ActiveInfection & ImmunityNIHR-supported projectPregnancy, Children & Inherited Conditions
An observer-blind participant-blind randomised controlled trial to assess the immunogenicity and efficacy of SII Typhoid Conjugate Vaccine (Bivalent) against Salmonella Paratyphi A using a human challenge model of paratyphoid infection
Recipient organisationNIHR Wellcome Trust Southampton Clinical Research Facility
NIHR supportRecorded as supported by this research centre
PeriodJan 2025 — Sept 2027
In plain English
AI plain-English summary
Every year, 3.8 million cases of enteric fever are caused by *Salmonella Paratyphi A* — and there is no licensed vaccine against it. This matters because enteric fever, which also includes typhoid, spreads through contaminated food and water in regions with poor sanitation. While effective vaccines exist for typhoid, *Paratyphi A* has been left out, leaving millions vulnerable to high fevers, abdominal pain, and potentially fatal complications. The Serum Institute of India has developed a bivalent vaccine (SII-TCV(B)) that targets both typhoid and paratyphoid A. This trial will test whether it actually prevents paratyphoid infection using a controlled human infection model — volunteers receive the vaccine, then deliberately ingest the bacteria under close monitoring. If the vaccine works, it could become the first licensed protection against paratyphoid A, filling a critical gap in enteric fever control. That would directly reduce illness and death in regions where clean water and sanitation remain scarce. The study will also clarify how the human immune system builds protection against *Paratyphi A*, which could guide future vaccine design. The World Health Organization has endorsed this approach as the best way to evaluate paratyphoid vaccine candidates.
View original technical description
Typhoid and Paratyphoid fever are forms of an illness called enteric fever. Their names come from the bacteria that cause them: Salmonella Typhi (typhoid) and Salmonella Paratyphi (paratyphoid, mostly caused by S. Paratyphi A). Enteric fever can cause high temperatures, headache, muscle and joint aches, abdominal pain, constipation and feeling generally unwell. If severe or left untreated, it can result in complications, including long-term carriage of the bacteria or even death.There are approximately 13 million cases of enteric fever every year, with 3.8 million of these due to paratyphoid infection. It spreads by the faeces of an infected person, typically through contaminated water or food. It is prevalent in regions of the world where people have inadequate access to clean water and sanitation.Effective vaccines against S. Typhi already exist, but there are no licensed vaccines against S. Paratyphi A. The Serum Institute of India (SII) has developed a vaccine targeting both Salmonella Typhi and Salmonella Paratyphi A, the SII-TCV(B), given as an injection in the upper arm muscle. It was tested in humans, showing it is safe. In this study, we will test if this vaccine: 1. could prevent paratyphoid A, using a controlled human infection model (CHIM), and 2. induces similar response as a comparator vaccine (a licensed vaccine against S. Typhi). We will also use this study to better understand how we develop protection against paratyphoid A.In this CHIM, participants are given a vaccine [SII-TCV(B) or comparator], later they are given a dose of S. Paratyphi A which can cause disease. They are closely monitored and treated 14 days after drinking the bacteria, or sooner, if they become unwell. This model of studying vaccines has been safely undertaken by participants in previous Oxford Vaccine Group studies, and it was recommended by the World Health Organisation (WHO) to study the efficacy of a paratyphoid A vaccine candidate.
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