Simulation of the cost-effectiveness of malaria vaccines

Abstract

Background: A wide range of possible malaria vaccines is being considered and there is a need to identify which vaccines should be prioritized for clinical development. An important element of the information needed for this prioritization is a prediction of the cost-effectiveness of potential vaccines in the transmission settings in which they are likely to be deployed. This analysis needs to consider a range of delivery modalities to ensure that clinical development plans can be aligned with the most appropriate deployment strategies.

Methods: The simulations are based on a previously published individual-based stochastic model for the natural history and epidemiology of Plasmodium falciparum malaria. Three different vaccine types: pre-erythrocytic vaccines (PEV), blood stage vaccines (BSV), mosquito-stage transmission-blocking vaccines (MSTBV), and combinations of these, are considered each delivered via a range of delivery modalities (Expanded Programme of Immunization - EPI-, EPI with booster, and mass vaccination combined with EPI). The cost-effectiveness ratios presented are calculated for four health outcomes, for assumed vaccine prices of US$ 2 or US$ 10 per dose, projected over a 10-year period.

Results: The simulations suggest that PEV will be more cost-effective in low transmission settings, while BSV at higher transmission settings. Combinations of BSV and PEV are more efficient than PEV, especially in moderate to high transmission settings, while compared to BSV they are more cost-effective in moderate to low transmission settings. Combinations of MSTBV and PEV or PEV and BSV improve the effectiveness and the cost-effectiveness compared to PEV and BSV alone only when applied with EPI and mass vaccinations. Adding booster doses to the EPI is unlikely to be a cost-effective alternative to delivering vaccines via the EPI for any vaccine, while mass vaccination improves effectiveness, especially in low transmission settings, and is often a more efficient alternative to the EPI. However, the costs of increasing the coverage of mass vaccination over 50% often exceed the benefits.

Conclusion: The simulations indicate malaria vaccines might be efficient malaria control interventions, and that both transmission setting and vaccine delivery modality are important to their cost-effectiveness. Alternative vaccine delivery modalities to the EPI may be more efficient than the EPI. Mass vaccination is predicted to provide substantial health benefits at low additional costs, although achieving high coverage rates can lead to substantial incremental costs.

Figure 1

Effect of initial efficacy on cost-effectiveness of PEV by transmission setting and delivery modality*. Results obtained assuming a vaccine half-life of 10 years, homogeneity value of 10, and vaccine price of US$2. EPI & Campaigns means EPI with 70% mass vaccination. *data for EIR in some cases are not shown in the figure due to a scale problem.

Figure 2

Effect of initial efficacy on cost-effectiveness of BSV by transmission setting and delivery modality. Results obtained assuming a vaccine half-life of 10 years, homogeneity value of 10, and vaccine price of US$2. EPI & Campaigns means EPI with 70% mass vaccination.

Figure 3

Effect of initial efficacy on cost-effectiveness of all vaccines delivered via EPI by transmission setting*. Results obtained assuming a vaccine half-life of 10 years and homogeneity value of 10, and vaccine price of US$2. *data for EIR in some cases are not shown in the figure due to a scale problem.

Figure 4

Effect of initial efficacy on cost-effectiveness of all vaccines delivered via EPI with 70-% mass vaccination by transmission setting*. Results obtained assuming a vaccine half-life of 10 years and homogeneity value of 10, and vaccine price of US$2. *data for EIR in some cases are not shown in the figure due to a scale problem.

Figure 5

Cost-effectiveness of vaccines given different levels of mass vaccination coverage by transmission setting*. Results obtained assuming a vaccine half-life of 10 years and homogeneity value of 10, and vaccine price of US$2. *data for EIR in some cases are not shown in the figure due to a scale problem.