Background: An AIDS vaccine could play a very significant role in reversing the HIV pandemic, saving millions of lives. For a vaccine to have such an impact, it must be widely available and adopted and taken up rapidly in the countries most affected. A demand-forecasting model provides a valuable tool that can guide R&D spending decisions and identify policy actions to help achieve these goals.
Objective: To identify the key determinants of vaccine demand, model global adoption and uptake dynamics, estimate potential demand and revenues associated with future preventive AIDS vaccines, and to conduct sensitivity analyses to assess the impact of each parameter on demand.
Methods: A discrete, deterministic, linear, predictive mathematical model based on stratified population averages with a 30-year time horizon was developed to assess scenarios of future demand. This forecasting model was used to explore the effects of vaccine characteristics and a variety of regulatory, political, financial and health service factors on future demand and revenues. The intervention modelled was a preventive AIDS vaccine (efficacy: 30-90%; duration of protection: 3-5 years; in a two-dose prime-boost combination). The main outcome measure was the number of complete courses of vaccine administered.
Results: The model suggests that demand for a preventive AIDS vaccine with a medium efficacy (50%) and duration of protection (3 years) would average 68 million courses annually over a 30-year period. Under different scenarios, demand would peak at 38-152 million courses annually. On the basis of tiered pricing across public and private markets ($US2-100 per dose), these levels of peak demand would translate into $US2.5-5.5 billion in peak annual sales revenues. Private markets and high-income countries account for small volumes but large shares of projected revenues, while low-income countries account for large volumes and more modest, but still significant, sales revenues. Vaccinations to 'catch-up' those who are missed or not eligible for routine annual programmes (whether adolescent or high-risk populations) would account for 20-35% of cumulative vaccination courses across all scenarios. Demand was found to be sensitive to vaccine efficacy, duration of protection and price. Efforts to expedite regulatory review processes, improve immunization infrastructure and reduce political constraints could increase demand for an AIDS vaccine by 40 million additional courses a year compared with the medium efficacy (baseline) vaccine forecast.
Conclusions: Our model can provide vaccine developers with credible estimates of market potential for an AIDS vaccine, and with a tool that can be used to improve forecasts over time as AIDS vaccine science progresses. It can also help governments to identify and pursue those policies that could best strengthen demand and uptake of a safe and effective preventive AIDS vaccine.