Efficacy and Safety of Tetanus-Toxoid Conjugate Typhoid Vaccine (Vi-TT) in Children and Adolescents: A Systematic Review and Meta-Analysis.

Typhoid fever is a major cause of morbidity and mortality in developing countries. This review assessed the efficacy, safety, and immunogenicity of the tetanus toxoid conjugate typhoid vaccine (Vi-TT) in children and adolescents. Randomized controlled trials involving Vi-TT in individuals under 18 were included. Eligible studies were screened, and quality was assessed using the Cochrane Risk of Bias-2 tool. Meta-analysis was conducted with RevMan Web. Four trials with 111 481 children found the risk of blood culture-confirmed typhoid fever after Vi-TT to be 0.18 (95% CI [0.13, 0.24]) compared with nontyphoid vaccines. Adverse event rates were similar, with a serious adverse event risk of 0.82 (95% CI [0.71, 0.95]) within six months. Seroconversion was 58.04 times higher at 28 days and 21.80 times higher after 18 months postvaccination (95% CIs [36.24, 92.96] and [15.44, 30.80], respectively). One trial had a high risk of bias, so sensitivity analysis was performed with and without it. GRADE assessment showed strong evidence that Vi-TT reduces typhoid risk without significant safety concerns. Seroconversion declined over time but remained significantly higher after 18 months. This concludes that Vi-TT is safe and effective for children and adolescents, and is recommended for vaccination in endemic areas.