Modelling indirect protection from typhoid conjugate vaccines in the TyVAC-Bangladesh trial.

Authors

Jo Walker, Farhana Khanam, Xinxue Liu, Merryn Voysey, Md Asif Ahsan, Md Golam Firoj, Nazmul Hasan Rajib, Prasanta Kumar Biswas, Andrew Pollard, K Zaman, Firdausi Qadri, John D Clemens, Virginia Pitzer

Published in

Epidemiology and infection. Volume 154. Pages e147. Nov 09, 2026. Epub Nov 09, 2026.

Abstract

In the TyVAC-Bangladesh cluster-randomized trial, a dose of typhoid conjugate vaccine (TCV) in children aged 9 months to <16 years conferred strong protection against typhoid fever. However, indirect protection among unvaccinated residents was modest and not statistically significanct, raising questions about TCV's effectiveness against Salmonella Typhi transmission and ability to induce herd effects in endemic settings. We hypothesize that this low observed indirect protection could be explained by some combination of transmission across cluster boundaries, limited vaccine protection against infection, and insufficient vaccine coverage. To evaluate these hypotheses, we simulated the trial using a primary transmission dynamic model calibrated against clinical surveillance data, and an alternative model incorporating serological data. Vaccinating 64% of eligible children (the observed trial coverage) induced up to 67% and 54% indirect protection in the primary and alternative models, respectively, depending on the transmissibility of chronic carriers and TCV efficacy against S. Typhi infection. The trial results were consistent with 15% to 85% TCV efficacy against infection in the primary model, and 60% to 90% protection in the alternative model. If adults were vaccinated at the same coverage level as children, we estimate that indirect protection would have increased from 19% to 40%-57%. These findings suggest that TCV confers protection against transmission from acute S. Typhi infections, and that the low indirect protection observed in the TyVAC-Bangladesh trial can be explained by transmission from unvaccinated adults.

PMID:
43000950
Bibliographic data and abstract were imported from PubMed on 09 Nov 2026.

Read full publication at:
Please sign in to see all details.

Stats

1-terrible, 9-excellent. How would you rate this publication? Sign in in to submit your rating.

Post a comment

You need to be signed in to post comments. You can sign in here.

Comments

There are no comments yet.