Mathematical Models and the Design of Public Health Policy: Hiv and Antiviral Therapy

Abstract

Antiviral therapy acting to increase the incubation period of HIV-1, without significantly reducing infectiousness, will necessarily increase the prevalence of infection, unless accompanied by appropriate levels of behaviour change. However, the number of AIDS-related deaths may decline despite a large increase in numbers of seropositives, if the latter is balanced by an increase in the average life-span of an infected individual. In a homogeneous population, treatment will be of benefit to both the individual and the community if the basic reproductive rate of the disease is high, provided that the coverage and efficacy are also high. However, therapy may be of detriment to the community (i.e., produce an increase in the number of AIDS deaths) under a combination of low drug efficacy and high coverage or vice versa, if the basic reproductive rate is low. In a behaviourally heterogeneous population with proportionate mixing, the outcome of treatment is extremely sensitive to the rate of cessation of sexual activity. Within certain parameter combinations, the sensitivity of the system to the rate of cessation of sexual activity can cause a larger decrease in population size at higher basic reproductive rates. This is in direct contrast to the homogeneous case, where the outcome of therapy is less likely to be perverse at higher values of the basic reproductive rate. The conclusions of this paper are not in conflict with the moral imperative of providing treatment for individuals infected with HIV.