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Efficacy of typhoid conjugate vaccine in Nepal: final results of a phase 3, randomised, controlled trial
Mila Shakya1, Merryn Voysey2, Katherine Theiss-Nyland2
1Oxford University Clinical Research Unit, Patan Academy of Health Sciences, Lalitpur, Nepal.
Insights
The typhoid conjugate vaccine (TCV) demonstrated 79% efficacy in preventing typhoid fever in Nepali children over two years. This vaccination is crucial for controlling enteric fever in low-resource settings.
Area of Science:
- Public Health
- Vaccinology
- Infectious Diseases
Background:
- Typhoid fever poses a significant public health challenge, particularly in resource-limited regions.
- Vaccination strategies, including the typhoid conjugate vaccine (TCV), are essential for disease control and reducing transmission.
- Previous interim analyses indicated TCV's potential efficacy in Nepali children.
Purpose of the Study:
- To report the final 2-year efficacy results of the typhoid conjugate vaccine (TCV) in Nepali children.
- To evaluate the sustained protective effect of TCV against blood culture-confirmed typhoid fever.
- To provide evidence supporting global recommendations for enteric fever control.
Main Methods:
- A participant-masked and observer-masked individually randomized controlled trial was conducted in Lalitpur, Nepal.
- 20,019 children aged 9 months to 16 years were randomized (1:1) to receive either TCV or a meningococcal group A conjugate vaccine (MenA).
- Follow-up extended to April 9, 2020, with typhoid fever cases identified through passive and active surveillance.
Main Results:
- The final analysis included 75 cases of blood culture-confirmed typhoid fever (13 in TCV group, 62 in MenA group).
- Typhoid conjugate vaccine (TCV) demonstrated a 2-year protective efficacy of 79.0% against blood culture-confirmed typhoid fever.
- Incidence rates were significantly lower in the TCV group (72 per 100,000 person-years) compared to the MenA group (342 per 100,000 person-years).
Conclusions:
- The final results align with interim findings, confirming TCV's efficacy in preventing typhoid fever.
- No evidence of waning protection was observed over the 2-year follow-up period.
- These findings strongly support the World Health Organization's recommendations for enteric fever control through vaccination.
Background:
Typhoid fever is a major public health problem in low-resource settings. Vaccination can help curb the disease and might reduce transmission. We have previously reported an interim analysis of the efficacy of typhoid conjugate vaccine (TCV) in Nepali children. Here we report the final results after 2 years of follow-up.
Methods:
We did a participant-masked and observer-masked individually randomised trial in Lalitpur, Nepal, in which 20 019 children aged 9 months to younger than 16 years were randomly assigned in a 1:1 ratio to receive a single dose of TCV (Typbar TCV, Bharat Biotech International, India) or capsular group A meningococcal conjugate vaccine (MenA). Participants were followed up until April 9, 2020. The primary outcome was blood culture-confirmed typhoid fever. Cases were captured via passive surveillance and active telephone surveillance followed by medical record review. The trial is registered at ISRCTN registry, ISRCTN43385161 and is ongoing.
Findings:
From Nov 20, 2017, to April 9, 2018, of 20 119 children screened, 20 019 participants were randomly assigned to receive TCV or MenA vaccine. There were 75 cases of blood culture-confirmed typhoid fever included in the analysis (13 in the TCV group and 62 in the MenA group) over the 2-year period. The protective efficacy of TCV against blood culture-confirmed typhoid fever at 2 years was 79·0% (95% CI 61·9-88·5; p<0·0001). The incidence of typhoid fever was 72 (95% CI 38-123) cases per 100 000 person-years in the TCV group and 342 (95% CI 262-438) cases per 100 000 person-years in the MenA group. Adverse events occurring within the first 7 days post-vaccination were reported previously.
Interpretation:
The final results of this randomised, controlled trial are in keeping with the results of our published interim analysis. There is no evidence of waning protection over a 2-year period. These findings add further support for the WHO recommendations on control of enteric fever.
Funding:
Bill & Melinda Gates Foundation.
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