Elsevier

Vaccine

Volume 33, Supplement 3, 19 June 2015, Pages C42-C54
Vaccine

Review
A review of typhoid fever transmission dynamic models and economic evaluations of vaccination

https://doi.org/10.1016/j.vaccine.2015.04.013Get rights and content
Under a Creative Commons license
open access

Highlights

  • There are relatively few dynamic models or economic analyses of typhoid vaccination.

  • The relative contribution of carriage to transmission is a key uncertainty.

  • Published economic analyses use static models that omit indirect protection of vaccines.

  • Nevertheless, vaccines appear highly cost-effective against WHO criteria in high-incidence settings.

  • No economic model was found to compare vaccine and sanitation.

Abstract

Despite a recommendation by the World Health Organization (WHO) that typhoid vaccines be considered for the control of endemic disease and outbreaks, programmatic use remains limited. Transmission models and economic evaluation may be informative in decision making about vaccine programme introductions and their role alongside other control measures. A literature search found few typhoid transmission models or economic evaluations relative to analyses of other infectious diseases of similar or lower health burden.

Modelling suggests vaccines alone are unlikely to eliminate endemic disease in the short to medium term without measures to reduce transmission from asymptomatic carriage. The single identified data-fitted transmission model of typhoid vaccination suggests vaccines can reduce disease burden substantially when introduced programmatically but that indirect protection depends on the relative contribution of carriage to transmission in a given setting. This is an important source of epidemiological uncertainty, alongside the extent and nature of natural immunity.

Economic evaluations suggest that typhoid vaccination can be cost-saving to health services if incidence is extremely high and cost-effective in other high-incidence situations, when compared to WHO norms. Targeting vaccination to the highest incidence age-groups is likely to improve cost-effectiveness substantially. Economic perspective and vaccine costs substantially affect estimates, with disease incidence, case-fatality rates, and vaccine efficacy over time also important determinants of cost-effectiveness and sources of uncertainty. Static economic models may under-estimate benefits of typhoid vaccination by omitting indirect protection.

Typhoid fever transmission models currently require per-setting epidemiological parameterisation to inform their use in economic evaluation, which may limit their generalisability. We found no economic evaluation based on transmission dynamic modelling, and no economic evaluation of typhoid vaccination against interventions such as improvements in sanitation or hygiene.

Keywords

Typhoid
Typhoid fever
Enteric fever
Salmonella Typhi
Vaccination
Immunisation
Transmission dynamics
Mathematical model
Economic evaluation
Cost utility analysis

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