Phase II multicentre double-blind randomised controlled trial of a Bivalent VaccInation against Salmonella Typhi and Paratyphi A (BiVISTA) using a controlled human infection model of paratyphoid A infection: study protocol
Abstract
Introduction: Enteric fever, primarily caused by Salmonella enterica Typhi and Salmonella enterica Paratyphi A (SPA), is endemic mainly in South Asia, disproportionately affecting school-age children. Although typhoid conjugate vaccines (TCVs) are effective and implemented in many countries, no licensed vaccine exists against paratyphoid A. Bivalent vaccines targeting both S. Typhi and SPA may address this gap. Although field efficacy trials are not considered feasible, controlled human infection models (CHIMs) offer an alternative pathway for evaluating vaccine efficacy. This will be the first efficacy study of a bivalent vaccine against typhoid and paratyphoid A using a paratyphoid CHIM.
Methods and analysis: This is a phase II multicentre, double-blind, randomised controlled trial assessing the efficacy and immunogenicity of a bivalent conjugate vaccine candidate, Serum Institute of India Typhoid Conjugate Vaccine (Bivalent) (SII-TCV(B)), against SPA using a CHIM in healthy UK adults aged 18-55 years. A total of 192 participants will be randomised 1:1 to receive either SII-TCV(B) or a licensed Vi-polysaccharide typhoid vaccine (Vi-PS). All participants will be orally challenged with S. Paratyphi A (strain NVGH308) 28 days postvaccination. Participants will be monitored closely for 14 days and treated at 14 days postchallenge or promptly on diagnosis, according to prespecified criteria. The primary objective is to evaluate vaccine efficacy of SII-TCV(B) against paratyphoid…
How strong is the evidence?
Evidence Hub reads this as a randomized trial, done in people. Its evidence level is 2 of 5 (High · randomized trial). Randomized trials of a reasonable size are the strongest single-study design. Reported size: 192 participants or records.
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