Two New Typhoid Vaccines Show Efficacy in Reducing Rates of Stool Shedding

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Prior vaccination with Vi vaccines, or natural infection, reduces onward transmission of <i>S Typhi</i>.
Prior vaccination with Vi vaccines, or natural infection, reduces onward transmission of S Typhi.

Shedding of Salmonella Typhi or Paratyphi in the stool or urine can lead to contamination of food or water supplies, but vaccination with Vi-polysaccharide or Vi-tetanus-toxoid conjugate vaccine successfully reduced stool shedding of S Typhi and is likely to reduce future transmission of disease, according to findings published in Clinical Infectious Diseases.

Vaccines that can reduce bacterial shedding as well as protect against active infection are more effective in interrupting disease transmission and providing indirect protection in exposed persons compared with exposed individuals who have not been vaccinated. However, data are limited concerning the effectiveness of vaccination or prior exposure on stool shedding. In this report, the researchers highlighted 6 S Typhi or Paratyphi human challenge studies conducted between 2011 and 2017, in which participants were either unvaccinated or vaccinated with 1 of 4 vaccines: Vi-polysaccharide vaccine, Vi-tetanus-toxoid conjugate vaccine, live oral Ty21a vaccine, or an experimental vaccine (M01ZH09).

A total of 4934 stool samples were collected from 430 volunteers and used in the analysis. Results showed that participants who received Vi-polysaccharide vaccine or Vi-tetanus-toxoid conjugate vaccine had less shedding that those who were unvaccinated (odds ratio [OR], .34; 95% CI, .15-.77; P =.010 and OR, .41; 95% CI, .19-.91; P =.029 for Vi-PS and Vi-TT, respectively). There was also a nonsignificant reduction in shedding with the Ty21a vaccine (OR, .57; 95% CI, .27-1.20; P =.140), and participants with previous exposure to S Typhi also had less shedding than those who were never exposed (OR, .30; 95% CI, .1-.8; P =.016). In addition, the odds of shedding in participants exposed to S Typhi were increased 2-fold compared with in participants exposed to S Paratyphi (OR, 1.97; 95% CI, 1.00-3.88; P =.049).

“We have performed the first detailed model of shedding dynamics in the context of controlled typhoid and paratyphoid challenge and provide evidence for efficacy of new and existing typhoid vaccines (Vi-polysaccharide and Vi-tetanus-toxoid conjugate vaccines) in reducing rates of shedding,” the study authors concluded.

Reference

Gibani MM, Voysey M, Jin C, et al. The impact of vaccination and prior exposure on stool shedding of Salmonella typhi and Salmonella paratyphi in 6 controlled human infection studies [published online September 25, 2018]. Clin Infect Dis. doi: 10.1093/cid/ciy670

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