Over the next decade, several new vaccines will be considered for universal use against infectious diseases of major public health importance. Public health decision makers will need to make choices between vaccines and among various health interventions. New vaccines are more expensive than the traditional dollars-and-cents vaccine costs, while countries increasingly have to bear the full cost of vaccination programmes. Because not all evidence is available to explore the impact of interventions under different scenarios, cost-effectiveness analyses (CEAs) of vaccination programmes tend to be based on mathematical modelling, which should yield a framework and help synthesize information from many sources and also help extrapolate data beyond available data (for example, clinical trials). Given the complexity and the importance of these tools, and to accurately inform vaccine policy makers at the country level, a critical appraisal of these tools' robustness and limitations as well as of the generalizability of model estimates to local contexts needs to be conducted and documented before results are accepted.
A recent systematic literature review showed that cost-effectiveness (CE) has become an increasingly important factor for stakeholders who need to make decisions about adding a new vaccine into national immunization programmes versus alternative uses of resources [1
]. However, the same study also pointed out that the majority of these studies were done in high-income countries, while in low- and middle-income countries (LMICs), where fewer studies are performed, economic evaluations have a more limited role in the decision-making process.
The need for increased guidance on CE was clearly identified in a stakeholder review conducted on the World Health Organization's (WHO's) normative role in immunization [2
]. Country-level decision makers, particularly those from LMICs, discussed the lack of guidance on the criteria used to assess the model structure, assumptions, robustness and limitations of economic decision-making tools [3
]. As a response to these needs, WHO embarked on a series of consultations to assess economic analytical tools to support vaccine introduction decisions for pneumococcal, rotavirus and human papillomavirus vaccines [4
] Considering that a malaria vaccine is undergoing pivotal phase 3 evaluation, WHO is evaluating impact models that can inform decisions about the use of combinations of antimalarial interventions. The objectives of these assessments are to provide decision makers with a menu of existing CE tools for vaccines and a transparent overview of their characteristics rather than to recommend a single model. The goals of these consultations are to provide policy makers in LMICs with information about the feasibility of applying these models to aid their own decision making, as well as with guidance for interpreting the results from these and similar studies. Country-level decision making for the introduction decisions regarding new vaccines is a complex process that needs to take into account several factors, such as local information on patterns of disease transmission, effective coverage and costs per dose, as these parameters are often the ones that drive the outcomes of the CEA. In addition, the characteristics of the healthcare system and issues pertinent to financing, affordability and sustainability should be important elements in the decision-making process. Moreover, decision makers often experience substantial pressure from many stakeholders and "vaccine advocates" who contribute to the interpretation of the available evidence. The conclusions of the WHO consultations to assess the vaccine economic analytical tools mentioned above led us to argue that relying on CEA results from only a single modelling exercise is not desirable [4
]. We also reiterate that conducting sensitivity analyses is critical to comprehending the modelling and CEA outcomes. After a critical review of the outcomes of these consultations, the WHO Quantitative Immunization and Vaccine-Related Research Committee endorsed these statements [7