TyVOID

The overall objective of this proposal is to provide new evidence to support the elimination of typhoid from regions of the world where there is a substantial burden that threatens the health of children and young people.

This will be achieved, with co-funding from the Bill&Melinda Gates Foundation, by a) assessing in a population of over 350,000 inhabitants in South Asia, whether efficacy of the WHO-approved typhoid conjugate vaccine in children is lower in the medium-term than in the initial 2-year period after vaccination.

This will provide evidence for need for booster doses, addressing a key question from WHO SAGE, 2017. b) assessing the decay in total and functional anti-typhoid Vi and CdtB antibodies in children 3 -4-years after vaccination, and comparing community-based typhoid clinical- and sero-incidence with these immune responses; this will help to identify correlates of medium-term protection for typhoid in two different endemic settings to further inform the need for and timing of booster doses of vaccine. c) predicting the future impact of typhoid vaccination in two endemic settings using mathematical models fitted to the first available data on medium-term efficacy, and to evaluate the potential cost-effectiveness of adding booster doses to the vaccine schedule.