Use of vaccines as probes to define disease burden

Abstract

Vaccine probe studies have emerged in the past 15 years as a useful way to characterise disease. By contrast, traditional studies of vaccines focus on defining the vaccine effectiveness or efficacy. The underlying basis for the vaccine probe approach is that the difference in disease burden between vaccinated and unvaccinated individuals can be ascribed to the vaccine-specific pathogen. Vaccine probe studies can increase understanding of a vaccine's public health value. For instance, even when a vaccine has a seemingly low efficacy, a high baseline disease incidence can lead to a large vaccine-preventable disease burden and thus that population-based vaccine introduction would be justified. So far, vaccines have been used as probes to characterise disease syndromes caused by Haemophilus influenzae type b, pneumococcus, rotavirus, and early infant influenza. However, vaccine probe studies have enormous potential and could be used more widely in epidemiology, for example, to define the vaccine-preventable burden of malaria, typhoid, paediatric influenza, and dengue, and to identify causal interactions between different pathogens.

Figure. Proportions of different categories of pneumonia attributable to pneumococcus (left) and the effect of pneumococcal vaccine (right)

On the left, for the more specific outcomes towards the top of the triangle, vaccine efficacy is higher, whereas for the more sensitive outcomes at the base of the triangle, the vaccine preventable disease incidence is higher, as is the public health utility of vaccine.