7 - The Control of Epidemics  pp. 175-193

By D. J. Daley and J. Gani

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One of the purposes of modelling epidemics is to provide a rational basis for policies designed to control the spread of a disease. This aim was already evident in Macdonald's pioneering work on malaria. In his Presidential address to the Royal Society of Tropical Medicine and Hygiene (Macdonald, 1965), he referred to the development of a prevention strategy for epidemics, malaria in particular, stating that

there is only one way of doing this—through a working model … made by assembling all we know, or more aptly, all that we believe to be significant, of the factors involved in transmission … in a form describable in mathematical terms.

A major contribution of Macdonald compared with his predecessors (he mentions Farr, Brownlee, Ross, Lotka, Kermack and McKendrick) was to pursue this approach to its

logical conclusion—of final interpretation of mathematical reasoning into non-mathematical explanations of epidemiological happenings such as could be readily understood by most practising epidemiologists.

In this spirit we consider three models for epidemics to illustrate possible prevention policies of control by (a) education, (b) immunization, and (c) screening and quarantine. We could add that modelling is of vital importance in evaluating the likely effects of spreading a disease deliberately as a means of biological control, as with myxomatosis or the calicivirus to reduce the rabbit population in Australia.

Often the data available to decision makers are inadequate, as for example in the case of HIV/AIDS in Africa or South East Asia. Yet policies need to be formulated, if only on the basis of rough qualitative measures.