Synthesizing epidemiological and economic optima for control of immunizing infections

Wednesday, 18th of December 2013

[source]Proceedings of the National Academy of Sciences, USA[|source]

Traditionally, the main economic benefit of disease eradication was envisaged in terms of cessation of vaccination after interruption of infection. In a context of current focus on potential elimination of measles and polio, it is timely to add an economic component to the basic epidemiological theory of herd immunity. Assuming that herd immunity is maintained at eradication levels, the economic benefits of eradication are then simply the health benefits derived from preventing disease.

In this article, the authors document that introducing the costs of infection and vaccination dramatically alters the conditions under which it is optimal to eliminate a disease. When the cost of infection is finite, the optimal vaccination coverage is independent of transmission and is set at the level where the benefit of lower cost of infection is balanced against the cost of increasing coverage. They argue that when postelimination cessation of vaccination is not an option, it may even be optimal for a country to vaccinate at a level exceeding the critical vaccination coverage rate in the presence of incoming infecteds, if the costs of disease are high enough and vaccination is affordable enough.  More details technical details are available at:  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3161560/

Abstract

Epidemic theory predicts that the vaccination threshold required to interrupt local transmission of an immunizing infection like measles depends only on the basic reproductive number R₀ and hence transmission rates. When the search for optimal strategies is expanded to incorporate economic constraints, the optimum for disease control in a single population is determined by relative costs of infection and control, rather than transmission rates. Adding a spatial dimension, which precludes local elimination unless it can be achieved globally, can reduce or increase optimal vaccination levels depending on the balance of costs and benefits. For weakly coupled populations, local optimal strategies agree with the global cost-effective strategy; however, asymmetries in costs can lead to divergent control optima in more strongly coupled systems—in particular, strong regional differences in costs of vaccination can preclude local elimination even when elimination is locally optimal. Under certain conditions, it is locally optimal to share vaccination resources with other populations.