Typhoid

IVI typhoid model

Lead modeller: Jong-Hoon Kim

Institution(s): International Vaccine Institute (IVI)

Brief description of model:

The model utilizes a static framework to estimate the impact of the typhoid conjugate vaccine on various health outcomes, including the number of cases, deaths, years of life lost (YLLs), and disability-adjusted life years (DALYs). The impact of the vaccine is evaluated by first calculating the reduction in cases through vaccination and deaths, YLLS, DALYs were derived from the reduced number of cases. The model incorporates both the direct effects of vaccination on individuals who receive the vaccine and the indirect effects on the wider community through herd immunity. The model adjusts for expected changes in annual incidence, which generally improve with advancements in water quality, sanitation, and hygiene. The parameters of the model, such as case distribution by severity, illness duration, vaccine coverage, and the demographics of the target population, is frequently updated to reflect the latest research. The impact of vaccine was explored over a broad spectrum of values for uncertain parameters.

Key publication(s):

Link to publicly available code (where available):

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Yale typhoid model

Lead modeller: Virginia Pitzer
Link to all modelling group members

Institution(s): Yale

Brief description of model:

The model predicts vaccine impact on typhoid incidence using a deterministic transmission dynamic model. It accounts for important features of typhoid epidemiology, e.g. immunity to clinical versus subclinical infection, and the prevalence and contribution of chronic carriers to transmission. It does not distinguish between short- versus long-cycle (i.e. water-borne) transmission because these two transmission routes are not identifiable from the annual incidence estimates used for model fitting, and the bacteria are short-lived in the environment. Dynamic model output on the incidence rate of typhoid fever (per 100,000 person-years) is multiplied by the country-specific demography to produce final estimates.

Key publication(s):

Link to publicly available code (where available):