and has been prequalified by WHO for purchase by UN agencies.
The WHO Strategic Advisory Group of Experts on Immunization has recommended that, for programmatic and epidemiological reasons, the vaccine should be started at 9 months of age, coincident with the 9 month Expanded Programme on Immunization visit in many countries. A phase 3 randomised, controlled trial has shown that the vaccine was safe and highly immunogenic (seroconversion, 98%; geometric mean titre, 1937 [95% CI 1785–2103]) in children (n=327) aged 6–23 months.
This vaccine has also been shown in an interim analysis of an individually randomised efficacy trial among children in Nepal to confer 82% protection against typhoid disease.
To better understand the ability of this vaccine to confer protection, including herd protection, under circumstances of mass immunisation, we did a cluster-randomised, controlled, clinical trial of Vi-TT vaccine in urban Bangladesh.