Cost-Effectiveness, Affordability, and Uncertainty
The GAVI alliance has recently extended its support for accelerating the introduction of new and underused vaccines, including hepatitis B vaccines, to low income countries up to 2015. However, since there is no guaranteed long-term support beyond 2015 and each recipient country is required to co-finance its immunization program, poorest countries will have to consider the financial sustainability of their vaccination programs. In doing so, there will inevitably be uncertainty surrounding the real-world benefits of vaccination and the resources required to implement and sustain programs, particularly in settings with weak health infrastructure, which will further complicate budget-related decisions. In this context, decision-makers will likely benefit from additional information on program affordability and cost-effectiveness that accounts for these uncertainties. In part, this has been addressed by summarizing cost-effectiveness results using cost-effectiveness acceptability curves; these curves show the probability that a program will be cost-effective as a function of different thresholds for acceptable cost-effectiveness ratios. However, one limitation of this approach is that total resource constraints for a program are not considered explicitly. The cost-effectiveness affordability curve proposed by a previous study addresses this limitation by presenting the probabilities that a program is simultaneously cost-effective and affordable as a function of both the threshold cost–effectiveness ratios and budgetary constraints.
To illustrate the usefulness of providing decision-makers with information on affordability and cost-effectiveness while formally accounting for uncertainty, we applied this approach to a real-world policy example: the infant vaccination program against hepatitis B in the Gambia. In doing so, we developed a mathematical model to synthesize the available data and re-evaluate the cost-effectiveness of the hepatitis B program. We then derived cost-effectiveness affordability curves based on Monte Carlo simulation results, by varying both cost-effectiveness thresholds and budget constraints and counting the proportion of simulation outcomes that meet both criteria. This initial analysis shows that in the face of uncertainties about both the health and economic consequences of a vaccine program, as well as the availability and magnitude of resources needed to fund the program, cost-effectiveness affordability curves can provide useful graphical information to decision-makers about the probability that a program will be both cost-effective and affordable—considerations equally relevant, but rarely assessed together.
We are applying this framework to other new vaccines, such as rotavirus and HPV, although we do recognize that the method may be limited in fully addressing a resource allocation problem in general, because it focuses on a fixed budget for a single new vaccine. CHDS investigators are seeking funding to engage in two areas of related work. One area of work we are pursuing assumes that the budget constraint for each new vaccine is indeed vaccine-specific. However, if this is not the case, fully evaluating a vaccination program’s affordability requires a more comprehensive approach explicitly considering the affordability of other competing vaccination programs under a shared budget. Thus, the second area of work we are pursuing assumes that the budget constraint is the total portfolio costs of a group of vaccines. This work requires estimation of the probability that each portfolio will be affordable over a range of budget levels, by iterating Monte Carlo simulations of all relevant interventions and calculating the joint distribution of the total portfolio costs and effectiveness.