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Clin Infect Dis. 2018 Sep 25. doi: 10.1093/cid/ciy670. [Epub ahead of print]

The Impact of Vaccination and Prior Exposure on Stool Shedding of Salmonella Typhi and Salmonella Paratyphi in 6 Controlled Human Infection Studies.

Author information

1
Oxford Vaccine Group, Department of Paediatrics, University of Oxford.
2
Nuffield Department of Primary Care Health Sciences, University of Oxford, United Kingdom.
3
Oxford University Hospitals, National Health Service Foundation Trust, United Kingdom.
4
Medical Research Council Human Immunology Unit, Radcliffe Department of Medicine, University of Oxford, United Kingdom.
5
Translational Gastroenterology Unit, University of Oxford, United Kingdom.
6
Malawi-Liverpool-Wellcome Trust Clinical Research Programme, Blantyre.
7
Institute for Infection and Global Health, University of Liverpool, United Kingdom.
8
Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut.
9
Nuffield Department of Medicine, University of Oxford, United Kingdom.
10
Center for Vaccine Development, University of Maryland School of Medicine, Baltimore.
11
Department of Infection, Immunity and Cardiovascular Disease, University of Sheffield.
12
National Institute for Health Research Oxford Biomedical Research Centre, United Kingdom.

Abstract

Background:

Shedding of Salmonella Typhi or Paratyphi in the stool or urine leads to contamination of food or water, which is a prerequisite for transmission of enteric fever. Currently, there are limited data on the effect of vaccination or prior exposure on stool shedding.

Methods:

Six Salmonella Typhi or Paratyphi human challenge studies were conducted between 2011 and 2017. Participants were either unvaccinated or vaccinated with 1 of 4 vaccines: Vi-polysaccharide (Vi-PS), Vi-tetanus-toxoid conjugate vaccine (Vi-TT), live oral Ty21a vaccine, or an experimental vaccine (M01ZH09). Daily stool cultures were collected for 14 days after challenge.

Results:

There were 4934 stool samples collected from 430 volunteers. Participants who received Vi-PS or Vi-TT shed less than unvaccinated participants (odds ratio [OR], 0.34; 95% confidence interval [CI], 0.15-0.77; P = .010 and OR, 0.41; 95% CI, 0.19-0.91, P = .029 for Vi-PS and Vi-TT, respectively). Higher anti-Vi immunoglobulin G titers were associated with less shedding of S. Typhi (P < .0001). A nonsignificant reduction in shedding was associated with Ty21a vaccine (OR, 0.57; 95% CI, 0.27-1.20; P = .140). Individuals previously exposed to S. Typhi shed less than previously unexposed individuals (OR, 0.30; 95% CI, 0.1-0.8; P = .016). Shedding of S. Typhi was more common than S. Paratyphi.

Conclusions:

Prior vaccination with Vi vaccines, or natural infection, reduces onward transmission of S. Typhi. Field trials of Vi-TT should be designed to detect indirect protection, reflecting the consequence of reduced stool shedding observed in the human challenge model.

PMID:
30252031
DOI:
10.1093/cid/ciy670
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