for increase in ASC titres against LPS, flagellin (H) and Vi between prevaccination (Day -28) and Day -21, between each active vaccine group (1. M01ZH09 and 2. Ty21a) and placebo.
Analyses were performed with the dependent variable log(change from baseline) with adjustment for log(pre-vaccination) values. GMR, geometric mean ratio compared to placebo.
Table 6.
Analysis of covariance comparisons for increase in antibody titres against LPS, flagellin (H) and Vi between pre-vaccination (Day -28) and Day 0 (prior to challenge), between each active vaccine group (1. M01ZH09 and 2. Ty21a) and placebo.
Analysis were performed with the dependent variable log(change from baseline) with adjustment for log(pre-vaccination) values. GMR, geometric mean ratio compared to placebo.
Fig 11.
Pre-vaccination (Day -28) and pre-challenge (Day 0) IgG antibody titres according to outcome after challenge.
(A) Anti-LPS IgG, (B) anti-H IgG, and (C) anti-Vi IgG. Clear circles, non-typhoid diagnosed participants; black circles, typhoid diagnosed participants. Difference between Day -28 and Day 0 anti-LPS and anti-H antibodies analysed by ANCOVA adjusted for vaccine group and baseline titre; P values for anti-Vi antibody calculated by Wilcoxon Rank Sum. Lower limit-of Vi-antibody detection, 7.4EU/mL.
Table 7.
Hazard Ratios (each active vaccine group vs. placebo) and 95% confidence intervals from proportional hazards models adjusting for baseline anti-Vi IgG antibody titres.