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PLoS Negl Trop Dis. 2014 Jan 9;8(1):e2642. doi: 10.1371/journal.pntd.0002642. eCollection 2014.

Predicting the impact of vaccination on the transmission dynamics of typhoid in South Asia: a mathematical modeling study.

Author information

  • 1Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, United States of America ; Fogarty International Center, National Institutes of Health, Bethesda, Maryland, United States of America.
  • 2Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, United States of America ; Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America.
  • 3The Hospital for Tropical Diseases, Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, Ho Chi Minh City, Vietnam ; Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, Oxford University, Oxford, United Kingdom ; The London School of Hygiene and Tropical Medicine, London, United Kingdom.
  • 4Department of Gastrointestinal Sciences, Christian Medical College, Vellore, Tamil Nadu, India.
  • 5Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America ; The Hospital for Tropical Diseases, Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, Ho Chi Minh City, Vietnam ; Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, Oxford University, Oxford, United Kingdom.
  • 6Fogarty International Center, National Institutes of Health, Bethesda, Maryland, United States of America ; Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America.

Abstract

BACKGROUND:

Modeling of the transmission dynamics of typhoid allows for an evaluation of the potential direct and indirect effects of vaccination; however, relevant typhoid models rooted in data have rarely been deployed.

METHODOLOGY/PRINCIPAL FINDINGS:

We developed a parsimonious age-structured model describing the natural history and immunity to typhoid infection. The model was fit to data on culture-confirmed cases of typhoid fever presenting to Christian Medical College hospital in Vellore, India from 2000-2012. The model was then used to evaluate the potential impact of school-based vaccination strategies using live oral, Vi-polysaccharide, and Vi-conjugate vaccines. The model was able to reproduce the incidence and age distribution of typhoid cases in Vellore. The basic reproductive number (R 0) of typhoid was estimated to be 2.8 in this setting. Vaccination was predicted to confer substantial indirect protection leading to a decrease in the incidence of typhoid in the short term, but (intuitively) typhoid incidence was predicted to rebound 5-15 years following a one-time campaign.

CONCLUSIONS/SIGNIFICANCE:

We found that model predictions for the overall and indirect effects of vaccination depend strongly on the role of chronic carriers in transmission. Carrier transmissibility was tentatively estimated to be low, consistent with recent studies, but was identified as a pivotal area for future research. It is unlikely that typhoid can be eliminated from endemic settings through vaccination alone.

PMID:
24416466
[PubMed - indexed for MEDLINE]
PMCID:
PMC3886927
Free PMC Article
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