Prevention investment needed now to ensure long-term affordability of treatment

Treatment programmes which fail to be combined with effective prevention programmes will have little impact on HIV incidence over the next 15 years, according to projections published today by Harvard School of Public Health in the online journal Public Library of Science Medicine. Whilst combined programmes could avert 29 million new infections and 10 million deaths by 2020 in Africa, a narrow focus on treatment would result in only 9 million new infections averted during the same period, the research group says.

"Only effective prevention will make treatment affordable in the long run,” warn the authors.

The modelling exercise was led by Joshua Solomon of Harvard School of Public Health and colleagues from the Futures Group, UNAIDS and the Global Fund to Fight AIDS. They used models already developed for Africa by UNAIDS that assume an increase in annual infections from 2.4 million to 3.7 million by 2020 and an increase in deaths from 1.8 million to 2.6 million between 2004 and 2020, and calculated the interaction between several different packages of interventions:

• Comprehensive prevention activities including voluntary counselling and testing, behaviour change programmes with at-risk groups, prevention of mother to child transmission, condom distribution and promotion. Risk behaviours are maintained at current levels in this model, and the researchers also examined the effects of packages that were 25%, 50% and 75% as effective as the full package in the context of treatment provision, in order to analyse the effect of a shift of emphasis from prevention to treatment.
• Treatment coverage reaches 50% of those eligible by 2005, 80% by 2010 and is maintained at this level to 2020, with a 99% reduction in transmissibility and a halving in annual partnership numbers, but also a 10% reduction in condom use.

Assuming 80% treatment coverage by 2010 without any changes in behaviour, the annual infection rate could be reduced by 6%, the researchers predict. Mortality would initially decline by one-third but would drift back to baseline over time. If treatment efforts are less successful, and prevention efforts do not improve, the number of new infections will rise to 4.3 million per year by 2020 – above the rate predicted without treatment. Even if the assumption of reduced condom use is removed from this model, new infections are reduced by only 2% a year in this scenario.

A greater investment in prevention would halve new infections by 2020, but at the price of negligible changes in mortality in the medium and long-term.

Scaling up prevention and treatment at the same time would reduce the rate of new infections by up to three-quarters and annual mortality by 47% by 2020 (with the majority of this reduction in mortality driven by reduction in new infections rather than treatment effects). Total prevalence could be reduced by up to 55% in the most optimistic scenario, but if the focus is limited to treatment expansion, prevalence could rise by up to 27% by 2020.

“The total number of infections averted through a combined response would be 29 million over the period 2004 to 2020 if treatment enhances prevention, a benefit that is ten times greater than that of a strategy which focuses on treatment only, even with optimal assumptions, and 51% greater than that of a strategy which focuses on (less effective) prevention alone”.

The authors note that combining treatment with the most optimistic prevention efforts could reduce the numbers requiring antiretroviral treatment in 2020 by 5 million.

“Without effective prevention programs, we project that the number of people receiving treatment will grow to 6.3 million by 2010 and up to 9.2 million by 2020 in Africa alone to achieve 80% coverage of those in urgent need. Meeting this need would require a tremendous increase in financing, human capacity and infrastructure that might not be attainable.”

“If effective prevention programs are combined with treatment programs, the same level of 80% ART coverage would be achieved by treating 5.8 million in 2010 and 4.2 million in 2020. In other words, the same goal could be attained at a far lower treatment cost and with a much greater chance of sustainability.”