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Safety and immunogenicity of Vi-DT conjugate vaccine among 6-23-month-old children: Phase II, randomized,
Maria Rosario Capeding1, Arijit Sil2, Birkneh Tilahun Tadesse2
1Research Institute for Tropical Medicine, Manila, The Philippines.
Insights
The Vi-DT typhoid conjugate vaccine is safe and effective in children aged 6-23 months, demonstrating high immunogenicity with both single and two-dose schedules. This offers a promising new tool to reduce typhoid mortality in young children.
Area of Science:
- Vaccinology
- Pediatric Infectious Diseases
- Public Health
Background:
- Typhoid fever causes substantial mortality in young children, particularly in resource-limited regions.
- A limited number of WHO-prequalified typhoid conjugate vaccines are available for this age group.
- There is a critical need for additional typhoid conjugate vaccines for infants and toddlers.
Purpose of the Study:
- To evaluate the safety, immunogenicity, and optimal dose-scheduling of the Vi-DT typhoid conjugate vaccine.
- To assess the vaccine's efficacy in children aged 6-23 months.
Main Methods:
- A single-center, observer-blind, phase II randomized trial was conducted.
- Participants (N=285) were assigned to receive one or two doses of Vi-DT or a comparator vaccine.
- Anti-Vi IgG titers and geometric mean titers (GMT) were measured at multiple time points.
Main Results:
- The Vi-DT vaccine demonstrated a satisfactory safety profile, with no vaccine-related serious adverse events.
- Seroconversion rates were high (100% after one dose, 98.2% after two doses) in Vi-DT recipients compared to the comparator group (7.0% and 21.8%, respectively).
- Significantly higher anti-Vi IgG GMTs were observed in Vi-DT recipients post-vaccination.
Conclusions:
- Both single and two doses of the Vi-DT vaccine are safe and well-tolerated in infants and toddlers.
- The Vi-DT vaccine is highly immunogenic in this pediatric population.
- Vi-DT represents a promising new typhoid conjugate vaccine for preventing childhood typhoid.
Background:
Typhoid causes significant mortality among young children in resource-limited settings. Conjugate typhoid vaccines could significantly reduce typhoid-related child deaths, but only one WHO-prequalified typhoid conjugate vaccine exists for young children. To address this gap, we investigated the safety, immunogenicity and dose-scheduling of Vi-DT typhoid conjugate vaccine among children aged 6-23 months.
Methods:
In this single center, observer blind, phase II trial, participants were randomly assigned (2:2:1) to receive one or two doses of Vi-DT or comparator vaccine. Anti-Vi IgG titer and geometric mean titers (GMT) were determined at 0, 4, 24 and 28 weeks. Data were analyzed using per-protocol and immunogenicity (a subset of intention-to-treat analysis) sets. The trial is registered with ClinicalTrials.gov (NCT03527355).
Findings:
Between April and July 2018, 285 children were randomized; 114 received one or two doses of Vi-DT while 57 received comparator. 277 completed the study follow-up per protocol; 112 and 110 from single- and two-dose Vi-DT schedules, respectively and 55 from the placebo group were included in the per protocol analysis. Safety profile is satisfactory. Thirteen serious adverse events were reported during the 28-week follow-up, none of which were related to Vi-DT. The seroconversion rate four weeks after the first dose was 100% (95% CI 98·3-100) in Vi-DT recipients and 7·0% (95% CI 2·8-16·7) in comparator recipients (p<0·0001). Similarly, the seroconversion rate 4 weeks after the second dose was 98·2% (95% CI 93· 6-99·5) and 21·8% (95% CI 13·0-34·4) among Vi-DT and comparator groups, respectively (p<0·0001). Anti-Vi IgG GMT was significantly higher in Vi-DT than in control group at all post-vaccination visits (p<0·0001).
Interpretation:
Both single and two doses of Vi-DT vaccine are safe, well tolerated, and immunogenic for infants and toddlers in a moderately endemic setting.
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