Critique of Early Models of the Demographic Impact of HIV/AIDS in Sub-Saharan Africa Based on Contemporary Empirical Data from Zimbabwe

Simon Gregson, Imperial College
Constance Nyamukapa, Biomedical Research & Training Institute
Benjamin A. Lopman, Imperial College
Phyllis Mushati, Biomedical Research & Training Institute
Geoff P Garnett, Imperial College London
Roy M Anderson, Imperial College London

Soon after HIV/AIDS emerged in sub-Saharan Africa in the 1980s, it was recognised that the full demographic impact might not become apparent for more than 20 years. Early mathematical models varied in their predictions of the severity of the impact on population growth. In pessimistic scenarios, reductions in rates of natural increase of 3.5% per annum to below zero were envisaged but little impact on dependency ratios was expected. Twenty years into the epidemic in eastern Zimbabwe, where HIV prevalence peaked at around 33% in the worst-affected areas, HIV/AIDS reduced the rate of natural increase from 2.9% to 1.0% per annum. The dependency ratio fell from 1.21 to 0.78, the impact of AIDS mortality being outweighed by fertility decline. In hindsight, the more pessimistic early models over-estimated the impact on population growth by over-extrapolating initial HIV growth rates or not allowing for heterogeneity in transmissibility and sexual risk behaviour.