Typhoid conjugate vaccine shows promising long-term efficacy in children

1. Children randomized to the MenA group rather than the Vi-TT group were more likely to be diagnosed with typhoid fever.

2. Overall Vi-TT vaccine efficacy was 78.3% with the highest efficacy seen for children aged 2-4 years.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Typhoid conjugate vaccines in Africa and Asia have shown high short-term efficacy, but data on long-term protection are limited. This study presents the final analysis of a trial in Malawi, spanning over 4 years, to assess vaccine efficacy over time and by age group. This randomized controlled trial aimed to evaluate the durability of protection provided by the Vi polysaccharide conjugated to tetanus toxoid (Vi-TT) vaccine against typhoid fever. The primary outcome of this study was a first occurrence of blood culture-confirmed typhoid fever, while the key secondary outcome was vaccine efficacy by age group. According to study results, a single dose of Vi-TT vaccine remained efficacious for at least 4 years. Although this study was well done, it was limited by its focus on a single geographic location, potentially affecting generalizability.

Click to read the study in The Lancet

Relevant Reading: Safety and Efficacy of a Typhoid Conjugate Vaccine in Malawian Children

In-depth [randomized-controlled trial]: Between Feb 21, 2018, and Sept 27, 2018, 29 949 patients were screened for eligibility across 4 academic hospitals in Malawi, Africa. Included were patients aged 9 months to 12 years, residing in Blantyre, Malawi, with no prior typhoid vaccination history. Altogether, 27 882 children (13 945 receiving Vi-TT and 13 937 receiving MenA) were included in the final analysis. The primary outcome of blood culture-confirmed typhoid fever occurrence was substantially lower in the Vi-TT group (39.7 cases per 100 000 person-years) than in the MenA group (182.7 cases per 100 000 person-years). The trial showed a Vi-TT efficacy of 78.3%, requiring 163 children to be vaccinated to prevent one case. Furthermore, the secondary outcome of vaccine efficacy by age group demonstrated efficacy rates ranging from 70.6% to 79.6%. Findings from this study suggest that Vi-TT vaccine provides durable efficacy for at least 4 years, supporting WHO recommendations for typhoid-endemic regions.

Image: PD

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