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Modeling the potential impact of typhoid conjugate vaccines

Author(s): Pitzer, V.E.; Bowles, C.C.; Baker, S.; Grenfell, Bryan T.

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Abstract: Mathematical modeling of the transmission dynamics of Salmonella Typhi allows for an evaluation of the potential impact of vaccination and a quantification of the expected direct and indirect effects of vaccines under a variety of scenarios regarding vaccine efficacy and program implementation. We developed an age-structured compartmental model that reflects the natural history and immune response to infection with Salmonella Typhi. We fit our model to data on culture-confirmed cases of typhoid fever from a variety of settings in South Asia in order to estimate important model parameters, such as the basic reproductive number (R0). We then evaluated the potential impact of routine vaccination and/or vaccination campaigns targeted at different age groups. We parameterized the vaccine efficacy and duration of protection based on data for Vi-polysaccharide and Vi-conjugate vaccines. Our model was able to reproduce the incidence pattern and age distribution of typhoid cases in Vellore, India; Kathmandu, Nepal; and Dhaka, Bangladesh for different values of R0 in these settings. Vaccination was predicted to confer substantial indirect protection in the short term, leading to a decrease in the incidence of typhoid. However, waning of vaccine-induced immunity could lead to a rebound in typhoid incidence 5-15 years after vaccine introduction. Model predictions for the overall and indirect effects of typhoid vaccination and prospects for elimination depend strongly on the role of chronic carriers in transmission. Elucidating the role of chronic carriers in transmission in different settings is a pivotal area for future epidemiological research. Our results suggest that is unlikely that typhoid can be eliminated from high incidence endemic settings through vaccination alone.
Publication Date: Apr-2014
Citation: Pitzer, V.E., Bowles, C.C., Baker, S., Grenfell, B.T. (2014). Modeling the potential impact of typhoid conjugate vaccines. International Journal of Infectious Diseases, 21 (54 - 54). doi:10.1016/j.ijid.2014.03.532
DOI: doi:10.1016/j.ijid.2014.03.532
ISSN: 1201-9712
Pages: 54 - 54
Type of Material: Conference Article
Journal/Proceeding Title: International Journal of Infectious Diseases
Version: Final published version. This is an open access article.

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